The Joys of Sound and Light in the Laboratory
Demonstrations and Class Experiments
Irwin Talesnick
57 Glen Cameron Road, Unit 6
Thornhill, ON, CANADA, L3T 1P3
Voice
FAX
e-mail
905 709 2033
905 709 2040
[email protected]
TABLE of CONTENTS
Experiment No.
Experiment Title
Experiment No. 1
Experiment No. 2
Experiment No. 3
Experiment No. 4
Experiment No. 5
Experiment No. 6
Experiment No. 7
Experiment No. 8
Experiment No. 9
Experiment No. 10
Experiment No. 11
Experiment No. 12
Experiment No. 13
Experiment No. 14
Experiment No. 15
Experiment No. 16
Experiment No. 17
Experiment No. 18
Experiment No. 19
Experiment No. 20
Experiment No. 21
Experiment No. 22
Experiment No. 23
Experiment No. 24
Experiment No. 25
Experiment No. 26
Experiment No. 27
Experiment No. 28
Experiment No. 29
Experiment No. 30
Experiment No. 31
Experiment No. 32
Table of Contents
Introduction - For the Love of Science and Sciencing
Demonstrations and the Art of Demonstrating
My Philosophy
The Role of the Laboratory in Teaching and Testing
Electrochemical (Orange Juice) Clock
The Characteristics of Life
Floating Cans
Hydrogen Chlorine Explosion
Electrochemical Flashbulb
Hydrogen Organs
Combustion of Hydrogen
Combustion of Hydrogen & Hydrocarbons in Chlorine
Eudiometers
Combustion of Methanol
Combustion of Magnesium
Aquarium Analogy - Two Aquaria
Aquarium Analogy - One Aquarium
Electrical Cells
Electrolysis of Sodium Sulfate Solution
Parallel and Series Circuits – Electrical Unknowns
Flashing Lights – Exercises in Model Building
Experiments in Electrical Circuitry
Rolling Spheres Down an Inclined Plane
How Airplanes Stay Afloat
Levitation and the Gas Bag or "Move a Refrigerator”
Shapes of Carbon Compounds
Molecular Shapes and Bonding (VSEPR Theory)
Thermometers and Their Use
Unknown Samples
Spectral Emission
The Oscillating Clock Reaction
Blue Bottle Experiment
Conductivity of Acids and Bases
Photochemical Reduction of Thionine
Equilibrium Constant NO2 – N2O4
Shell Game
Page No.
1
3
5
8
10
15
19
20
22
23
25
26
26
27
28
29
30
31
32
34
36
37
41
43
44
44
45
46
46
47
47
48
50
51
51
52
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Experiment No. 33
Experiment No. 34
Experiment No. 35
Experiment No. 36
Experiment No. 37
Experiment No. 38
Experiment No. 39
Experiment No. 40
Experiment No. 41
Experiment No. 42
Experiment No. 43
Experiment No. 44
Experiment No. 45
Experiment No. 46
Experiment No. 47
Experiment No. 48
Experiment No. 49
Experiment No. 50
Experiment No. 51
Experiment No. 52
Experiment No. 53
Experiment No. 54
Experiment No. 55
Experiment No. 56
Experiment No. 57
Experiment No. 58
Conductivity of a Solid
Conductivity of a Gas
Ripping Cans
Reaction of Aluminium with Copper(II) Chloride
Surface Tension
Bottles and Caps - An Analogy to Stoichiometry
Equilibrium in Cu(2+) (aq) Solutions
Temperature Equilibrium Tubes – Commercial
Preparation of a Brown Gas
Temperature Equilibrium (N02 – N2O4) - Home Made
Colorimetry
Reaction of Solution s A & B….Equilibrium in Aqueous Solution
Vapor Pressure in a Separatory Funnel
Safety Tips
Supersaturation
Mass of a Plastic Bag - Empty and Full
Preparation of a Gas Bag Assembly
Mass of a Syringe-Full of Gas
Use of the Vari-Stop Syringe - for all Experiments
Pressure - Volume Relationships in Gases
Pressure - Temperature Relationships in Gases
Partial Pressure of a Gas in a Fixed Volume
Effect on Pressure of Adding Liquid to a Gaseous System
Effect of Temperature on Vapor Pressure – Qualitative
Effect of Temperature on Vapor Pressure – Quantitative
Effect on Vapor Pressure of Adding Liquids to System
Diagrams
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53
54
54
55
55
56
56
57
58
58
59
59
60
60
62
62
63
64
65
66
67
68
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For THE LOVE of SCIENCE and SCIENCING
Demonstrations and the Art of Demonstrating
As I prepare to write about Demonstrations and the Art of Demonstrating I cannot help but comment
on the large number of “Hands-On” books that have come on the market in the last few years. Long
may they prosper. Only outstanding demonstrations should displace “Hands-On” activities.
This outline is being written both for use in the many lectures and workshops that I present at
conferences, in-service teacher meetings, and pre-service teacher meetings, as well as for the many
practicing teachers who write and ask for demonstration and laboratory ideas and suggestions.
Incorporated in the materials are instructions and guidelines for the use of many pieces of equipment
that I have designed and produced.
During the course of this write-up I will try to outline some of the teaching strategies that I use when
performing particular experiments as demonstrations in a regular classroom. I will discuss many of
the concepts and experiments both from the viewpoint of the science teachers as well as from the
viewpoint of the science students. Please feel free to interrupt with questions or comments at any
time. If any questions or comments come to you when you are back at your school please feel free to
call or write. I will try to assist in any way that I can.
I will try to give credit for ideas that I have borrowed from others over the past 45 years, but
sometimes I do not know where the ideas came from. If you see something that you wrote, or that you
told me about, please let me know. Thank you for your help these many years.
I have used many of these demonstrations, hands-on experiments and activities with students from
Kindergarten - College, and with teachers in varied settings. I will try my best to outline how and
when I have used each of these activities.
Please remember that the best way to improve your teaching is to borrow and use ideas from all
sources. Ideas do not have to be original, but they must be safe, useful and interesting. Again, I would
like to thank all of those wonderful teachers and colleagues from whom I have borrowed. I hope that
over the years you have been repaid for your willingness to share.
The subject areas and grade levels at which these activities can be used are at the discretion of the
teacher. Many of the activities were written for high school chemistry classes, but they are definitely
not limited to that use. Feel free to revise and adapt - to add and to subtract. Let me know if you have
any suggestions for improving or adapting any of the activities.
Following is the description of the complete WORKSHOP KIT that I have distributed at my Full Day
workshops. We can, if you wish, use any part or parts of the kit. You have to decide how much you
want to spend per participant.
The workshop kit contains the materials required to make the equipment for many of the experiments
that are performed during the full day workshop. The charge for the workshop kit is $100.00 (US) per
participant. The total retail value of the kit is approximately $200.00. The kit is available only to
workshop participants. It is not available for general purchase by anyone.
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1 set of instructions and guidelines
6 plastic stop cocks
5 syringe extenders (luer lock connectors)
1 role of transparent, adhesive metric tape
1 bag of 10 shared pair balloons
1 bag of 10 UNSHARED PAIR balloons
1 140 mL plastic syringe (drilled)
1 20 mL plastic Vari-Stop syringe
1 20 mL plastic syringe
1 replacement gasket for the 140 mL syringe
1 clock, hands and hardware (1.5 volts)
1 clockface (symbols of the elements)
1 set of copper, zinc and magnesium electrