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This is to certify that the
thesis entitled

Polarity, Solutions, and Separation Science

presented by

Kenda Jo Lemont

has been accepted towards fulﬁllment
of the requirements for

Masters degree in Biological Science

 

 

% /s/ozm.l

Major professor

Date July 31, 1998

0-7639 MS U is an Afﬁrmative Action/Equal Opportunity Institution

 

 

 

LIBRARY

Michigan State
University

 

 

 

PLACE IN RETURN BOX
to remove this checkout from your record.
TO AVOID FINES return on or before date due.

 

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1198 alumna-bum“

 

POLARITY, SOLUTIONS, AND SEPARATION SCIENCE
By

Kenda J o Lemont

A THESIS

Submitted to
Michigan State University
in partial fulﬁllment of the requirements
for the degree of

MASTER OF SCIENCE
Department of Biological Science

1998

ABSTRACT
POLARITY, SOLUTIONS, AND SEPARATION SCIENCE
By:

Kenda J o Lemont

This document reports teaching separate yet related topics of
chemistry in a uniﬁed, thematic way. The concept of polar molecules with
oppositely charged ends as the driving force behind solutions and separation
science was used to help students link these important and difﬁcult concepts.
To motivate the students and help solidify the concepts, many student-
directed, hands-on, visual, and relevant laboratory experiments were
incorporated in instruction. I observed a positive attitude and even
enthusiasm from the students about learning the concepts and performing the
exercises in the unit. The evaluation instruments indicate that scores are
approximately the same as those achieved in other units. However, the long-
term retainment of the information was considerable, as indicated by
posttests and interviews. This may be attributed to the students’ use of

information in motivating and memorable laboratory experiences.

TABLE OF CONTENTS

LIST OF TABLES
LIST OF FIGURES

INTRODUCTION

Statement of Problems and Rationale for Study
Concept Summary

Review of Pedagogical Literature
Demographics of Classroom

IMPLEMENTATION OF UNIT
I.C. Implementation

H1 and H2 Implementation
Teaching Practices

EVALUATION
Student Surveys
Interviews

Data

Laboratory Assessment

DISCUSSION AND CONCLUSIONS

APPENDIX A: ACTIVITIES, EXPERIMENTS, AND
DEMONSTRATIONS

A1 The Models of Covalent Compounds

A2 T—shirt Chromatography

A3 Chromatography Lab — Extraction of Candy Coatings
A4 The Effect of Temperature on Solubility

A5 Demonstration - Types of Mixtures

APPENDIX B: QUIZ AND UNIT TESTS

Bl Molarity and Solubility Quiz

B2 I.C. Unit Test #1 — Polar Molecules and Chromatography
B3 I.C. Unit Test #2 — Solutions and Colloids

B4 H1 and H2 Unit Test

iii

vi

thr—ir—t

25
32
36

40
4O
48
56
61

64

71
72
75
78
85
87

88
89
9O
94
98

TABLE OF CONTENTS (CONT.)

APPENDIX C: PRETEST, POSTESTS, AND SURVEY 104
C1 Pretest, I.C., H1 and H2; Posttest H1 and H2 105
C2 Posttest 1C. 106
C3 Survey H1 and H2 110

LITERATURE CITED 112

iv

LIST OF TABLES

Table 1: Student Survey Results from H1 and H2

Table 2: Percentage of Knowledge Retained

33

47

Figure 1:
Figure 2:
Figure 3:
Figure 4:

Figure 5:

LIST OF FIGURES

I.C. Order of Implementation

H1 and H2 Order of Implementation
I.C. Assessment Results

H1 Assessment Results

H2 Assessment Results

vi

21

21

46

46

47

INTRODUCTION

1. Statement of Problems and Rationale for Study

Before undertaking my research, I had recently completed teaching a
chapter on solutions to my general chemistry students. While planning the
chapter, I realized that a great deal of the background information had been
taught much earlier in a previous chapter on covalent bonding. I
backtracked with my students, reviewing the concepts of polar and nonpolar
molecules with them and drawing Lewis structures to determine polarity.
After the review, we continued studying solutions and what causes a
substance to dissolve in another substance. I felt that they understood the
concept of polarity better at this point because they could use it to make
predictions. Being able to apply the information helped them to better
comprehend it. In addition, being conﬁdent about their knowledge of
polarity helped them comprehend the forces involved in solutions.

Remembering this when contemplating a unit to modify for my thesis
project, I decided to develop a comprehensive, thematic unit involving the
concept of polarity and its relation to solutions and separation science.
Teaching the unit in this thematic way should help students better

understand all three concepts. Polarity without an application is difﬁcult to

grasp and solutions and separation science without understanding the
concept of polarity is impossible to grasp. In addition to developing the unit
with an overlying theme of polarity, I also decided to focus on using more
hands-on material than in a typical unit. Incorporating separation science
and chromatography would add an important “fun factor” into the unit. In
the past, students had enjoyed working with chromatography because of the
dramatic color changes and the directness and ease of the laboratory
experiments. Finally, my unit also emphasized application of the content to
enable students to envision and appreciate the purpose of the material they
learned.

With the textbook I was using at the time, Chemistry, 1983 (Merrill
Publishing Co.), I realized that it was necessary to reorganize the order that
topics were presented. I had to decide when the unit should be taught
because covalent bonds and polarity were presented much earlier than
solutions. The only information in the chapters between polarity and
solutions necessary for students to learn before the teaching of my modiﬁed
unit was general information on gases. In dealing with the solubility‘of
different states of matter, some background information on the kinetic theory
was needed. The order of teaching was then decided as kinetic theory, then

the combined unit covering polarity, separation science, and solutions.

After teaching the unit for one year I began teaching in a different
district with a different book, Chemistry, VisualizingMatter, 1996 (Holt
Publishing). Again, I had to decide where to place the unit. I was teaching
one section of advanced chemistry and two sections of general chemistry.
The advanced class had not covered the information contained in the unit
very thoroughly the year before, so I decided to teach the unit to both
classes, at different times. Both classes were using the same book, but were,
of course, at different places within it. For the advanced group, I taught the
unit toward the beginning of the year, when they reached the chapter on
solutions and colloids. In keeping with the thematic concept of the unit,
some information from an earlier chapter on covalent bonding and polarity
was reviewed. For the general chemistry group, I taught the unit in the third
marking period when they reached the earlier chapter covering covalent
bonding and polarity. Teaching the unit to three different classes using two
different books at two different levels made me realize that the unit was very
adaptable. The unit can ﬁt into a general chemistry curriculum at the point
that students are ready to learn about molarity. For an advanced class, it can

be taught during a unit on solutions and solubility.

This thesis focuses, again on three main concepts:

1. Laboratory based, hands-on learning

2. Contextual, real-life application of concepts

3. Unifying concept of polarity
II. Concept SummaryI

The information for the concepts covered in this unit was compiled
from various high school chemistry textbooks as well as “Inorganic
Chemistry; Principles of structure and reactivity” by James E. Huheey and
“Chemistry” by Bailar, et. al. The ﬁrst concept was that of polarity, or
unbalanced charge of a molecule. Basically, this unbalanced charge is a
result of two or more atoms sharing electrons unequally. One atom, with a
higher electronegativity, will have a stronger attraction for the shared
electrons and will result in that side of the molecule having a slightly
negative charge. The other atom, with a low electronegativity, will have a
weaker attraction for the shared electrons and a slightly positive charge.
This charge difference varies depending on the atoms involved. Therefore
different molecules have differing degrees of polarity, resulting in different
characteristics such as reactivity, solubility, and boiling point. The polarity
of molecules can be predicted by using a combination of molecular
geometry and electronegativity differences. Learning these concepts related

to polarity was one main objective of the unit.

 

Once the idea of polarity was understood, separation science, an
application of this concept was introduced. Polarity, in addition to molecule
size, is what allows components of a solution to be separated from one
another in chromatography. The substance to be separated is concentrated in
an area of the stationary phase and a solvent is passed over it. The
components of the substance will move along the stationary phase at
different rates, according to their attraction for the solvent, attraction for the
stationary phase, and size of the molecules involved. This attraction is based
on the “like dissolves like” concept of solutions. Molecules with similar
degrees of polarity will be attracted to each other and therefore separation of
the molecules within a sample can occur.

A natural transition to studying solutions followed the section on
chromatography. Using the idea of “like dissolves like” and the knowledge
gained about polarity of different substances, students predicted whether two
substances would be soluble in each other. Factors affecting solubility and
units of concentration were also taught in this section, with an emphasis on
mathematical manipulation. From this, the idea of suspensions and
emulsiﬁers were introduced. A demonstration on making oil and water mix
by adding detergent allowed the student to realize that “like only dissolves

like” can be overcome by simply introducing a kind of mediator that bridges

.._-.. — -__.__._-.._..__ . . -_. * h... ..._ .g

the two dissimilar substances. Macromolecules with polar and nonpolar
parts serve as this emulsiﬁer. The polar end is attracted to the polar
substance and the nonpolar end binds to the nonpolar substance. If the
emulsiﬁer is then dispersed evenly throughout the mixture, the suspension is
then stabilized and the two substances remain uniformly mixed throughout.
Some examples of emulsiﬁers were discussed, in addition to a comparison

of soap and detergent.

111. Review of Pedaggggzal Literature

AS professionals, teachers are continuously trying to improve their
teaching in order to promote better student learning. We discuss with our
peers methods of curriculum delivery, classroom management, and
assessment, with the motive of becoming a better teacher. “What helps our
students to learn more? What can we do to increase their understanding?”
These questions lead us to assess both what we teach in our classes and how
we teach it. Three areas in which I focused my research were: 1) the
effectiveness of hands-on activities to student learning; 2) the importance of
contextual teaching, or making science relative; and 3) the positive

consequences in linking concepts in a unifying way.

I. The Eﬂectiveness of Hands-0n Activities in Student Learning

Teachers of all disciplines and levels go through the self-assessment
introduced above, but in science speciﬁcally we are led to the question of
using hands-on activities to promote learning. “How much do hands-on
activities help my students learn? Does it depend on how I implement them
in my curriculum? Do all students learn better by engaging in hands-on
activities?” It seems that the researchers are still contemplating the beneﬁts
of laboratory activities to student learning. It will be shown that some
research supports the effectiveness of hands-on activities for better student
learning, some research indicates that this is not the case, and many experts
agree that effectiveness is dependent on the implementation and evaluation
of the laboratory experience.

Students can learn by watching and listening but some results suggest
that higher achievement is associated with getting involved in a more overt
manner (Tobin, 1990). Getting involved in laboratory activities can help
promote intellectual development, inquiry, and problems solving skills. It
can also assist in developing observational and manipulative skills and in
understanding science concepts (Hofstein and Lunetta, 1982). These
researchers indicate that using hands-on activities engages the students in a

way that is not possible outside of the laboratory. This engagement allows

for deeper understanding of the concepts and of the process of science. It
seems that teachers of science agree. In a survey performed by Weiss
(1987), over 75% of secondary science teachers felt incorporating laboratory
activities heavily into the curriculum increased the effectiveness of the
course. In addition to the opinions of teachers, other sources support the
effectiveness of a laboratory-based class. In a study by Stohr-Hunt (1996),
“students who engaged in hands-on activities every day or once a week
scored signiﬁcantly higher on a standardized test of science achievement
than students who engaged in hands-on activities once a month, less than
once a month, or never.” The standardized test in this case was not focused
speciﬁcally on science process outcomes yet the impact of increased
frequency of hands-on experience was still signiﬁcant. It seems that the
students involved in the study became more knowledgeable by becoming
more active in learning science. It is possible that the activities involved
help motivate students and increase their interest in science, thereby
improving their performance. In a study by Renner et. a1. (1985), students in
a physics class were separated into two groups. One of the groups collected
and analyzed data in a laboratory experiment. The other group was given a
set of data to analyze. The students who experienced the data collecting had

higher achievement and liked physics better than the students who were

given the second-hand data to analyze. Other researchers support the idea
that laboratory experience promotes positive attitudes and improves
motivation (Hofstein and Lunetta, 1982; Brownstein and Destino, 1995;
Tobin, 1990). By participating and taking a more active role in the learning
process, students’ interest improves. They begin to question their own
misconceptions and try to formulate a resolution between what they knew
and what they are observing. This process of equilibration then leads to
better acquisition of new concepts (Glasson, 1989).

Although implementing hands-on activities in the classroom is
admired, some researchers indicate that students’ results do not support it as
an effective learning method. On the contrary, there is much evidence to
suggest that laboratory activities fall short on achieving the potential for
enhancing student learning and understanding (Tobin, 1990). “A
predominance of research indicates that science laboratory activities have
neither helped nor hindered students’ acquisition of science” (Lehman,
1990). In this study, students’ verbal interactions during laboratory
activities were monitored. He found that a great percentage of student
laboratory time is spent trying to ﬁgure out the procedures. This leaves little
time for data taking, analysis, and interpretation of the signiﬁcance of events

occurring during the experiment. Glasson’s (1989) study indicated that

physical manipulation of the laboratory equipment was not a factor in
improving declarative knowledge achievement. Students in his study were
separated into two groups. One of the groups was presented data by teacher
demonstrations. The other group used hands-on activities to acquire the
same information. Both groups were given the same lectures, readings and
class assignments. The student achievement on conceptual knowledge was
not signiﬁcantly different. The only area in which the groups varied
considerably was in tests on procedural knowledge.

Although it seems that researchers are split on the overall
effectiveness of laboratory activities, they do agree that in order for activities
to be at all effective there must be substantial teacher preparation. The ﬁrst
step necessary in preparation is to match the objectives desired with an
appropriate exercise to meet the goals. Oﬁen times the use of laboratory
work fails to meet its objective because this crucial step is missing. Some
science educators argue that the laboratory is only suited for certain types of
knowledge acquisition and exercises other than these do not prove
beneﬁcial. “One reason for the failure of many science courses is the
attempt to use the practical laboratory work for aims to which it is ill-suited,
such as teaching theoretical concepts, instead of focusing on the real aims,

namely the development of basic process skills, a ‘feel’ for natural

10

phenomenon and problem solving skills” (Tamir, 1989). Tobin (1990)
focuses on the importance of constructivism in the classroom and laboratory.
He indicates that students must be free to pursue solutions to problems that
interest them and construct knowledge based on these pursuits. He declares
the teacher’s role is to allocate tasks and the learners will determine whether
or not the tasks become problems. Other researchers feel that constructivism
and “doing science” are not the only effective kinds of laboratory exercises.
Wilson and Stensvold (1991a) identiﬁed several student outcomes ﬁom
laboratory experiences:
a) developing capabilities to perform laboratory techniques and
methods in order to obtain reliable and accurate information;
b) gaining experience and learning about the universe ﬁrst hand,
using current scientiﬁc viewpoints, materials and processes;
c) comprehending, illustration, explaining, and applying science
concepts, theories and theoretical structures;

d) learning to apply facts and principles to new and novel situations
and to real world concerns using appropriate analytical, creative,

and critical thinking skills; and
e) accepting new ideas while demanding testability with appropriate
analysis as a basis for making reasoned judgements and decisions.
These goals, they believe, can be met using a variety of types of laboratory
exercises. In their article they quote an argument of some researchers that
“veriﬁcation laboratories are merely recipes fostering little creative thinking

and do not adequately represent true scientiﬁc effort. Students should learn

to solve problems through their experience in the laboratory and the only

11

way to do this is through true problem solving.” Their response to this
argument is that there are many ways of learning, many things to learn and
many learning styles. They indicate that based on this, teachers must plan
exercises, taking into consideration who they are planning the exercise for
and what they want the learner to obtain from the exercise. They state that
to be effective, “laboratory-centered instruction must reﬂect the nature of
science, the nature of knowledge, and the nature of students.”

Once a teacher has chosen an exercise that meets the intended
objectives, the next step is to prepare the students adequately for the tasks in
the laboratory. Tamir, (1989) proclaims that pre-lab discussion is essential
for clarifying laboratory exercises and relating them to theoretical concepts.
A pre-lab discussion helps students to become familiar with the procedures
necessary to perform the experiment. This allows them to focus on data
taking and analysis throughout the activity. Lehman, (1990) found in his
study that “the procedural complexity of many laboratories would require
students to refer frequently to written laboratory procedures which would
function as an external memory aid. Gaps at any point in this complex
process would tend to reduce the effectiveness of the activity.”
Demonstrating these more complicating procedures and answering

procedural questions helps to prevent the gaps Lehman was referring to.

12

Tamir (1989) reported that inquiry oriented activities can be very demanding
of students, asking them to incorporate knowledge of subject matter,
manipulation of variables, and proﬁciency in using laboratory equipment.
Having students gain a basic command of each component before
integrating them increases the chance of student success. In addition to
clarifying procedures, a pre-lab discussion helps to clarify the purpose of the
experiment and ties in the concepts from the lecture and reading material.
“Student preconceptions should be measured to structure pre-lab instruction
to insure that key concepts are familiar to students prior to their participation
in laboratory activities” (Wilson and Stensvold, 1993). If the focus of the
laboratory exercise is one of constructing knowledge, this clariﬁcation of
concepts can be veriﬁed in post-discussion, rather than in pre-lab.
Post-laboratory discussion is another important aspect in making
hands-on activities effective. Helping the students to evaluate the validity
and importance of their observations and draw conclusions based on their
data enables the student to realize the purpose of the activity. Any questions
or contradictions they developed during the course of the experiment can be
addressed and resolved. Students can discuss their ﬁndings and explanations
and suggest possible extensions to the experiment (Wilson and Stensvold,

1993). Tamir (1989) states that in addition to pre-lab discussion, post-lab

l3

discussion assists students in “making sense of the laboratory experiences
and relating them to the relevant theoretical concepts.” Tobin (1987) agrees
that appropriate pre and post-lab discussions can enhance learning.

In addition to pre- and post-laboratory discussion, the teacher’s level
of participation during the investigation helps to ensure the success of the
activity. According to Wilson and Stensvold (1993 ), depending on the type
of activity, the teacher may monitor and direct student progress in several
ways. In generalization activities, they can check students’ perceptions,
what they attend to, and what they think is not important in building a
generalized explanation of events. In resolution activities, where students
are confronted with unexpected events, ﬁndings, or questions, and try to
come to resolution with them by performing student-designed experiments,
the teacher’s role is slightly different. The role of the teacher in this type of
activity is one of technical assistance. They must be open to the pursuit of a
problem and encourage students to give reasons supporting their decisions
and answers. Teachers must also raise the issues of validity, reliability,
accuracy, and precision during resolution activities. In conﬁrmation
activities, the goals are to reinforce concepts that students are already
familiar with, to apply existing scientiﬁc theories, to practice laboratory

techniques, and to follow directions. If students have been appropriately

14

prepared for the procedural section of the laboratory, the teacher’s role
during the activity is less signiﬁcant. Students can be monitored and
encouraged to make connections and reﬂect on the importance of their
ﬁndings during the accumulation of data. Then, during post-lab discussion,
teachers can assess change in student perceptions and reinforce the
associations students made during the exercise. In any case, the teacher
needs to ensure the success of the laboratory exercise by being an
appropriately active member of the activity.

The ﬁnal step in planning successful laboratory exercises is
evaluation. The students must be evaluated to determine the knowledge
acquired and the laboratory exercise itself must be evaluated to determine its
overall effectiveness. Tamir (1989) recommends that teachers incorporating
laboratory work into their curriculum need to assess with innovative
practical laboratory tests. Assessment using paper and pencil does not fully
evaluate the knowledge gained by hands-on activities. Speciﬁc content
knowledge gained by hands—on activities can be assessed in the traditional
manner, but student performance assessment requires a different approach.
A more authentic assessment is deﬁnitely in order (Stohr-Hunt, 1996).
According to Tobin (1990) evaluation of student learning needs to focus on

what students learn from laboratory activities and how students can

15

represent their knowledge. Using paper and pencil methods, personal oral
interviews and performance tests attempt to encompass the knowledge
acquired, but Tobin (1990) cites cases where these measurements fall short.
He aims for continued research in the use of alternative assessment tasks to
determine what students have learned from laboratory activities. Involving
teachers in the research, not as subjects, but as researchers would be an
effective way to collect data on this topic. In this manner, science teachers
would be doing science while teaching science. The coordination, teaching,
and evaluation of the unit referred to in this thesis is an example of this type
of science teaching and doing. Even without the structure of programs
suggested by Tobin (1990), the evaluation of the effectiveness of hands-on
activities can and should be performed by individual teachers. At the
conclusion of an activity, the objectives that the activity was intended to
address need to be analyzed. Were these goals met? If not, what aspects of
them were missing? How could the exercise be changed to meet the
intended objectives? Wilson and Stensvold (1993) suggest that “evaluation
of labs should not be an issue of ‘good or bad,’ nor a question of inquiry
versus cookbook, but rather an assessment in terms of the class of intended
outcomes.” In assessing the effectiveness of an exercise, keep in mind that

the success is not only determined by student achievement in learning the

16

concepts covered by the laboratory. In addition, we can evaluate the
exercise by the analytical skills obtained and the students’ attitude toward
the project and possibly toward science, in general (Stohr-Hunt, 1996). If
doing a particular exercise has improved a student’s ability to analyze data
and draw conclusions, not only has the content of his or her conclusions
been learned in a way that will help him or her to remember it, but the
process used can be applied to other learning situations. Also, if the student
achieved success or at least enjoyed doing the activity, they will be more
likely to have an open mind and more conﬁdence when encountering a

similar situation. The attitude toward science then improves.

2. The Importance of Contextual Teaching in Science

In addition to focusing on the impact that hands-on activities have on
student learning, we must also focus on other aspects of effective science
teaching. One such aspect is the importance of making science relevant to
students. In a study by Yager and Lutz (1994), it was found that “nearly all
students perceive school science as unrelated to their daily lives. They see
few ties between the science they study and personal concerns such as their
diets, health, hobbies, work experiences, and consumer decisions.” The

result of this is that students do not apply the information they “learn” in

17

science class to their daily lives. The prior knowledge, including
misconceptions, they possessed before they entered the science class has
been altered very little by the time they leave. Even what we perceive as
“successful” science students do not appear to be applying science. In a
study cited by Yager and Lutz (1994), students of college physics and
engineering were tested in order to determine how human learning takes
place. They were chosen because they were academically successful and
researchers assumed they would serve as an example of how successful
learning occurred. The students were given difﬁcult, real-world problems to
solve and the thinking and analyzing process they used to solve the problems
was studied to determine the steps involved. The results indicated, however,
that 85% of the physics majors and 90% of the engineering majors could not
solve everyday problems. The researchers investigated the cause of these
results and found that the students had not changed their personally
constructed explanations when presented with conﬂicting explanations in the
classroom. Yager and Lutz support the idea that contextual teaching will
help alleviate this problem. “Context can make problems considered in
school science synonymous with real world problems. When school science
classes focus on real world problems, there is a good chance that cognitive

scientists will ﬁnd that successful students in school science and technology

18

are also successful in solving problems in the real world, outside of school.”
As science teachers, if we do not make the information we teach relative to
student lives, and challenge their misconceptions, it is unlikely that this

information will remain with our students.

3. The Positive Consequences of Linking Concepts in a Unifying Way

In combination with applying science to students’ lives, we must also
apply the concepts taught in science to each other and focus on teaching for
understanding. Linking concepts to each other helps the students to learn
and apply the information more successfully. A study about two effective
science teachers done by Garnett and Tobin (1989) found that both teachers
were successful in teaching for understanding. They used different styles to
do this. One teacher promoted student independence and self-reliance in the
classroom, where learning was primarily the responsibility of the student,
with the teacher as facilitator. The other teacher played a more active role
by explaining concepts and identifying the logical framework of the
discipline. Both teachers effectively monitored for student understanding by
using questioning and clarifying techniques, either in whole-group or
individual settings. Students were called upon to explain or justify their

answers. Both teachers focussed on tying new concepts to those which had

19

been previously learned. Linking new material to prior information
enhances the probability of meaningful learning.

Teaching for understanding by making new information relative to
students’ lives and to other areas of science, as well as allowing learning to
occur by engaging students in laboratory activities is the focus of my unit.
In reorganizing the order of delivery of information, I was attempting to link
new information to that which had been previously learned, thereby
increasing the probability of meaningful learning. Organizing concepts to
allow better connection between them assists students in developing deeper,
more long lasting learning. The overlying theme of polarity that I have
employed in teaching this unit allows students to make connections and
better understand the concepts of polarity, separation science, and solutions
individually, and in connection with each other. In addition to making these
connections between concepts, I incorporated contextual learning throughout
the unit. By applying the information being taught and learned to real world
situations, I was expecting to increase student retention of information and
application of it to their lives. Some examples of this include:

1. A laboratory involving chromatography has a real-life purpose of
ﬁnding a cancer-preventing yellow dye.

2. The students study vitamins and their comparative solubility in
body.

20

These examples indicate the direction toward applied science that the
unit has taken. Applying new concepts to circumstances that students can
relate to helps them to assimilate this information and retain it. Another way
to help students to apply and remember information is to have them engage
in memorable laboratory experiments and activities. These activities serve
many functions, as described in the previous sections. One important
function that I was striving for was student motivation and engagement.
Creating an activity in which the students can be an active participant
increases the chances that they will become engaged in learning the
concepts. If they are engaged, they are more likely to formulate questions,
identify conﬂicts in their prior knowledge, and ﬁnd ways to resolve these
conﬂicts. It is this resolution that helps to create long-term retention of the
information. In addition to motivating students to become active learners,
executing labs helps to create a visual memory. The chances seem slim of a
student exclaiming, “Oh, I remember that day last year when we took those
notes and learned how to do those problems!” Yet, I had students one year
after being taught the unit who said “Oh, I remember that lab where we
made those T-shirts with different colored ink on them!” Then they
proceeded to recall the information they learned about polarity from doing

the activity. Students learn in various ways. Some learn by asking questions

21

and listening to answers. Some learn by doing things themselves. Some
learn by watching others. Most learn by using a combination of styles. This
combination demands that we as teachers use many teaching styles. If we
were teaching one student at a time, we could assess the learning style that
best ﬁts that individual and teach using that style all the time. This, of
course, is not the kind of situation we have in the classroom. By varying the
styles we use throughout the presentation of a particular unit, we are
increasing our chances of ﬁnding something that works for everyone at some

point.

IV. Demographics of Classrooms

The three classes that were my study group are similar in many ways.
Even the two communities in which the districts are located are similar. The
ﬁrst district is a class B school, from here on referred to as I.C., with
approximately 550-600 students enrolled in the 9-12 high school. The
location is classiﬁed as rural, with many farms, dirt roads, and students
bused in. The socioeconomic status of the community is generally middle
class. A considerable percent of the population commute to larger

surrounding cities or suburbs for work.

22

The second district is a class A school, from here on referred to as H.,
with approximately 1100 students enrolled in the 9-12 high school. The city
itself is not that large but the school district covers a large surrounding area
of smaller towns and townships. Again, a considerable number of the
students are bused in. There is a large variation in the socioeconomic status
of the community. They range from lower middle class to upper middle
class. There is a considerable representation of single parent families in the
community. Commuting into surrounding cities or suburbs for work is
common.

The classes within these two districts are similar also. The ﬁrst group
I taught the unit to, in I.C., consists of three general chemistry classes with
ﬁfty-seven students total. F ifty-three of these students were juniors with two
seniors and two sophomores included. Thirty-three of the ﬁfty-seven
students are female. The minority populations are not represented very well
within these chemistry classrooms. Less than 6% of the LC. study group are
minorities (Hispanic, Japanese, or other non-Caucasian). The average g.p.a.
for the classes of students was 3.32. When I surveyed some of these
students in two physics classes the following year, all except one were
planning on attending a four-year college or university full time after

graduating. The exception was planning on attending a junior college. Not

23

all the students from the unit were in the physics classes for the survey, but
chemistry is generally taken by college prep students. I am assuming that
the actual percentage of students planning on attending a four-year college
or university would not vary much from the physics class survey.

The second group of students the unit was taught to are from the
second district, and will be collectively referred to as group HZ. These ten
students were enrolled in advanced chemistry and were all seniors. Their
average g.p.a. for the group, consisting of ﬁve females and ﬁve males was
3.46 and all were planning on attending a four-year college or university full
time. All ten were in their second year of chemistry with nine of the ten
having taken it the previous year. Of the ten, one is Hispanic and one is
Black.

The ﬁnal group of students consisted of two general chemistry
sections with forty-three students total, from here on referred to as H1. Five
of the forty-three were seniors and the remaining thirty-eight were juniors.
Their average g.p.a. was 3.37 and all forty-three were planning on attending
a four-year college or university full time upon graduation. The class
consisted of twenty-ﬁve females and eighteen males. Again, the minority
population was not well represented with less than ten percent of students

being Black, Hispanic, or other non-Caucasian.

24

IlVIPLEMENATATION OF UNIT

The unit was taught three times, ﬁrst at LG, with three general
chemistry classes, then the following year at H, initially with the advanced
chemistry class, and later with two general chemistry classes. The order of

implementation for the three groups can be seen in Figures 1 and 2.

1. LC. Implementation

A. Polar Molecules

At I.C., the unit was begun with a review assignment of the
differences between covalent and ionic bonds and determining which are
present in certain molecules. After this overview, Lewis structures were then
reviewed. To this review was added the new concept of assigning partial
charges to determine whether an entire molecule was polar.

The “Models of Covalent Compounds” (Appendix Al) activity was
assigned. The students had to construct the models of several molecules,
using ball and stick model kits. They also had to write each molecule’s
Lewis structure, calculate electronegativity differences, assign partial

charges, determine the geometry of the molecule, and then determine its

25

 

Concept

Activity

 

Polar Molecules

Predicting Polarity Practice Assignment (textbook)

 

Models of Covalent Compounds Lab

 

 

Chromatography

Ink Pen Chromatography Activity

 

Extraction of Candy Coatings Lab

 

T-shirt Chromatography Lab

 

 

Test — Polarity and Chromatography

 

 

Solutions

Molarity Calculations (textbook)

 

Quiz — MolaritLCalculations

 

Effect of Temperature on Solubility Lab

 

 

Colloids and Emulsiﬁers

Soap, Oil, and Water Demonstration

 

 

 

 

Test — Solutions, Colloids, and Emulsiﬁers

 

Figure 1: LC. Order of Implementation

 

Concept

Activity

 

Solutions

Demonstration - Types of Mixtures

 

Molarity Calculations (textbook)

 

Quiz — Molarity Calculations

 

Spectrophotometry Lab (textbook, H2 only)

 

Effect of Temperature on Solubility Lab (Hlonly)

 

 

Polarity

Predicting Polarity Practice Assignment (textbook)

 

Models of Covalent Compounds Activity

 

 

Chromatography

T-shirt Chromatography Lab

 

Extraction of Candy Coatings Lab

 

 

Colloids and Emulsiﬁers

Soap, Oil, and Water Demonstration

 

 

 

 

Unit Test

 

Figure 2: H1 and H2 Order of Implementation

26

 

 

polarity, taking in consideration the information they had just acquired about
the molecule. They did this for 13 compounds, and then answered post-lab
questions regarding models of covalent compounds. The purpose of this
assignment was to allow the students to model the three dimensional nature
of molecules. Determining the polarity of a molecule, whether it has two
distinct, oppositely charged ends, is much easier when physically holding a
representation of the molecule. Associating this model with a Lewis
structure helps the students to visualize molecular shapes when the kits are
not available for student use. Visualizing the three dimensional shapes of
molecules can be very difﬁcult and having a hands-on exercise certainly

makes this concept more concrete.

B. Chromatography

The discussion then led to applying the concepts discussed above to
chromatography. A short lab from the Merrill textbook, “Ink Pen
Chromatography,” was performed. Students separated the component dyes
of different ink pens using a variety of solvents and conclusions were drawn
about the relative polarities of the inks based on which solvents could

separate them. A post-lab discussion helped to ensure that students grasped

27

the concept of chromatography so that they could apply these concepts in
more complicated labs in the near future.

At this point, another laboratory exercise, “Chromatography Lab --
Extraction of Candy Coatings,” (Appendix A3) was introduced. In this
exercise, students extract the color ﬁ'om various hard-shelled candies and
attempt to ﬁnd which one(s) have a speciﬁc yellow dye in them. The
ﬁctional premise in the introduction of this laboratory is that the yellow dye
is a cancer-preventing agent. The students’ objective is to ﬁnd other candy
coatings that might contain the same yellow dye. This is a two-day lab in
which students can achieve great success at “real chemistry.” Students were
assigned three different colors or kinds of candies to extract. When the
laboratory work was complete, groups shared data to complete the
comparison of all the colors of all the candies and a post-lab discussion
followed. The students expressed their approval of this colorful, hands-on
experience. Having a laboratory exercise with a real-life theme allows the
students to comprehend the usefulness of the information they are obtaining.
Even in this overly simpliﬁed “ﬁnd the cancer preventing dye” scenario, the
application of chromatography was readily comprehended by the students.

Following this exercise was another colorful chromatography lab

called “T—shirt Chromatography” (Appendix A2). Here, the students

28

brought in cotton T-shirts from home and made various designs on them
with permanent markers. Different solvents were dripped slowly onto the
shirts to separate the component colors of the inks. This exercise allowed
students the freedom to explore and learn on their own. They could make
hypotheses on which solvents would cause which inks to separate and then
draw conclusions on why their hypotheses were or were not supported. The
discovery method of learning can encourage students to be scientiﬁc
thinkers.

At the conclusion of this exercise the students completed a review
sheet, covering the previous concepts discussed. A class review and then a
test (Appendix 32) covering polarity and chromatography was given.
Students were required to explain the concept of polarity and predict the
polarity of compounds, given their electronegativity values. In addition,
questions were asked about chromatography and what type of solvents will
work for what type of substances. Students were required to draw Lewis

structures and assign polarity to molecules.

C. Solutions
Application of these concepts to solutions was the next transition for

this class. The discussion began with a review of the vocabulary of

29

solutions, (solute, solvent, miscible, etc.) and then led to what causes
solutions to occur. Having been introduced to the concept of “like dissolves
like” in dealing with chromatography, they quickly came to the conclusion
that a polar substance could dissolve other polar substances and nonpolar
could dissolve nonpolar. They were given formulas of different compounds
and were asked to predict their relative solubilities based on their
comparative polarities. Making these predictions allowed them to apply
new and old information to solve a problem. Even when their predictions
were not supported, learning was achieved.

This was followed by the quantiﬁcation of solubility using molarity,
molality, and mole fraction. Sample problems were done together in class,
with the difﬁculty of the problems gradually increasing and the dependence
of the students on teacher direction decreasing. Then a small problem set
from the textbook was completed. Students worked together in small groups
to solve the problems, requesting help when they needed it. After several
problem sets were assigned and reviewed, a quiz (Appendix B1) was given.

Once the quantiﬁcation of solubility was mastered, the question of the
effect of temperature on solubility was introduced. “Does increasing the
temperature make more solute dissolve or less? Does it depend on the solute

and the solvent?” After they made predictions the students performed an

30

experiment titled “The Effect of Temperature on Solubility” (Appendix A5).
Various amounts of ammonium chloride were dissolved in test tubes
containing a constant volume of water. The temperatures at which the
substance began to precipitate out of solution were measured. After
collecting this data, the students plotted it to produce a solubility curve.
They then made predictions about the solubility of ammonium chloride at
other temperatures and compared their graph to a standard. In this exercise,
students were asked to think ahead of time about what would happen in the
experiment and make predictions on the results. This process allowed
ownership of the knowledge. Having made a prediction, they seemed to be
quite interested in whether or not they were right. In the event that they
were wrong, they tended to question the results and ﬁnd out what was wrong
with their earlier logic. Also, comparing experimental results to standards
helps promote careful laboratory techniques. If their results are far from
what they expected, the students can see it themselves and can repeat the

experiment.

D. Colloids and Emulsiﬁers
Finally, the question arose, “What happens if two things are not

soluble in each other; can we do anything about it?” To introduce and

31

answer this question, a demonstration was performed. First, oil and water
were mixed to demonstrate a suspension. When the suspension settled, soap
was added and the mixture was shaken. The oil and water remained as a
colloidal suspension. “Did the soap change the chemistry or pOlarity of
either of the substances?” The soap simply acted as a bridge, linking the
nonpolar oil to the polar water. Performing the demonstration was a visual
example of emulsiﬁcation. Students can see the process of emulsifying
occurring, which helps them to better understand it, and they can attach a
visual memory to the content, allowing them to remember and relate it to
new information. The students were then given a review assignment from
the textbook, which addressed these frnal concepts of emulsiﬁers and
colloids. The answers were discussed in class and then a test (Appendix B3)

was given.

11. H1 and H2 Implementation

The following year, I changed school districts and taught the unit to
an advanced chemistry class, group H2, during ﬁrst semester, then to my
two general chemistry classes, group H1, during the third marking period.
In addition, a co-worker taught this unit at the same time to her two general

chemistry classes. The order of the unit was changed from the ﬁrst time it

32

was taught and a few other changes were made (see Figures 1 and 2). One
major difference was that learning of the unit was measured with two major
tests the ﬁrst time (at LC.) and only one test for the next two presentations
(at H). The unit took a little less than ﬁve weeks the ﬁrst time it was taught
and a little over ﬁve weeks the next two times. Also, although this unit
coordinates well with most general chemistry texts, using a different text
changes assignments and discussions to a certain degree.

Previous to the teaching of the unit, the advanced chemistry class, H2,
had some knowledge of solutions, polarity, and separation science from their
ﬁrst year of chemistry. In addition to this background, they had covered
concepts of thermodynamics and gases, which the general chemistry class
did not have previous to the teaching of my unit. These concepts helped the
advanced students to apply the concepts of kinetics to solutions but I don’t
believe this is a prerequisite for the polarity, solutions, and separation

science unit.

A. Solutions
The unit, in both the H1 and H2 groups, was initiated by a discussion
with a demonstration, “Types of Mixtures” (Appendix A5). The

demonstration involved using four mixtures to introduce students to solution

33

terminology. The conclusion of this discussion led to an introduction of
concentrations of solutions. The different ways that concentration can be
expressed were discussed and then sample calculations were performed for
molarity (moles/L) concentration units. There were homework problems,
quizzes, and a laboratory to ensure the assimilation of this information. The
HZ group performed a basic spectrophotometry lab exercise from the
textbook. They attempted to ﬁnd the concentration of an unknown sample
of iron (III) chloride by graphing the absorption data of their standards and
comparing the unknown to their graph. The data was inconclusive, at best,
so a different exercise was selected for the H1 group. They performed the
laboratory exercise, “The Eﬂect of Temperature on Solubility ” that was also

executed at I.C.

B. Polarity

Following the teaching of molarity, the idea of what causes a solution
to occur was discussed. Why did some things dissolve in water and some
didn’t? Could we predict what was going to dissolve and what wasn’t, for a
given solvent? At this point, polarity was discussed once again. The
students had prior knowledge about polar bonds, but not polar molecules.

Several examples of these predictions were given, using Lewis structures

34

and assigning partial charges to atoms. Then the “Models of Covalent
Compounds” activity with molecular model kits was assigned. The
discussion then led to using this material to predict solubility of different

compounds.

C. Chromatography

The natural transition ﬁom this point was “What can we do with this
information?” It was time for an application of solubility principles,
chromatography. First, the “T-shirt Chromatography” laboratory exercise
was performed. The third time this exercise was attempted by me it became
an outside, picnic table lab. The fumes are a little overwhelming for four
hours of chemistry labs. After completion of the lab exercise and write up,
we moved on the a lab the students affectionately call “The Candy Lab.”
Like the LC. group, the H1 and H2 groups also enjoyed this of this colorful,

hands-on experience.

D. Colloids and Emulsiﬁers
Finally, the concept of emulsions acting as a bridge between polar and
nonpolar substances was discussed. The demonstration involving oil, water,

and soap was performed, creating a visual representation of a working

35

emulsion. The students were assigned to ﬁnd the names of several products
at home that contained emulsifying agents and identify, from a list, the type
of agent in each of them. This helped the students realize that chemistry is
not just in chemistry class.

Other applications of solutions were discussed, such as vitamin
solubility. Those vitamins that are soluble in water are much less likely to
be ingested to a toxic level by the body because they get ﬂushed out of the
system. However, fat-soluble vitamins like A and E, can reach toxic levels
because the liver does not break them down as easily. The students readily
applied this to their own vitamin taking practices. At this point, the students
were given a review assignment. The answers were discussed in class and a

test (Appendix B4), covering the entire unit, was given the following day.

111. Teaching Practices

I altered my normal practices in a few ways when teaching this unit.
First was using laboratory exercises and hands-on activities as a basis of
instruction. Implementing student-directed learning through laboratory
work is extremely important, but also extremely time-consuming. Through
my research summer at Michigan State University I found the time to test

student labs, modify them and even do a little creating. Being able to take

36

the time to develop and then implement a cohesive unit was in a sense, my
own experiment. Just as students learn more by actually doing the
experiment, (even if they know what the results should indicate) I also
learned by doing. I knew (and still know) that laboratory work is an
essential part of learning science. But knowing it and seeing the effect of it
are two different things. I found that teaching this unit has been a big push
for me to implement more student-directed learning throughout the rest of
the chemistry curriculum. The difﬁcult part is to be able to ﬁnd or create
labs that directly tie in with the concepts covered in lecture/discussion. If
this association does not occur, laboratory exercises can still be fun, but not
relevant.

Another technique incorporated in the unit was focusing on a theme,
polarity, the cause of solutions to occur (or not.) Students were introduced
to the concept of polarity or polar covalent bonds in the chapter preceding
this unit. They could calculate, given an electronegativity chart, whether a
given bond was ionic, polar covalent, or nonpolar covalent. The depth to
this information was missing, however. The “SO WHAT?” was not
answered in the previous chapter. The idea was to build on their previous
(and fresh) knowledge of this concept, to repeat it, apply it, and repeat it

again. In this manner the concept of polarity would be better understood

37

because the students could see what it relates to and how it can be used to
predict something. The concept of a theme is like a circle. Learning about
solutions could not be done without learning about polarity and polarity
could not be thoroughly understood without applying it to a principle such as
solutions or chromatography. The main reason I focused on the use of
themes in this unit is because I believe that is the way we all learn. When
incorporating new information, we ﬁnd the ﬁle in our brains where this new
stuff will ﬁt. The more we learn about it, however, the more ﬁles we need to
put it into. Learning is being able to access those ﬁles and relate them to
each other to better understand “the big picture.”

Using themes is something I have done in the past, in order to provide
a better explanation to students. Focusing on it, however, has made me
realize that it is something I need to continuously strive for because it
enhances the learning process tremendously.

The ﬁnal focus of my unit was to teach contextually. In the past, I
have found that students respond well to contextual teaching so I try to
implement it in any unit, but I wanted to make it a particular area to accent
in this unit. Teaching in context and relating the information presented to
student’s lives helps make the learning personal for students. Knowing how

the information that they are learning can be applied brings relevance and

38

purpose to acquiring the knowledge. In this unit, the contextual teaching
was evident in the laboratory exercises. For example, using chromatography
to identify a speciﬁc dye in “Extraction of Candy Coatings” mirrored how
chromatography might be used outside of the chemistry classroom. Also, by
creating a standard graph in “The Effect of Temperature on Solubility”
students gain a better perspective on how these standard graphs are actually
prepared, giving them a more realistic perspective of the information the
graph contains. Discussions throughout the unit, such as the one about
vitamin solubility in the body, also helped to relate the concepts students

were learning to their own lives.

39

EVALUATION

This unit was an effective way to teach polarity, solutions, and
separation science as substantiated by several types of assessment. One was
simply my observation of student involvement, motivation, and attitude.
Also, a student survey (Appendix C3) was given to the H1 and H2 group,
asking about their overall impression of the unit and perception of their own
understanding of the unit. In addition, student scores on pretests, unit tests,
unit work (labs, homework, etc.), and posttests were evaluated. Finally, two
students were interviewed about their opinions and content understanding of
the unit. The compilation of these assessments aided in the overall analysis

of the effectiveness of the unit.

1. Student Surveys

In the student survey given to H1 and H2 students 92 % agreed or
highly agreed that the labs helped their understanding of the material and the
other 8 % were indifferent, at worst (Table 1). Eighty-two percent of
students agreed or highly agreed that the labs motivated them to learn the
material whereas 12 % were indifferent and 4 % disagreed. Student also

seemed to believe that the labs tied in well with the instruction: ninety

40

Table 1: Student Survey Results from H1 and H2

 

 

n=50
1 — highly disagree 2 — disagree 3 — indifferent 4 — agree 5 - highly agree
Percentages rating 1 2 3 4 5

l. I found this unit to be organized. 0 4 10 58 28

2. I found the labs helped my understanding of 0 0 8 4O 52
the material.

3. I found it easy to make connections and draw 2 4 20 58 16
conclusions between polarity and chromatography.

4. I found the labs tied in well with the instruction. 0 O 10 42 48

5. I found the labs motivated me to learn the material 0 4 12 50 32

6. The demonstrations proved beneﬁcial in under- 0 0 8 54 38
standing concepts.

7. My understanding of the material in this chapter 0 16 38 38 8
is greater than material from previous chapters.

8. I understand the effect polarity has on whether or O 14 8 52 26
not a solution will occur.

9. I understand the difference between a polar covalent O 12 14 48 26
bond and a nonpolar covalent bond.

10. I understand how an emulsiﬁer works. 4 2 8 56 30

11. I understand the difference between a detergent and 2 8 6 46 38
a soap.

12. I understand the practical applications of chroma- 2 4 6 6O 28
tography.

l3. I understand how electrons could be shared unequally 0 12 22 48 18

in a covalent bond.

14. I understand how molecular geometry is used to 2 10 20 42 26
determine molecular polarity.

 

4l

percent agreed or highly agreed with this statement and 10 % were
indifferent. Relating the demonstrations to the course work was important to
the students based on the fact that 92 % of them agreed or highly agreed that
the demonstrations proved beneﬁcial in understanding concepts. The other 8
% were indifferent. The students also rated the organization of the unit
relatively high, with 86 % agreeing or highly agreeing that the unit was
organized, 10% indifferent, and the other four percent disagreeing. The
ratings for the effectiveness of the thematic approach were positive, but not
quite as high as the laboratory/demonstration evaluation. Seventy-four
percent agreed or highly agreed that they found it easy to make connections
and draw conclusions between polarity and chromatography. Twenty
percent were indifferent and 6 % disagreed or highly disagreed. Seventy-
eight percent of students agreed or highly agreed that they understood the
effect polarity has on whether or not a solution would occur. Eight percent
were indifferent and 14 % disagreed. Seventy-four percent agreed or highly
agreed that they understood the difference between a polar covalent bond
and a nonpolar covalent bond. Fourteen percent were indifferent and 12 %
disagreed.

The students were also invited to make written comments about the

organization of the unit and the support of the labs and demonstrations. One

42

student wrote, “The labs worked well. Things being discussed in the chapter
could be understood more when we could visually see how what we learned
applied to the lab.” Another stated, “I thought the organization was
wonderful. I liked how we’d get a small amount of notes and then an
assignment to do on our own. I felt like I learned on my own terms, my own
way so I had a better understanding.” The same student also had positive
comments about the labs and demonstration. “The lessons led up to the lab
and provided enough information for self-direction when we got to the
experiments. It is helpful to see the concepts.” More positive comments
were, “I think that the labs did help. Yes, they did tie in with the instruction.
I was surprised to ﬁnd that they did help with my understanding.” “I don’t
think that it could have been much better.” “Yes, I found it relatively easy to
connect concepts from the chapters, like covalent bonds, electronegativity
differences, etc. The demonstrations and labs are very helpful. They tie in
directly with the material and let us see through our own eyes what is going
on. The responsibility given to us and the neat demonstrations deﬁnitely
motivated me.”

The few negative comments about the organization of the unit were

generally in reference to the confusion of skipping around in the book. The

43

students who had a hard time following the chapter jumping thought that
better-deﬁned notes would help avoid the confusion.

The students were also asked about their perception of their own
understanding of the unit (Table 1). In comparing their understanding in this
unit compared that in others, 84 % agreed, highly agreed, or were indifferent
that it was greater in this unit. This indicates that 84 % felt they learned as
much or more in this unit as in others. The remaining 16 % disagreed, or
thought they understood more in other chapters. When asking about speciﬁc
topics, the highest self-evaluation was regarding chromatography. Eighty-
eight percent of the students surveyed agreed or highly agreed that they
understood the practical applications of chromatography, 6 % were
indifferent and 6 % disagreed. This was most likely due to the number of
experiments involving chromatography. Also rating high were the students’
opinions on their understanding of emulsiﬁers. Eighty-six percent agreed or
highly agreed that they understood how an emulsiﬁers works. The students
might remember this well because of the demonstration involving soap as an
emulsifying agent between oil and water. Also, this subject was covered
toward the end of the unit, so it might be easier to remember. In contrast,
sections on electron sharing and molecular geometry, which were taught in

the early stages of the unit, had the two lowest individual topic ratings.

Sixty-six percent agreed or highly agreed to their understanding of how
electrons could be shared unequally in a covalent bond and 68 % agreed or
highly agreed to their understanding of how molecular geometry is used to
determine molecular polarity.

In the written response portion of the survey, these numbers were
supported by comments. The question asked in the survey was “How did
your understanding in this unit compare to previous units? How did your
scores compare?" Some answers follow.

“I do pretty average in all chemistry chapters. I average a B to A- for
the chapters. This chapter was not difﬁcult at all.”

“My scores were the same and so was my understanding, but my
scores do not accurately affect my understanding because I always manage
to understand the unit and still get low scores.”

“My understanding is really beginning to increase. Especially
compared to last year. My scores could still be better, but that is mainly my
fault.”

“My understanding of this unit might have improved a little. My
scores were about the same. This unit was more fun.”

“I understood very well, and very easily. I was more comfortable

with this unit and also scored better, I believe.”

45

“I think I had a better understanding this time around. My test scores
were all higher than I thought. They would be a very pleasant surprise.”

“I feel I learned more from the labs than the other chapters.”

“I think I understood this chapter more, that in the sense that I will
remember it longer. I usually remember the information until we take a test,
then its gone.”

“This unit was much more exciting and was made much clearer.
There was a lot of information given in this unit, but it seemed more
organized and well planned out. My scores didn’t change much, but the
impact was much greater.”

Although the above comments are generally positive, there were some
students that did not feel that the unit was a success for them. “I think I’m a
bad example, but I didn’t have an easy time with this unit. I didn’t do good
on the test.” “I did bad (sic.). My score was lower than the previous unit.”
“My understanding compared to the previous units was lesser. My scores

’9 ‘6

seemed about the same, though. (My understanding was) not good. My
test grade was the worst yet, a B-.”
The students’ impression of their own knowledge improved compared

to that from previous units. In comparing the scores on this unit to marking

period grades, I found that they were quite similar. For I.C., the unit average

46

was 79 % and a marking period not including the unit averaged 82 %. In the
H1 group, the unit average was 83 % and the marking period average was 84
%. The results were similar for the H2 group with the unit average at 85 %
and a marking period average of 88 %. These scores indicate to me that the
students performed similarly to previous units. Even though all three groups
scored a little lower on this unit than a marking period average, this was not
signiﬁcant enough to lower my perception of the success of the unit. The
marking period averages include current event scrapbooks, which tend to
bring the students’ grades up slightly. General chemistry students do not
easily understand the concepts presented in this chapter, so the fact that the
scores are slightly lower is not necessarily unexpected. A more accurate
representation of unit success would be to compare the scores achieved by
students taught the “old” unit to those taught the “new” unit. However,
since the “new” unit is a compilation of concepts from different chapters,
this data would not be possible to obtain. More important than test scores, in
determining the success of the unit, are retention scores and student

attitudes.

47

11. Interviews

In addition to the surveys, casual comments, and observations, student
attitudes were measured by interviews. I interviewed two above average
female students, one from I.C., one from H1, and a co-worker from H. who
taught the unit to her general chemistry students. I decided not to interview
a student from the advanced group because the comparison might not be fair,
since those students had one more year of chemistry background. In
retrospect, I feel that the information gained from this interview would have
outweighed any bias by the advanced student. The three interviews were
informative and interesting, in different ways.

The ﬁrst interview was with “Allison”, a student from H1. Allison is
an above average student, earning 84 % average on her tests for the year and
88 % average marking period grade. For this unit, she scored 91 % on the
test and 92 % for the unit average. Her opinion of the labs in this unit was
very high. She said, “The labs were cool. They showed how the reactions
worked.” At the end of the interview, I asked her if she had anything else to
add and she volunteered, “I really liked the labs that we did. They were
fun.”

She also felt that the labs and demonstrations added to her

understanding of the unit. When asked about her understanding of this unit

48

compared to others she commented, “some parts (I understood) more cause
of labs, but basically about the same.” When I was questioning her on how
to make two immiscible substances form a solution, she mentioned that soap
could be used. She remembered that soap was an emulsiﬁer “. . .because you
put it in with the corn oil and the water and when you added soap to that it
stayed mixed and before it wouldn’t.”

In addition to asking her opinion of the unit, I asked questions to
determine how well she understood the content. I began by asking her what
polarity was and she replied, “when an element (sic.) has a positive and
negative end.” I asked her how she would determine the polarity of a
substance and she stated, correctly, that she would make a Lewis structure.
She was however a little confused on the speciﬁcs of assigning partial
charges to the elements involved in the bond. We moved on to how polarity
affects solutions. She said that if the polarities were not the same, “solutions
won’t occur. Like dissolves like; polar dissolves polar and in some
circumstances, nonpolar dissolves nonpolar.” I probed by asking her how a
polar solution occurs and she replied, “The positive end of one (substance) is
attracted to the negative end of the other and pull each other apart.” We
moved on to how concentration is measured and she remembered it was in

units of molarity, or moles per liter. She then proceeded to solve a molarity

49

problem for me, explaining her steps as she did so. The problem involved
solving for molarity of 33.5 grams of sodium chloride dissolved to make 350
milliliters of solution. Following is her thorough and correct explanation.

“First you start with what you’re given. You put 33.5 grams of
sodium chloride per 350 milliliters. Then you have to get it to moles over
liters so you write that at the end and it all equals that. So you have to
convert grams to moles so you put grams on the bottom of the chart and
one mole goes over that. And you have to ﬁnd out how many grams are in
that (sodium chloride) so you look on the periodic table and add it up and
then sodium chloride is 58.44 grams. Once you have that converted, you
have to convert milliliters to liter... One thousand milliliters goes on top of
one liter cause one liter has to be on the bottom and they all have to cancel
out. Then you multiply everything through on the top and divide by
everything on the bottom.”

She also showed good recollection of the laboratory exercises, their
purpose, and the concepts involved. I asked her about the purpose of the T-
shirt lab and she replied, “to Show how chromatography works and how the
polarity of the substance you put on the shirt and how it is affected by
different polarities of the substance you put on the shirt, like liquids, and

how it pulled apart different colors.” She remembered that the inks were

50

nonpolar and therefore the solvents that moved them were nonpolar. I asked
her if water would separate the colors in the inks and she said, “no, because
water is polar and the inks were nonpolar.” She summarized the main points
of the candy chromatography lab recalled that the separation in the
chromatography was caused by, “the polarities of different substances.”

In discussing emulsions, she remembered that they worked to join a
polar and a nonpolar substance, but was a little confused in her explanation
of how this worked. “Because they’re all mixed up and they’re not actually
staying. It forms around of them and it like gels around it sort of and it
makes the whole thing be a positive or a negative, whatever it needs to be to
stay with the other one.” The lack of accuracy of this explanation is
probably due to the fact that it was not covered as thoroughly as some of the
other concepts in the unit. In addition, although a demonstration was
performed, the students did not do any experiments with this topic.

The other student interview was performed at 1C. approximately 10
months after the unit was taught. I returned just after spring break to re-test
students from the two physics classes that had taken chemistry the previous
year. During this time, I also interviewed “Kari”, a chemistry student ﬁ'om
the previous year. Kari was an above average student with a wide range in

test scores which reﬂected her interest in the content being taught. Her test

51

grades average 87% for the year, varying from 74% to 98%, and her
marking period grades averaged 83 %, varying between 72% and 94%.
During this unit she earned an 85% unit test average and 89% for the unit
average. Kari’s recollection of the unit was that “it was difﬁcult to
understand.” Throughout the interview it was apparent to me that some
concepts were difﬁcult for her to understand and remember. However, she
did recollect a considerable amount about chromatography and polarity from
the experiments. I asked her if she thought that doing the labs helped her to
learn and remember the concepts. She said, “If I didn’t remember having
such a fun time doing the T-shirts, I really wouldn’t have remembered about
the polarity of it. If we had just done the unit it would’ve been so easy to
misplace that little memory.” She also said that the labs were “the best labs
we did because there was more involved and a lot of color.”

In questioning Kari about the content of the unit, she deﬁnitely
showed less retention than Allison. This is understandable given the amount
of time that had passed since the teaching of the unit. Initially, she seemed
to remember very little, but as the interview progressed and her memory was
triggered by the conversation, her responses for some content areas
improved. I started by asking her what she remembered about the unit. She

stated, “that it was difﬁcult to understand.” I asked her what she

52

remembered about the labs and she recalled quickly the T-shirt laboratory.
“We drew on the T-Shirts with ink pens and put stuff on them to make them
run, like nail polish remover and things like that. I asked her what caused
the colors to run and she replied, “the polar and nonpolar characteristics.”
She also recalled the candy chromatography lab and summarized the general
procedure and purpose. When I asked her how chromatography works, she
initially replied, “I don’t know.” I redirected with asking her about polarity
and she responded, “If the substance has positive and negative ends, it
attracts itself to another substance and it will allow it to be separated, like
pulled apart. If you put black on a T-shirt and you put the nail polish
remover on it the nonpolar, no, the pQLaLparticles in the color and the polar
particles in the nail polish remover will attach themselves and as the nail
polish remover runs it will separate the colors out of the black.”

For a student who thought the unit was “difﬁcult to understand,” her
explanation of how chromatography works was quite accurate. The main
discrepancy was that she stated incorrectly that the markers were polar. She
eventually corrected herself when, later, I asked her whether water would
work to separate the colors of the T-Shirts. She responded, “No, because the
markers are nonpolar and water is polar. They (the colors in the markers)

only stick to stuff like nail polish remover and alcohol that are nonpolar.”

53

Initially when I asked Kari how salt dissolves in water, she replied, “I
don’t know.” Later, as she warmed up, I asked her what polarity has to do
with solutions. She responded, “If they are polar or nonpolar. If they’re
alike they’ll mix and if they’re not, they won’t. Like oil and water.” I asked
what makes two polar things mix in each other and she stated, “They have a
positive and a negative end so the positive end of one will hook to the
negative end of the other.” Then I went back to why does salt dissolve in
water and she said, “the positive end of the salt hooks to the negative end of
the water and it pulls it apart.”

In addition to her knowledge on polarity, solutions, and
chromatography questions, Kari remembered some things about emulsions,
problem solving, and determining the polarity of a molecule using Lewis
structures. These concepts were not remembered as vividly or as accurately.

I asked her how soap makes oil and water mix. She responded, “The
soap can hold on to the oil and allows it to all I remember about the soap
is that it sticks to dirt and it allows it to wash away because the water doesn’t
stick to the dirt because the dirt is nonpolar.” The demonstration performed
with oil, water, and soap could be part of the reason for this recollection.

In solving molarity problems, Kari’s memory deﬁnitely needed

refreshing. The concept of moles, molar mass, and molarity were only

54

vaguely familiar. After these concepts were reviewed, Kari’s recollection of
the units cancellation method of solving molarity problems returned. She
needed a little guidance on where to begin, but then solved the molarity
problems accurately. I asked her if using that problem-solving method
worked well for her and she said, “Yes, we used it in physics. Mr. D. didn’t
use it but we were like, ‘no, this is what we’re used to,’ so he used it. It
makes it easier.”

I asked Kari how we would determine whether a molecule was polar
or not (for example CH3C1.) She responded, “Don’t we draw dot
diagrams?” This was encouraging, yet she needed help in actually drawing
the Lewis structure for the example. The second example, CCl4, was
quickly solved correctly as nonpolar, “because it doesn’t have a positive and
a negative end.”

In addition to the two general chemistry students, I also interviewed
was my co-worker, “Ms M.” Ms M. and I do much of our chemistry
planning together so she was willing to teach the unit to her two chemistry
sections parallel to mine. Her comments before, during, and after the unit
proved beneﬁcial as did the formal interview with her. In general, Ms. M.’s
comments about the unit were extremely positive. She thought the

laboratory exercises and demonstrations were excellent motivators. When

55

asked speciﬁcally about the labs from the unit and their effectiveness both
motivationally and educationally, she had several comments.

“The labs were great. They tied into concepts as well as allowing the
kids to have a little bit of fun.” “The candy lab was really great and
straightforward and I think the kids really could grasp well the ideas that
dyes are used in different things. The added twist of the cancer preventing
agent put some reality in it.” “The T-shirt and the candy lab were both

really good authentic assessments.”

III. Data

The unit scores in reference to knowledge gained were indicative of
the success of the unit. The scores used to assess the knowledge gained by
the students were a pretest (Appendix C 1), the unit test average (one unit test
for H1 and H2, and two unit tests for I.C.,) the unit average (including labs,
homework, etc.,) and a posttest. As you can see in Figure 3, the LC. pretest
average was about 25 %, the unit test average was 77 %, the unit average
was 79 % and the posttest average was 60 %. The posttest for I.C.
(Appendix C2) was given about ten months after the conclusion of the unit,

during the following school year. The test was given to the students in two

56

 

Figure 4: H1 Assessment Results

57

 

Figure 5: H2 Assessment Results

Table 2: Percentage of Knowledge Retained

 

 

 

 

Unit Test Posttest Percent
(Averages) Retained
IC 77 60 78
H1 79 70 89
H2 8 l 73 9O

 

 

 

 

 

 

58

physics classes that had been in my chemistry classes the previous year.
Thirty-two of the original ﬁfty-seven students were retested.

Figures 3 and 4 show that the scores for leere similar to 1C. The
pretest average was slightly lower for H1 at 22 %. The unit test average was
79 %, the unit average was about 83 % and the post test average for H1 was
about 70 %. The posttest (Appendix C1) was given to the H1 students after
the next unit test, which was approximately two months later.

The scores for H2, other than the pretest, were slightly higher than
both of the previously reported groups (see Figure 5). The pretest average
was about 23 % but raised to about 81 % for the unit test average. The unit
average was about 85 % and the posttest (Appendix C1), again given after
the next unit test, was quite high at 73 %. The higher scores for this group
were not surprising, considering they were an advanced group.

In averaging all three groups, the increase from pretest to unit test was
about 56%. The amount of knowledge after the unit was taught should
deﬁnitely be higher than the prior knowledge, yet a gain of 56 % on average
is considerable. More signiﬁcant, I believe, is the post test score. The
students retained a considerable amount of information, from 2 months to 10

months after the unit was taught.

59

I determined the retention percentage for the study groups by dividing
each student’s posttest score by their unit test score. These percentages were
then averaged for each group. The posttest given to the students was not the
same as the unit test, but the content covered in each was similar enough, I
believe, to make a comparison for this calculation. In comparing the unit
test to the posttest, an impressive amount of knowledge was retained by the
students (Table 2). In the LC. group, the percent retained was about 75%.
In this group, not all the students were retested because the posttest was
given the following year to the students taking physics. The actual retention
might be slightly lower, based on the trend of higher ability chemistry
students proceeding to physics the next year. The H1 group had a retention
average of 88 %. The retention scores from the H2 group were even more
impressive, 96 %. The higher percentage retained from the two H groups

can be attributed, at least in part, to the timing of the posttest.

IV. Laboratory Assessment

Because I was particularly interested in laboratory exercises as key to
learning I also evaluated them. I compared the objectives I was attempting
to teach to the outcomes of the activities. I assessed the four main activities:

The Models of Covalent Compounds; T-shirt Chromatography; Extraction of

60

Candy Coatings; and The Effect of Temperature on Solubility. For all four
of the labs my objectives were similar. I wanted students to be able to:

acquire and develop laboratory skills speciﬁc to each activity;
draw conclusions based on observations;

improve comprehension of concepts covered in the unit;

apply information using analytical, creative, and critical thinking
skills; and

express a positive attitude toward the experience and science in
general

PPNT“

LII

These goals applied to all the labs, even though they were not all the
same style of exercise. Using Wilson and Stensvold’s (1993) deﬁnitions,
The Effect of Temperature on Solubility and The Extraction of Candy
Coatings can be considered conﬁrmation activities. The purpose of these
activities was to reinforce concepts of solubility and chromatography which
students were already familiar with. The Models of Covalent Compounds
exercise was a generalization activity where students were trying to build a
generalized explanation of how molecular structure affects polarity. The T-
shirt Chromatography lab most closely resembles a resolution activity, with
the students designing their own experiments to test the separating abilities
of different solvents with different inks.

Assessing the success of each activity was done in a few ways. Goal
#5, students expressing a positive attitude toward the exercise was evaluated

by observation. Throughout the laboratory experiments positive comments

61

were made and student involvement was 100%. For the T-shirt lab, some
students wanted to ﬁnish their shirts after school or at home, even though
there was no minimum requirement of decoration completion. Students also
enjoyed the Extraction of Candy Coatings. Students expressed that they
liked “playing with the model kits” during the Models of Covalent
Compounds exercise. They found that it helped them “. .. to picture the
structures easier.” Although the responses were not as enthusiastic, the
overall attitude during the Effect of Temperature on Solubility was also
positive. The students enjoyed watching for the crystals to “crash” out of
solution. Some heated the solution again to observe it a second time.

I evaluated goal #1 by monitoring the laboratory and assisting
students in manipulating equipment and performing procedures. For most of
the labs, the students were self-sufﬁcient and self-directed. In addition, the
Models of Covalent Compounds exercise was evaluated for the H1 and H2
groups by adding a lab practical to the unit test. Students had to construct a
given molecule with the model kit, draw the corresponding Lewis structure,
assign partial charges, and state whether the molecule was polar or non polar
and why. Of ﬁfty-two students tested, thirty-four scored 5 out of 5 or 100%
on this section. The overall average on the model construction portion of the

test was four point four out of ﬁve or 88%.

62

Assessing goals 2, 3 and 4 was more difﬁcult. The ability to draw
conclusions, improve comprehension, and apply information was most
easily evaluated by looking at how students answered questions about the
labs and concepts relating to them. In general, I was quite pleased with the
majority of the open-response questions all four of the labs. Students
comprehended a great deal of the content and most explained it well.

For example, students were asked “What factors affect how the components
of each ink separate?” in the post-lab of T-shirt Chromatography. Most
students were accurate with responses such as these.

“The factors that affected how the ink separated were the colors’
attraction to the solvent, the ink’s polarity and the solvent’s polarity.”

“What solvents you used, the amount of compounds in the ink and if
the polarities are Similar or not”(sic.)

“The number of compounds, the solvent, an the polarity differences
all affect how the components of each ink separate.”

Even the responses that were not completely accurate were close but
just not thorough enough. “What kind of alcohol you use with the color

,9

affects how the ink separates. “The type of alcohol used and the marker

type affect this.” “The solvent and the number of compounds” (sic.)

63

DISCUSSION AND CONCLUSIONS

There were several aspects of this unit that I felt were particularly
effective in conveying key information. The laboratory activities,
especially, were quite useful for the students to process and apply
information. “T-shirt Chromatography”, “Extraction of Candy Coatings”,
“Models of Covalent Compounds”, and “The Effect of Temperature on
Solubility” were four successful activities from this unit, as measured by
student interviews, teacher observations, and written responses in laboratory
reports.

The T-shirt exercise, I believe, was extremely effective. Both of the
students interviewed recalled it vividly, and also remembered the concepts
applied in the lab. When questioned, the students explained the reasoning for
the separation of colors at the molecular level. The student responses on
laboratory questions indicate that the principles of chromatography were
understood. I believe that if the students that were engaged in this exercise
were asked about chromatography a few years from now, they would
probably be able to recall the main concepts.

The T—shirt lab could be made even more effective with a few

changes. The activity calls for a pre-lab exercise of using different colored

64

inks and various solvents on ﬁlter paper to use as a test run before the T-
shirts. This step of the lab could be emphasized more and the students could
develop a more speciﬁc plan from this pre-lab. They could state a
hypothesis about speciﬁc inks and speciﬁc solvents that they are planning on
testing in the second part of the lab. Then a formal laboratory report could
be written, comparing the results of the inks on paper with those on the T-
shirts, rather than just answering the questions on the lab sheet. This would
allow the concept of the stationary phase to be investigated a little more
thoroughly. The main downfall to this idea is the amount of pens and
solvents used would be greater. Also, the ventilation must be very effective
or the students should work outside, as we did for the H1 group.

Another exercise that I feel worked well was the “Extraction of Candy
Coatings” chromatography experiment. The student involvement was quite
high in this lab. The students were working hard, but had few questions.
They seemed to enjoy working with a speciﬁc goal in mind: “ﬁnd the cancer
preventing yellow dye.” This gave a deﬁnite purpose to the exercise and
also enabled them to see a possible real-life application of the
chromatography concept.

When discussing with Ms. M. aspects of the unit that need

improvement or expansion, she felt that the candy chromatography

65

laboratory exercise could be expanded. One of the lab questions asks the
students if they think other substances might contain this yellow dye and
what they might be. One suggestion by Ms. M. was that we have a post-lab
exercise where students can test these predictions and see if, in fact, they do
contain the same yellow dye. The difﬁculty of this might lie in the
extraction process. Some research would need to be done to see of other
candies or food substances could be used in the same extraction process as
the M & M’s and Skittles.

Another exercise that I think was helpful to the students was the
“Models of Covalent Compounds” activity. Although this activity is not
quite as memorable as the previous two, it is effective, none the less. It
allows students to visualize atoms and molecules more easily than in
drawings or pictures. These kits assist students in learning how to make
Lewis structures of molecules. Later they can make these Lewis structures
without the kits. For my H1 and H2 group, I added a practical to the test.
Students had to construct a given molecule with the model kit, draw the
corresponding Lewis structure, assign partial charges, and state whether the
molecule was polar or non polar and why. As stated in the evaluation

section, the success rate of the evaluation was high.

66

The “Effect of Temperature on Solubility” lab exercise was another
effective task for the students. Before doing the exercise, the students had
been using solubility charts to answer questions such as how much
potassium chloride would dissolve in 100 g of water at 75 0C. In the
laboratory, they measured the solubility of ammonium chloride and used
their data to create their own solubility chart. They then answered questions,
using their own chart as well as a standard. This exercise was designed to
help them better understand what a solubility graph is and how the data on it
was determined. This activity makes charts and tables a little less
mysterious.

Although the areas of the unit covered by these four exercises were
well developed and effective, there are some areas that need some
improvement. The unit evaluation for H1 and H2 was quite comprehensive
and, I believe, needs to be separated into two, shorter tests or assessments.
The scores at I.C. where the unit assessment was divided into two are not
much different than H1 or H2, but the student apprehension was lower. For
the H1 and the H2 group, the students were quite nervous about the test
because, “so much has been covered since the last test.” Though the unit

seemed long to them, there are even more additions that could and should be

67

made that would lengthen it more. These supplements could not be added
without separating the assessment into at least two sections.

One such addition to the unit would be a lesson with a laboratory on
emulsions. The students were very interested in the concept of emulsiﬁers.
A laboratory experiment would capitalize on their interest and expand the
quality and quantity of information obtained and remembered about
emulsiﬁers and how they work.

Also, adding an exercise that would allow the students to use the
concept of molarity would greatly aid in their understanding. An activity
that might work involves having students make varying volumes of dilutions
of different molarities. Preparing these solutions might help make the
concept of molarity more tangible to the students. In addition, using a
tangible object to represent a mole and manipulating it with various volumes
might aid the students who have difﬁculty grasping derived units such as
molarity.

Overall, I was quite pleased with the effectiveness of this unit.
Having taught it three times, I modiﬁed it a little each time, continuing to
improve it. The success, I believe, is due to the thematic and hands-on
approach used throughout the unit. The concepts involved in polarity,

solutions and separation science are not easy ones for beginning chemistry

68

students to understand. Tying them together and showing their relevance to
each other by using good laboratory materials helps make the concepts a
little easier to grasp. When I was interviewing my co-worker, Ms. M., I
asked her what she thought of the thematic approach to this unit. She
replied, “It always seemed really disjointed teaching it separately. And from
all other texts that I’ve taught it which do separate all that stuff out, it was a
hard concept to grasp. So, even for me, it pulled it together more, teaching it
this way.”

In addition to the theme, the lab work was a large reason for the
success of the unit. The effectiveness of the laboratory exercises indicated
to me the importance of visual and tactile learning. The unit scores didn’t
necessarily reveal this to me. The students from all three groups scored
about the same as they did on previous units. What lead me to believe that
labs are so important were the student interviews, my observations of
students in class, and the students’ written responses to laboratory questions.
Before discussing the unit with students, I realized that labs were important.
Not until analyzing my results and interviewing students did I realize the
importance of a good lab in lab instruction. Not only does it help to engage
students with different learning styles, it helps to create a memorable

experience. When this memorable experience is recalled, with it comes the

69

information obtained from the experience. When returning from a vacation,
looking at the pictures you took brings back memories other than just those
on the pictures. Yet the pictures serve as a trigger, even years from now, for
the details from that vacation. I believe that laboratory experiences that are
well planned and coordinate with the concepts being taught provide this
same function. This realization will deﬁnitely affect my teaching as a
whole. Every unit will be planned with this approach, knowing how much

labs make a difference.

70

APPENDIX A

Activities, Experiments, and Demonstrations

l. The Models of Covalent Compounds

2. T-Shirt Chromatography

3. Chromatography Lab — Extraction of Candy Coatings
4. The Effect of Temperature on Solubility

5. Demonstration — Types of Mixtures

71

Appendix Al: The Models of Covalent Compounds

Introduction

Why should people care about the shapes of molecules? Consider that the properties of molecules,
including their role in nature, depend primarily on molecular structure or shape. Molecular shape
determines a compound’s boiling point, freezing point, viscosity and reactivity.

The molecular geometry of a molecule can be determined by examining the central atom and
identifying the number of atoms bonded to it and the number of unshared electron pairs surrounding it. The
shapes of molecules can be predicted by assuming the electron pairs around a central atom will position
themselves to allow for the maximum amount of space between them. Why would they do this?

Covalent bonds can be classiﬁed by comparing the difference in electronegativities of two bonded
atoms. The greater the difference, the more polar the bond. (When the difference gets greater than 1.67 the
bond becomes more ionic than covalent.) In a polar covalent bond, the electrons are more attracted to the
atom with the greater electronegativity, resulting in a partial negative charge on that atom. The atom with
the smaller electronegativity then acquires a partial positive charge.

Molecules made up of covalently bonded atoms can be either polar or nonpolar. The geometry of
the molecule contributes to the determination of whether it is polar or nonpolar. For example, if polar
bonds are symmetrically arranged around a central atom, their charges cancel each other and the molecule
in nonpolar. There are essentially no positive and negative poles or oppositely charged ends to the
molecule so therefor it is not polar.

Ball and stick models can be used to demonstrate the shapes of polar molecules. In this activity,
you will construct models of covalent molecules and predict the geometry of each molecule. (The shapes
will be one of the following types: Linear, Bent, Pyramidal, Tetrahedral, or Trigonal Planar.) You will
also draw electron dot structures, assign partial charges and predict whether the molecule is polar or
nonpolar.

Pre-Lab Discussion

1. What is a covalent bond?

 

 

2. What is a dipole?

 

 

3. What two factors determine whether a molecule is polar or not?

 

 

4. Calculate the electronegativity difference and predict the type of bond for the following examples:
(Use the electronegativity chart in your textbook as a reference.)

 

 

 

a. Na—Cl
b. C—H
c. S—O
d. N—N

 

72

Problem

How can the polarity of covalent molecules be predicted from their geometry and the types of bonds they
contain?

Materials
ball and stick model set
Procedure

1. Construct ball and stick models of the following compounds: (Remember each of the holes in each ball
will be ﬁlled if your model is correct.)

H2 HBr H20
NH, Cl—L I-lClO
N2 CHJNHZ CH3Cl
HZCO C2112 I-ICOOH
l-ICN

2. Set up a Data Table horizontally on a blank sheet of paper. Use the sample below as a reference for the
necessary headings. For each of the preceding compounds, complete the Data Table.

3. When you are ﬁnished, take apart your models and put them back in the box with all balls of the same

color together. Show your set to the teacher before placing it back on the shelf. Then answer the questions
at the end of the worksheet.

Sample Data Table: Structure and Polarity of Covalent Molecules

 

Formula Electron Dot Electronegmiv Difference Structural Formula Shape Molecular
Structure Bond Difference w/partial charges Polarity

 

 

 

 

 

 

 

 

 

 

 

73

 

Post Lab Questions

1. Explain how you used the molecular shapes to predict molecular polarity. Support your answer with
examples from the results of this investigation.

 

 

 

 

 

 

2. List the advantages and disadvantages of using ball and stick models to construct molecules.

 

 

 

3. Based on your results, predict the type of bonding, molecular geometry, and molecular polarity of the
following molecules:

a. HI

 

b. SClz

 

C. NH3

 

(1. C02

 

4. The polarity of a substance can have a great effect on its reactivity and solubility. A rough rule of
thumb for solubility is “like dissolves like.” Knowing this general rule, what can you predict about the
polarity of alcohol if you know alcohol dissolves water? Also, knowing that water alone will not
dissolve a greasy stain, what does that tell you about the composition of the stain?

 

 

 

Revised from:
“Models of Covalent Compounds,” Lab 22, Laboratory Manual, Chemistry: Connections to Our Changing
World, Upper Saddle River, New Jersey, Prentice Hall, 1996, pp. 117-120.

74

Appendix A2: T-shirt Chromatography

Introduction

In this lab you are going to experiment with different solvents to ﬁnd the best separation

techniques for the components of permanent inks. You will use a T-shirt (washed and dried, even if it’s
new) from home and create designs with different pens. Then, you will attempt to separate these inks into
their component colors with a variety of solvents. Before you start, you might wish to experiment with the
inks and solvents on ﬁlter paper in order to better predict the colors or patterns you will ﬁnd on your shirt.

Problem

How can you separate a mixture using chromatography?

Materials

permanent markers, several colors (Sharpies work great) ﬁngernail polish remover
T-shirt ethanol (30-50%)

coffee can ﬁlter paper

plastic pipet or eye dropper petri dish

2-propanol (30-50%)

Procedure

Filter paper extraction: (if desired)

1.

4.

Obtain a piece of ﬁlter paper and fold it in half. Create a wick by cutting two slits in the paper about 2
cm apart. Cut from the edge of the paper to the crease. Cut the wick in half.

Using the pen you wish to test, make a semi-circle with a radius of about 3 cm, across from the wick.
Let it dry and trace it again with the same pen to concentrate the ink.

Pour about 5 mL of the solvent you wish to use into the bottom of a petri dish. Place the ﬁlter paper on
top of the petri dish and bend the wick down so it is in the solvent. Put the top on the petri dish and
wait for the solvent to more toward the edge of the paper. Observe and record the colors extracted as
well as the pen and solvent used.

Repeat with as many of the pens and solvents you wish to test.

T-shirt Extraction

1.

Stretch a single thickness of cloth of your T-shirt over the top of the jar or can. Pull the cloth taut and
secure it with a rubber band.

Select a marker and make a pattern of dots or lines near the center of the stretched fabric.

Fill a dropper with the desired solvent and slowly drip it in the center of the fabric. Do not drip it on
your design, just near it. Continue dripping the solvent onto the cloth until the solvent has spread to
the edge of the can or jar.

Allow the wet section to dry.

Repeat steps 1-4 with each of the other markers, using different colored markers each time to make
another set of dots or patterns. Vary the solvent you use as well.

75

6. After all the chromatography patterns have developed, allow the T-shirt to dry completely.

7. Dispose of any excess solvent as directed by your teacher. Rinse out the can or jar with water. Clean
up your work area and wash your hands before leaving the laboratory.

8. At home, your can iron the T-shirt to help set the inks. For the ﬁrst machine washing, wash the T-shirt
by itself in cold water in case any of the inks run.

Data

Observations

 

Color of Pen Solvent Results

 

 

 

 

 

Questions

1. Why was it necessary to stretch the cloth taunt? What do you think would have happened if the cloth
had remained loose?

 

 

 

2. Which marker contained the greatest number of compounds? The fewest? How were you able to tell?

 

 

 

76

 

3. What factors affect how the components of each ink separate?

 

 

 

4. Overall, which solvent worked best for separation? Use your data to support your answer.

 

 

 

5. Predict what would have happened in the investigation if a polar solvent had been used.

 

 

 

6. Are “permanent” markers truly permanent? Explain.

 

 

 

7. Chromatography is often used to identify unknown compounds. Explain how this might be done.

 

 

 

Further Investigation

1. Cotton was used in this investigation. Find out if other fabrics work equally well. With the approval
and supervision of your teacher, try this investigation using swatches of rayon, wool, silk, or polyester.

2. Research the uses of chromatography in measuring and monitoring pollutants in air and water. Prepare
an oral report to present to your class.

Revised from:
“T-shirt Chromatography,” Laboratory Manual, Chemistry: Connections to Our Changing World, Upper
Saddle River, New Jersey, Massachusetts, Prentice Hall, 1996, pp. 235-238.

77

Appendix A3: Chromatography Lab—Extraction of Candy Coatings

Introduction

Fictional Scenario

The FDA just discovered that a certain yellow dye used in food coloring serves as a preventative
treatment for cancer. If maintained in a balanced diet, the consumption of a small amount of the dye daily
will prevent the onset of certain types of cancer. We were sent a sample of this yellow dye, but it is not
enough for the whole class to consume. The goal of this lab is to ﬁnd what candy might contain this dye,
then we can eat the candy and be saved from cancer. The candies available for testing today are Skittles
and M & M’s.

In this investigation you will use two separation techniques to determine the colors contained in
each of the dyes in candy coatings. In the ﬁrst part of the investigation, you will use wool yarn in a series
of chemical reactions to separate the dyes from sugar, chocolate, and other non-dye substances in the
candy.

In the second part of the investigation you will explore the makeup of the dyes by using a
separation technique called paper chromatography. In this technique a solvent dissolves the dyes and
canies them along a piece of ﬁlter paper. Different chemicals will have different rates of travel. You will
also run a chromatogram for the known yellow dye and compare results.

Pre-lab discussion

Read the entire laboratory investigation and the relevant pages of your textbook. Then answer the
questions that follow.

1. Write a hypothesis predicting which of the candies, if any, will contain the cancer preventing yellow
dye.

 

 

 

2. How are you going to test your prediction?

 

 

 

 

3. What is the chemical deﬁnition of a compound? A mixture?

 

 

 

 

78

4. How will a compound and a mixture behave differently in paper chromatography?

 

 

 

5. What causes separation of components in paper chromatography?

 

 

6. What does it mean to “decant” the liquid with the dissolved dye in it?

 

 

7. What is the purpose of the paper wick?

 

 

Problem

Which Skittles and M & M’s contain the same yellow dye as the ﬁctional cancer preventing yellow dye?

Materials

Part A

safety glasses

laboratory apron

hot plate

60 cm wool yarn

beaker, 150 mL

tap water

4 small candies each of three
different colors

3 large test tubes

test tube rack

Part B

micropipet

ﬁlter paper, 11 cm diameter
scissors

ruler

graduated cylinder, 10 mL
distilled water

acetic acid, 3M

6 small test tubes

tongs

stirring rod

paper towel

ammonia water, 1%

3 watch glasses

graduated cylinder, 10 mL
developing solution

4 petri dishes and covers
4 toothpicks

79

Safety

Wear your safety and lab apron at all times during the investigation. Never eat any foodstuffs in

the laboratory. Acetic acid and ammonia can irritate or burn your skin. Do not rub your eyes or touch your
skin without ﬁrst washing your hands. If these solutions contact your skin or clothing, wash the area with
large amounts of water and notify your teacher.

The solutions used in Part B are extremely ﬂammable. Be sure there are no burner ﬂames in the

laboratory. Turn off the hot plate during Part B. Be sure to keep your petri dishes covered when the
chromatogram is running to minimize fumes in the laboratory.

Procedure

PartA

l.

10.

11.

Put on your goggles and lab apron. Fill a 150 mL beaker one-third full of tap water and place it on the
hot plate. Turn on the hot plate and start the water to boil. Meanwhile, place four small candies of the
same color in a large test tube. Place four of a different color in another test tube and four more of still
another color in your third test tube.

Pour 7 mL of distilled water into each test tube with the four candies. Add 3 drops of concentrated
acetic acid to the water-candy mixture. CAUTION: Concentrated acetic acid can irritate or burn
your skin. If you spill any, rinse the aﬂected area immediately with large amounts of cold water and
report the spill to your teacher.

When the colored coating dissolves, slowly pour, or dccant, the liquid dye ﬁom each large test tube
into three small test tubes. Make sure the candy or any other solid residue remains behind in the large
test tube. Discard the candy and other solid residue into a paper towel and then into the garbage. DO
NOT POUR THE CANDY CLUMPS INTO THE SINK!

Using a stirring rod, add a 20 cm piece of woolen yarn and 3 drops of concentrated acetic acid to each
liquid-dye mixture.

Place the test tubes into the boiling water bath for about 5 minutes or until most of the dye becomes
absorbed by the yarn.

With test tube tongs, take the test tubes out of the boiling water and place them in the test tube rack.
CAUTION: Never touch hot glassware with your bare hands. Remove the yarn from the test tube
with the stirring rod. Rinse the yarn under tap water for about 1 minute. This removes the remaining
acid so that the ammonia base can work completely.

Pour 5 mL of ammonia water into each of three small clean test tubes. CAUTION: Avoid breathing
the ammonia vapors. Submerge the rinsed yarn into the ammonia water.

Place the test tubes with the yarn and the ammonia water in the boiling water bath for about 5 minutes
or until most of the dye from the yarn has dissolved in the ammonia-water solution. The solution
should turn the color of the dye. Remove the yarn with a stirring rod and rinse with water. Put the
yarn in a paper towel and dispose of it in the waste basket.

Use tongs to remove the test tubes containing the ammonia-water-dye solution from the beaker of
boiling water. Pour each dye solution into a watch glass.

On a piece of white paper, write your group names and hour and place it on a designated area of the
side counter. Carefully move the three watch glasses and set them on the white paper until tomorrow.

Dispose of the excess acid solution in a container provided by your teacher. Save the ammonia

solution and put it in your drawer. Clean up your work area and wash your hands before leaving the
laboratory.

80

PartB

12.

13.

14.

15.

16.

17.

18.

Put on your goggles and lab apron. Retrieve your watch glasses from the side counter. If all the liquid
evaporated, add 3-5 drops of the ammonia-water solution in each glass and swirl carefully to dissolve
the dye into solution.

Obtain a piece of ﬁlter paper and fold it in half. Unfold the paper and cut a 2 cm wide wick in the
paper by making two cuts ﬁ'om the edge to the crease in the middle. Your ﬁlter paper with wick
should look like the ﬁgure below. Do this with three more pieces of ﬁlter paper to end up with one
chromatography set for each dye you extracted plus one for the ﬁctional cancer preventing yellow dye.
Label each ﬁlter paper in pencil near the cut line for the dye your will be separating on that paper.
Also, draw a line in pencil across from the wick, parallel to the crease. This will be the “starting line”
for the dye.

or...

 

 

Dip the end of a toothpick into one of your dye solutions and make a very small spot of dye on the
ﬁlter paper where the wick meets the rest of the paper, behind the line you drew. Using three more
toothpicks, do the same with your other two dyes and the yellow sample from your teacher. Allow the
spots to dry. Repeat at least ﬁve times on the same spot to concentrate the dye on the ﬁlter paper.
Make the spots as small as possible. Record the initial color of the spots.

Using a graduated cylinder, measure and pour 8 mL of the developing solution into the bottom half of
each of four petri dishes.

Cut the wick in half crosswise and bend it down to make a stand. Place it into the developing solution,
as shown below. Carefully place the odrer half of the petri dish over the ﬁlter paper, not allowing the
wick to be crushed or ﬂattened. Allow to develop for about 30 minutes, making observations.

Observe how far your dye traveled ﬁ'om the original spot and mark the outer limit of the solvent with
pencil.

Dispose of all your solvents as directed by your teacher. Clean up your work area and wash your
hands before leaving the laboratory.

 

/ﬂlm
mm“
m Ian—H
m mm .

81

Data Table 1

 

Sample 1

Sample 2

Sample 3

Yellow Dye

 

Type of Candy

 

Color of Candy

 

Initial Color of Spot

 

Observations During

Separation

 

Final Color of Spot

 

Colors Present Aﬁer

Developing

 

Distance Traveled

by Solvent

 

 

Distance Traveled

by Dye

 

 

 

 

 

Complete the following data table by pooling your data with that of other students in the class.

 

 

 

 

 

 

 

 

 

 

 

 

 

Data Table 2

Type of Candy Color Component Colors Compound or Mixture?
M & M’s blue
M & M’s green
M & M’s red

M & M’s orange
M & M’s brown
M & M’s yellow
Skittles purple
Skittles red
Skittles orange
Skittles green
Skittles yellow

 

 

 

 

82

 

 

Questions

1. Which dyes tested were compounds? Which were mixture? How could you tell?

 

 

2. Why was it important to keep the spot applied to your ﬁlter paper as small as possible?

 

3. What would have happened if the entire ﬁlter paper and not just the wick had sat in the developing
solution?

 

 

4. Which candy(ies) did you determine had the same yellow dye as the known cancer preventative?
How did you come to this determination?

 

 

 

 

5. Was your hypothesis of which candy contained the yellow dye correct or incorrect?

 

6. What other sources can you think of that might contain this yellow dye? Justify why you think these
products might contain it.

 

 

 

7. Do you think the coatings of the candies you tested are make with the same type of food coloring sold
in grocery stores? How could you test your hypothesis?

 

 

 

83

Chromatography Lab — Extraction of Candy Coatings — Teacher Preparation

This lab is designed to be used during a unit on solutions, but could be used when discussing the
differences between compounds and mixtures. The concepts of polarity and “like dissolves like” are
applied using chromatography. The lab ﬁts nicely into two class periods, but the students have to be ready
to start immediately on the ﬁrst day.

Materials (15 lab groups)

PART A PART B

45 large test tubes, 18x150 (a little smaller work as well) 15 micropipets (or one in the NH3)
M & M’s and Skittles (one lb. of each was plenty for 4 classes) 60 pieces of ﬁlter paper,
ll-cm di.

15 test tube racks scissors

15 graduated cylinders, 10 mL 60 petri dishes

375 mL distilled water rulers

30 mL acetic acid, 3.0 M in dropper bottles pencils

90 small test tubes, 13 x 100 mm 300 mL developing solution

1 skein of white wool yarn teacher prepared “cancer-

15 hot plates (or burners and ring stands) preventing” dye(see below)

tap water

15 pairs of tongs or forceps

15 stirring rods

300 mL ammonia water (NH3, 1%)

45 watch glasses or evaporating dishes

To make “cancer-preventing” dye:

Follow the procedures in the student lab for extracting the color from the candies using three sets
of yellow Skittles. This should be plenty for four or ﬁve classes, especially if you supervise the dispensing
of it.

To make Ammonia-Water: To Make Developing Solution:
l0% by volume household ammonia 57% by volume butanol
90% by volume distilled water 15% by volume household ammonia

14% by volume distilled water
14% by volume methanol

*Store both solutions in containers with screw caps. Do not work near any heat sources.

Additional Tips:

Make sure the students mark a line in pencil on the ﬁlter paper to indicate the initial location of the
dye. They need to do this before the extraction begins. (It is not in their directions.) Also, they should
draw a line aﬁer the chromatogram is ﬁnished at the leading edge of each color extracted and at the solvent
edge. The solvent edge is especially important to do on day 2 because the next day the edge will not be
visible anymore.

In order in ensure all colors are tested, it is a good idea to assign them the day before. (No one
seems to want to do the brown M & M and it has the greatest separation!)

Revised from: “Candy Coatings: Compounds or Mixtures?”, Chemistry: Connections to Our Changing

World Laboratory Manual, Upper Saddle River, New Jersey, Needham, Massachusetts, Prentice Hall,
1996, pp. 35-40.

84

Appendix A4: The Effect of Temperature on Solubility

Introduction:

Hot tea can dissolve more sugar than iced tea, and warm water dissolves less oxygen than cold
water. The maximum amount of any solute that can dissolve in a given amount of solvent is called its
solubility, and this depends on temperature.

The solubilities of gases always decrease with increasing temperature. For liquids and solids,
solubilities generally increase with increasing temperature, as is the case with sugar in tea. However, there
are a number of exceptions to this, two examples being cerium sulfate, Cez(SO4)3, and lithium carbonate,
LiZCO3. For these ionic solids, solubility decreases with increasing temperature.

In this activity, you are to determine the effect of temperature on the solubility of ammonium
chloride, NH4CI, in water. After collecting data at various temperatures, you will plot the data to produce a
solubility curve showing how the solubility of ammonium chloride varies with temperature. This, then can
be used to predict the solubility at other temperatures.

Purpose:
How does the solubility ammonium chloride in water vary with temperature?
Materials:
Apron and safety goggles Ring stand, ring, and wire gauze
Four medium-sized test tubes Laboratory burner and matches
Test tube rack Thermometer
Grease Pencil Ammonium chloride (NI-14Cl)
One lO-mL graduated cylinder Medicine dropper
Filter paper Glass stirring rod
Spatula Supply of ice
Balance Graph paper
Procedure:

*Before beginning, read throughout the entire lab, then set up a data table.
*Wear goggles and aprons.

1. Obtain four medium-sized test tubes, a test-tube rack, and grease pencil. Label the test tubes
1 through 4, respectively.

2. As accurately as possible, determine the mass of a piece of weigh paper. Record the value in
the data table. Use this weigh paper on the balance when measuring out your Nl-LCI.

3. To each of the test tubes, 1 through 4, you want to add samples of NH4CI having the
following masses: 3.5 g, 4.5 g, 5.5 g and 6.5 g. It is not necessary that your samples be
exactly these masses; it is necessary that the values be within 0.05 grams, and that you
determine the masses as accurately as possible. Use a spatula to add or remove small amounts
of the solid from the weigh paper. Record the mass values in the data table.

4. Fill a 400-mL or 600-mL beaker about three-fourths full with water to use as a hot-water bath.
Place the beaker on a piece of wire gauze on a ring clamped to a ring stand. Place a
thermometer in the water and begin heating while you proceed to step 5. The goal is to heat
the water to 90°C.

5. Put 10.0 mL of distilled water in a lO-mL graduated cylinder. Use a medicine dropper to

bring the bottom of the meniscus right to the 10.0 mL line. Add this water to test tube 1.
Repeat this procedure, adding 5.0 ml. of water to each of the test tubes.

85

Post lab

1.

2.

Stir each of the test tubes with a glass stirring rod, rinsing and drying the stirring rod in
between each solution. There will probably be solute remaining in test tubes 2, 3 and 4.
Place all three test tubes in the hot water bath.

While test tubes 2-4 are heating up, place test tube 1 in a beaker containing ice water. Place
the thermometer in the test tube and observe. When crystals ﬁrst appear, note the temperature
of the solution.

Take test tube 2 out of the hot water bath and observe. If all the solute is gone, place the
thermometer in the test tube and hold up to a light. Watch for the very ﬁrst signs of
crystallization, and then immediately note the temperature. If crystallization begins too
quickly, or you do not catch it the instant it begins, redissolve the precipitate and repeat until
you are able to determine the temperature at which crystallization begins. Record this in the
data table.

Repeat step 8 for test tubes 3 and 4. If necessary, stir the mixtures with a stirring rod to make
all the solute dissolve before beginning crystallization.

Change data to grams NILCI per 100 grams of H20. (Assume the water is 1.0 g/1.0 mL.)

Graph this data. Make g NILCI/ 100g H20 the y axis and temperature, 0 to 100, the x axis.
Use graph paper.

Using your extrapolated graph, how much NH4CI could dissolve in 100g of H20 at 100°C?
Using the Handbook of Chemistry and Physics, ﬁnd the solubility of NH4C1 at 100°C.

Calculate the percentage error between your experimental value (#3) and the
theoretical value (#4).

Calculate the molality (moles solute/kg of solvent) of each sample.

86

Appendix A5: Demonstration — Types of Mixtures

Materials:

4 large test tubes
vegetable oil
table sugar
isopropyl alcohol
magnesium oxide
tap water

Procedures:

Mix a small amount of each of the ﬁrst four substances listed with a small amount of water in each
of the four test tubes. Put the following terms on the board for the students to see: solute, solvent,
miscible, soluble, insoluble, immiscible, and suspension. Have the students describe, on paper, each of the
four mixtures using as many of the terms as possible. After they have attempted this, discuss the meaning
of these words by explaining what happened in each test tube.

87

APPENDIX B

Quiz and Unit Tests

1. Molarity and Solubility Quiz
2. LC. Unit Test #1 — Polar Molecules and Chromatography
3. LC. Unit Test #2 — Solutions and Colloids

4. H1 and H2 Unit Test

88

Appendix B1: Molarity and Solubility Quiz

NAME

 

Using the solubility chart provided, answer questions 1-3.

I. At what minimum temperature will 60.0 grams of NH,C1 dissolve completely?

2. How much RbCl will dissolve at 80°C?

3. If 120 g of LiCl is dissolved in 100 g of H20 at 90°C and is cooled to 20°C, how much precipitate will
be formed?

4. What is the molarity of a solution containing 15.6 g of List., in 200 mL of solution?

5. How many grams of KCl are required to make 250 mL of a 0.350 M solution?

6. How many mL of solution are required to use 44.6 g of LiCl to make a 1.75 M solution?

7. Calculate the molarity of a 7500 mL of solution containing 2515 g of NaNO3.

89

Appendix B2: I.C. Unit Test #1

Name

 

Unit Test #1 -- Polar Molecules and Chromatography

10.

ll.

12.

13.

Substances composed of nonpolar molecules are generally

a. solids b. molecular solids

c. liquids with high boiling points d. gases

The of a dipole can be described by its dipole moment.

a. strength b. length c. polarity (1. duration
bonds, unless symmetrically arranged, produce polar molecules.

a. Sigma b. Covalent c. Polar d. Pi

Atoms covalently bonded with differences in electronegativity will have large polarity.

a. large b. small

force is the type of van der Waals force which exists between two nonpolar molecules.
a. Dispersion b. Dipole-dipole c. Intramolecular d. Induced dipole

A bond in which one of the atoms attracts the shared pair of electrons more strongly than does
the other is a(n) bond.
3. nonpolar covalent b. metallic c. polar covalent d. ionic

Which of the following covalent bonds would be the most polar? (The electronegativity
values are as follows: h, 2.20; C, 2.50; N, 3.07; CI, 2.83; O, 3.50.)
a. H-C b. H-N c. H--Cl d. H-O

As the dipole moment increases, the strength of the forces between the molecules
a. varies at random b. increases c. decreases d. remains constant

Weak forces that may hold molecules to each other are termed
a. covalent bonds b. van der Waals forces
c. resultant forces d. coordinate bonds

A nonpolar molecule that has had its electron cloud distorted by the proximity of a polar
molecule is called a(n)
a. dipole b. complex ion c. isomer d. induced dipole

In chromatography, the mixture to be separated plus the liquid or gas in which it is dissolved
is known as the

a. substrate b. ﬁltrate c. dispersion medium d. mobile phase

Chromatography is an example of .
a. fractionation b. precipitation c. segmentation d. allocation

A convenient method for the separation of substances based on differences in polarity and
attraction for a medium is called

a. distillation b. fractional crystallization

c. chromatography (1. ﬁltration

90

14. Which of the following is a separation technique used to analyze volatile liquids by
employing an inert gas as the mobile phase?

a. column chromatography b. paper chromatography c. gas chromatography
15. Which of the following types of particles would interact to produce a dipole-induced dipole

force?

a. two polar molecules b. one polar and one nonpolar molecule

c. two nonpolar molecules d. two polyatomic ions

16. Which of the following bonds is the least polar? (The electronegativities are as follows:
C, 2.50; O, 3.50; CI, 2.83; Si, 1.74; N, 3.07)
a. C--O b. O--Cl c. Si--O d. N--O

17. Among molecules of comparable molecular mass, as the dipole moment increases, the boiling
point of the substance .
a. varies at random b. increases
c. decreases d. remains the same

18. Which of the following forces is the greatest contributing factor to van der Waals forces?

a. dipole-dipole b. dispersion c. dipole-induced dipole d. intramolecular
19. As the dipole moments of molecules of comparable mass increase, their melting points

a. increase b. decrease

c. remain the same d. increase and then decrease

Match the descriptions in Column I with the proper type of chromatography in Column 11.

Column 1 Column 11
a. Solvent moves on strip by capillary action. 20. thin layer
b. Varying amounts of contamination in helium 21. column
produce varying amounts of electric current
22. paper
c. A glass plate is coated with packing.
23. gas

d. A sample in solution is added to the tube containing
packing material

Draw Lewis structures for each of the following molecules, label partial charges, and determine whether
each is polar or nonpolar.

24. CH3Br 25. H1

26. NH3 27. H20

91

28. Arrange the following types of substances in order of increasing boiling points. Put a one (1)
below the substance with the lowest boiling point, a two (2) under the second lowest and a three
(3) under the substance with the highest boiling point.

noble gas atoms polar molecules nonpolar molecules

Fill in the blanks correctly. Use each of the listed words once.

chromatography dipole polar bond
induced dipole van der Waals forces fractionation
dispersion forces

 

 

 

29. __ is a method of separation based on adsorption.
30. __ are weak forces that may hold together groups
of molecules.
31. __ is the overall process of separating parts from a whole.
32. A(n) _ is a molecule that has temporarily become a dipole

because of the presence of another nearby dipole.

 

33. A(n) is a covalent bond in which one atom attracts the
shared pair more strongly that the other.

 

34. A(n) is a molecule with unsymmetrical
charge distribution

 

35. result from temporary dipoles.

 

Answer each of the following:

36. Describe one of the experiments you did and how chromatography was used. Use the terms stationary
phase and mobile phase in your description.

92

37. The solvents used in the T-shirt lab smelled up the lab. How is this evidence of their degree
of polarity?

38. How is it possible to have a nonpolar molecule that contains polar bonds? Explain and give
an example.

39. Explain how two completely nonpolar substances can be attracted to each other enough to turn into a
liquid. (Liquid nitrogen for example.) Discuss the forces involved in this attraction.

93

Appendix B3: I.C. Unit Test #2

Name

 

Unit Test #2 — Solutions and Colloids

10.

11.

In a solution, the substance being dissolved is the
a. solvent b. solute c. mole fraction (1. hydrate

The most common solvent is
a. alcohol b. benzene c. water Cl. acetone

The process by which solvent molecules surround solute particles is
a. efﬂorescence b. solvation c. displacement d. deliquescence

Which type of substance will probably dissolve in a nonpolar substance?
a. nonpolar b. polar c. ionic d. metallic

The attachment of water molecules to dissolving molecules and ions is

a. hydrationb. dissociation c. hydrogenizing d. synergy

A carbonated soft drink is an example of which type of solution?

a. liquid solute and liquid solvent b. gaseous solute and liquid solvent
c. liquid solute and solid solvent (1. liquid solute and gaseous solvent

Ethylene glycol (antifreeze) and water are completely miscible. If you mix 20 cm’ ethylene

glycol with 10 cm3 of water in a graduated cylinder, you would expect to see

a. one homogeneous solution

b. a mixture with a distinct boundary layer one-third of the way from the bottom of the
cylinder

c. a mixture with a distinct boundary layer two-thirds of the way from the bottom of the
cylinder

d. a mixture with a diffuse boundary layer one-half of the way from the bottom of the
cylinder

A solution in which an undissolved substance is in equilibrium with the dissolved substance
is called a(n)

a. dilute solution b. supersaturated solution

c. saturated solution (I. unsaturated solution

Which of the following would not affect the rate of solution of a solid in a liquid?
a. heating the solution b. shaking the solution
c. grinding up the solution d. increasing the pressure on the solution

The solution process of most solids is
a. endothermic b. exothermic c. isothennic d. unrelated to temperature

The study of the properties of matter whose particle size in at least one dimension lies
between 1 nm and 100 nm is

a. nuclear chemistry b. colloid chemistry

c. physical chemistry (1. analytical chemistry

94

12. Which of the following combinations would most increase the solubility of a gas in a liquid?
a. increase the pressure and decrease the temperature
b. increase the pressure and increase the temperature
c. decrease the pressure and decrease the temperature
(1. decrease the pressure and increase the temperature

13. The concepts of molarity and molality are alike in that both .
are based on the total volume of the solution

express the amount of solute in moles

are mass/mass relationships

are volume/volume relationships

999'.”

14. Which of the following is a comparison of moles of solute to moles of solution?
a. molarity b. molality c. percent by mass d. mole fraction

15. A crystal of copper sulfate is added to copper sulfate solution. After 15 minutes, the crystal
is observed unchanged in the bottom of the solution. On the basis of this observation, the
solution is best described as
a. supersaturated b. dilute c. saturated d. unsaturated

 

l6. Mayonnaise is an example of a liquid dispersed in a liquid and is therefore classiﬁed as a(n)

a. emulsion b. gel c. aerosol d. sol

 

17. Small drops of wax dissolved faster in hexane than a block of wax would because the drops
of wax have more
a. polarity b. energy c. surface area (1. enthalpy of solution

18. Which of the following explains the ability of water to dissolve ionic substances?
a. There are two hydrogen atoms for every one oxygen atom.
b. Hydrogen and oxygen are covalently bonded.
c. Oxygen has six electrons in its outermost energy level.
(1. Water molecules are polar.

19. The addition of 1, crystals to water is an example of
a. polar solvent - polar solute b. polar solvent - nonpolar solute
c. polar solute - nonpolar solvent (1. nonpolar solvent - nonpolar solute

Match the description of the solutions with the correct concentrations.

20. 4 moles of solute in 2 dm3 of solution (a) 4 molar
21. 2 moles of solute in 4 kg of solvent (b) 2 molal
22. 2 moles of solute in 0.5 dm3 of solution (c) 2 molar

23. 2 moles of solute in 1 kg of solvent ((1) 0.5 molal

95

1n the following table, indicate (yes or no) if a solution would be likely to occur.

Solute type Solvent type Does solution occur?
24. polar nonpolar __
25. nonpolar nonpolar __
26. polar polar __
27. nonpolar polar __

28-31 Explain why the above solutions occur or don’t occur.

32-34 You are given three aqueous mixtures and told that one is a suspension, one is a solution,
and one is a solution, and one is a colloid. Describe what steps you would follow to
determine which mixture is which.

35-37 You are given a solution of salt water that could be saturated, unsaturated, or
supersaturated. Describe how you would determine which of the three solutions this is.

38-41 Calculate the number of grams of solute needed to make 250 cm3 of 0.3 50M NaZSO.
solution.

96

42-45 Calculate the molarity of a solution containing 10 grams of NaOH in enough water to form
600 cm3 of solution.

46-49 49.0 grams of H280. are added to 250 grams of water. Calculate the molarlity of this
solution.

50-53 Calculate the mass of solute needed to add to 500 g of H20 to make a 0.35m SnBr,
solution.

54-57 Calculate the mole fraction for each component in a solution containing 45.0 g of

97

Appendix B4: H1 and H2 Unit Test

Name

 

Unit Test — Solutions, Polarity, and Chromatography

l.

10.

ll.

12.

13.

Substances composed of nonpolar molecules are generally

a. solids b. molecular solids c. liquids with high boiling points d. gases
The of a dipole can be described by its dipole moment.
a. strength b. length ‘ c. polarity d. duration

In a solution, the substance being dissolved is the
a. solvent b. solute c. mole fraction (1. hydrate

The most common solvent is
a. alcohol b. benzene c. water (I. acetone

The process by which solvent molecules surround solute particles is
a. efﬁorescence b. solvation c. displacement d. deliquescence

bonds, unless symmetrically arranged, produce polar molecules.

a. Sigma b. Covalent c. Polar d. Pi
Atoms covalently bonded with differences in electronegativity will have large polarity.
a. large b. small c. zero

A bond in which one of the atoms attracts the shared pair of electrons more strongly than does
the other is a(n) .

a. nonpolar covalent bond b. metallic bond

c. polar covalent bond d. ionic bond

Which type of substance will probably dissolve in a nonpolar substance?
a. nonpolar b. polar c. ionic d. metallic

The attraction of solvent molecules to solute particles and the consequential separation of the
solute is called
a. hydration b. dissociation c. hydrogenizing d. solvation

A carbonated soft drink is an example of which type of solution?
a. liquid solute and liquid solvent b. gaseous solute and liquid solvent
c. liquid solute and solid solvent d. liquid solute and gaseous solvent

Dry cleaners use tertachloroethylene, C2C14, to dissolve oil, grease, and alcohol because

C2C14 .
a. is soluble in water b. dissolves ionic compounds
c. is a polar molecule (1. is a nonpolar molecule

Which of the following combinations would most increase the solubility of a gas in a liquid?
a. increase the pressure and decrease the temperature
b. increase the pressure and increase the temperature
c. decrease the pressure and decrease the temperature
d. decrease the pressure and increase the temperature

98

14.

15.

mill-1001'.)

The concepts of molarity and molality are alike in that both .
a. are based on the total volume of the solution. b. are mass/mass relationships
c. express the amount of solute in moles . d. are volume/volume relationships

If an ink separates into two or more colors using chromatography, the ink must be .
a. a mixture b. a compound c. an element d. nonpolar

 

 

m "-1
16. In Figure 11-1, the solubility of NaNO; increases by approximately g per 100 g of
water when the water’s temperature rises from 10°C to 90°C.
a. 50 b. 80 c. 120 d. 160
17. In Figure 11-1, heating a saturated solution of LiZSO4 in 100 g of water from 10°C to 90°C

18.

19.

20.

would result in .

a. 5 additional grams of LiZSO. going into solution
b. 80 additional grams of Lizso. going into solution
c. 5 additional grams of U280. leaving the solution
d. no change in U280. concentration

InFigure 11-1, wouldbeunsaturated.
a. 40 g ofKCl in 100 g ofwater at 80°C

b. 40 g of NaCl in 100 g of water at 90°C

c. 145 g of NaNO; in 100 g of water at 45°C
d. 105 g obeCl in 100 g ofwater at 45°C

A crystal of copper sulfate is added to a copper sulfate solution. After 15 minutes, the crystal
is observed unchanged in the bottom of the solution. On the basis of this observation, the
solution is best described as .

a. supersaturated b. dilute c. saturated d. unsaturated

Particles in an emulsion are

a. smaller that the particles in a suspension

b. larger than the particles in a suspension

c. smaller than the particles in a solution

(1. the same size as the particles in a suspension

99

21.

22.

23.

24.

25.

Adding lecithin to an oil-water mixture .
3. causes the oil and water to separate b. changes the oil into soap
c. prevents the water from evaporating d. keeps the oil and water mixed

Which of the following covalent bonds would be the most polar? (The electronegativity
values are as follows: H, 2.20; C, 2.50; N, 3.07; CI, 2.83; O, 3.50).
a. H--C b. H--N c. H--Cl d. H-O

A convenient method for the separation of substances based on differences in polarity and
attraction for a medium is called

a. distillation b. fractional crystallization

c. chromatography d. ﬁltration

Among molecules of comparable molecular mass, as the dipole moment increases, the boiling
point of the substance
a. varies at random b. increases c. decreases (1. remains the same

The addition of [2 crystals to water is an example of .
a. polar solvent -- polar solute b. polar solvent - nonpolar solute
c. polar solvent -- nonpolar solute d. nonpolar solvent -- nonpolar solute

Match the description of the solutions with the correct concentrations.

26. 4 moles of solute in 2 L of solution (a) 4 molar
__ 27. 2 moles of solute in 4 kg of solvent (b) 2 molal
__ 28. 2 moles of solute in 0.5 L of solution (c) 2 molar
__ 29. 2 moles of solute in 1 kg of solvent (d) 0.5 molal

In the following table, indicate (yes or no) if a solution would be likely to occur.

Solute type Solvent type Does solution occur?
30. polar nonpolar __
31. nonpolar nonpolar __
32. polar polar ____
33. nonpolar polar __

34-37. Explain why each of the above solutions occur or don’t occur.

100

38-40 You are given a solution of salt water that could be saturated, unsaturated, or supersaturated.
Describe how you would determine which of the three solutions you have.

41-42 What characteristics make soap a good emulsifying agent?

43-44 Why is detergent a better choice than soap for laundering with hard water?

45-47 What factors should be considered before taking vitamin supplements? Why?

101

48-50 Calculate the number of grams of solute needed to make 250.0 mL of a 0.350M NaZSO4 solution.

51-53 Calculate the molarity of a solution containing 10.0 grams of NaOH in enough water to form
600.0 mL of solution.

54-56 How many mL of solution can be made by using 73.6 g of Mg(NO)3 to make a 0.25 M solution?

57-59 What is the molarity of a solution that contains 22.5 mg of SnBrz dissolved to make 25 mL of
solution?

60-64 Describe how you would prepare 1500 mL of a 0.50 M solution of Cu(SO4)2.

102

Model Construction

FORMULA Name

 

After receiving a formula from your instructor, go to an unoccupied lab station where you will ﬁnd a model
kit. Assemble your model, answer the following questions, and LEAVE your assembled compound AND
this sheet at the lab station. Return to your desk and complete the rest of your test.

Questions

1. Draw the electron dot diagram (Lewis dot structure) for your compound.

2. Assign partial charges to the above diagram.

3. Is your compound polar or nonpolar? Why?

103

APPENDIX C

Pretest, Posttests, and Survey

1. Pretest, I.C., H1 and HZ; Posttest H1 and H2
2. Posttest LC.

3. Survey H1 and H2

104

Appendix C 1: Pretest 1.C., H1 and H2; Posttest H1 and H2

Name

 

Date Class Hour

 

1. How is boiling point related to bond strength?

2. What is a polar covalent bond?

3. What is chromatography?

4. If you wanted to separate two polar substances in a dye, what type of solvent would you try?

5. What is the difference between a solute and a solvent?

6. What determines whether two substances will dissolve in each other?

7. What is an emulsiﬁer? Give an example of one, if you can.

8. How does a detergent work?

9. Is CHC13 a polar molecule? Why or why not?

10. Is CC], a polar molecule? Why or why not?

11. What are some applications for chromatography?

105

Appendix C2: I.C. Posttest

10.

11.

Name

 

In a solution, the substance being dissolved is the
a. solvent b. solute c. mole fraction d. hydrate

The most common solvent is
a. alcohol b. benzene c. water d. acetone

The process by which solvent molecules surround solute particles is
a. efflorescence b. solvation c. displacement d. deliquescence

Which type of substance will probably dissolve in a nonpolar substance?
a. nonpolar b. polar c. ionic d. metallic

The attachment of water molecules to dissolving molecules and ions is

a. hydrationb. dissociation c. hydrogenizing d. synergy

A carbonated soft drink is an example of which type of solution?

a. liquid solute and liquid solvent b. gaseous solute and liquid solvent
c. liquid solute and solid solvent (1. liquid solute and gaseous solvent

Ethylene glycol (antifreeze) and water are completely miscible. If you mix 20 cm3 ethylene

glycol with 10 cm’ of water in a graduated cylinder, you would expect to see

a. one homogeneous solution

b. a mixture with a distinct boundary layer one-third of the way from the bottom of the
cylinder

c. a mixture with a distinct boundary layer two-thirds of the way from the bottom of the
cylinder

(1. a mixture with a diffuse boundary layer one-half of the way from the bottom of the
cylinder

A solution in which an undissolved substance is in equilibrium with the dissolved substance
is called a(n)

a. dilute solution b. supersaturated solution

c. saturated solution d. unsaturated solution

Which of the following would not affect the rate of solution of a solid in a liquid?
a. heating the solution b. shaking the solution
c. grinding up the solution (1. increasing the pressure on the solution

The solution process of most solids is
a. endothermic b. exothermic c. isothennic d. unrelated to temperature

The study of the properties of matter whose particle size in at least one dimension lies
between 1 nm and 100 nm is

a. nuclear chemistry b. colloid chemistry

c. physical chemistry d. analytical chemistry

106

14.

15.

16.

17.

18.

Which of the following combinations would most increase the solubility of a gas in a liquid?
a. increase the pressure and decrease the temperature

b. increase the pressure and increase the temperature

c. decrease the pressure and decrease the temperature

d. decrease the pressure and increase the temperature

The concepts of molarity and molality are alike in that both
a. are based on the total volume of the solution

b. express the amount of solute in moles

c. are mass/mass relationships

d. are volume/volume relationships

Which of the following is a comparison of moles of solute to moles of solution?
a. molarity b. molality c. percent by mass d. mole fraction

A crystal of copper sulfate is added to copper sulfate solution. After 15 minutes, the crystal
is observed unchanged in the bottom of the solution. On the basis of this observation, the
solution is best described as

a. supersaturated b. dilute c. saturated d. unsaturated

Mayonnaise is an example of a liquid dispersed in a liquid and is therefore classiﬁed as a(n)

a. emulsion b. gel c. aerosol d. sol

 

Small drops of wax dissolved faster in hexane than a block of wax would because the drops
of wax have more
a. polarity b. energy c. surface area d. enthalpy of solution

Which of the following explains the ability of water to dissolve ionic substances?
a. There are two hydrogen atoms for every one oxygen atom.

b. Hydrogen and oxygen are covalently bonded.

c. Oxygen has six electrons in its outermost energy level.

d. Water molecules are polar.

The addition of 1, crystals to water is an example of
a. polar solvent - polar solute b. polar solvent - nonpolar solute
c. polar solute - nonpolar solvent d. nonpolar solvent - nonpolar solute

Match the description of the solutions with the correct concentrations.

20.

21.

22.

23.

4 moles of solute in 2 dm3 of solution (a) 4 molar
2 moles of solute in 4 kg of solvent (b) 2 molal
2 moles of solute in 0.5 dm3 of solution (c) 2 molar

2 moles of solute in 1 kg of solvent (d) 0.5 molal

107

In the following table, indicate (yes or no) if a solution would be likely to occur.

Solute type Solvent type Does solution occur?
24. polar nonpolar __
25. nonpolar nonpolar __
26. polar polar __
27. nonpolar polar __

28-31 Explain why the above solutions occur or don’t occur.

32-34 You are given three aqueous mixtures and told that one is a suspension, one is a solution,
and one is a solution, and one is a colloid. Describe what steps you would follow to
determine which mixture is which.

35-37 You are given a solution of salt water that could be saturated, unsaturated, or
supersaturated. Describe how you would determine which of the three solutions this is.

38-41 Calculate the number of grams of solute needed to make 250 cm’ of 0.350M NaISO,
solution.

108

42-45 Calculate the molarity of a solution containing 10 grams of NaOH in enough water to form
600 cm3 of solution.

46-49 49.0 grams of H280, are added to 250 grams of water. Calculate the molarlity of this
solution.

50-53 Calculate the mass of solute needed to add to 500 g of H10 to make a 0.35m SnBr,
solution.

54—57 Calculate the mole fraction for each component in a solution containing 45.0 g of

Comments:
What do you remember most about the solutions, polarity, and separation science unit? What did you
learn? Describe.

109

Appendix C3: Survey, H1 and H2

Answer the following questions honestly. Circle the number, 1-5, which best indicates your opinion.
1 - highly disagree 2 - disagree 3 - indifferent 4 - agree 5- highly agree
1. I found this unit to be organized. l 2 3 4 5

2. 1 found the labs helped my understanding of the

material 1 2 3 4 5
3. I found it easy to make connections and draw

conclusions between polarity and chromatography. 1 2 3 4 5
4. I found the labs tied in well with the instruction. 1 2 3 4 5
5. I found the labs motivated me to learn the material. 1 2 3 4 5

6. The demonstrations proved beneﬁcial in
understanding concepts. 1 2 3 4 5

7. My understanding of the material is this chapter is
greater than material from previous chapters. 1 2 3 4 5

8. I understand the effect polarity has on whether or
not a solution will occur. 1 2 3 4 5

9. I understand the difference between a polar covalent
bond and a nonpolar covalent bond. 1 2 3 4 5

10. I understand how an emulsiﬁer works. 1 2 3 4 5

l l. I understand the difference between a detergent
and a soap. 1 2 3 4 5

12. I understand the practical applications of
chromatography. 1 2 3 4 5

l3. I understand how electrons could be shared
unequally in a covalent bond. 1 2 3 4 5

14. I understand how molecular geometry is used

to determine molecular polarity. l 2 3 4 5

Cements:

110

Please comment on the organization of the polarity/solutions/separation science thematic unit. Did you
ﬁnd it easy to make connections? Draw conclusions? Etc.?

Discuss the helpfulness of the labs and demonstrations in this unit. Did they tie in with the instruction?
Did they add to your understanding? Motivate you to learn? Etc.?

How did your understanding in this unit compare to previous units? How did your scores compare?

Please comment, in general, on my teaching style. What things work for you, what doesn’t? Feel free to
make suggestions on areas for improvement.

111

LITERATURE CITED

112

LITERATURE CITED

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Brownstein, E.M. & Destino, T. (1995). Scenes from an African American Saturday Science Program.
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Crawley, F .E., Barufaldi, J .P., & Salyer, BA. (1994). Coordinated Thematic Science in the Classroom: A
View from Pilot Teachers. School Science and Mathematics, 94(5), 240-247.

Garnett P.J. & Tobin, K., (1988). Teaching for Understanding: Exemplary Practice in High School
Chemistry. Journal of Research in Science Teaching, 26(1), 1-1

Glasson, GE. (1989). The Effects of Hands-on and Teacher Demonstration Laboratory Methods on
Science Achievement in Relation to Reasoning Ability and Prior Knowledge. Journal of
Research in Science Teaching, 26(2), 121-131.

Grifﬁths, A.K. & Barry, M. (1993). High School Students’ View About the Nature of Science. School
Science and Mathematics, 93(1), 35-37.

Hofstein, A. & Lunetta, V.N. (1982). The Role of the Laboratory in Science Teaching: Neglected Aspects
of Research. Review of Educational Research, 52(2), 201-217.

Huheey, James (1983). Inorganic Chemistry: Principles of structure and reactivity. New York:
Harper & Row.

Lehman, JR. (1990). Students’ Verbal Interactions During Chemistry Laboratories. School Science and
Mathematics, 90(2), 142-150.

Stohr, RM. (1996). An Analysis of Frequency of Hands-On Experience and Science Achievement.
Journal of Research in Science Teaching, 33(1), 101-109

Tamir, P. (1989). Training Teachers to Teach Effectively in the Laboratory. Science Education, 73(1),
59-69.

Tobin, K. (1990). Research on Science Laboratory Activities: In Pursuit of Better Questions and Answers
to Improve Learning. School Science and Mathematics, 90(5), 403-417.

Wilson, J .T & Stensvold, MS. (1991). Improving Laboratory Instruction: An Interpretation of Research.
Journal of College Science Teaching, 29(5), 350-353.

Wilson, J .T. & Stensvold, MS. (1993). Using Three Types of Outcomes to Design Laboratory Activities.
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Yager, R.E. & Lutz, M.V. (1994). Integrated Science: The Importance of “How” Versus “What”. School
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113

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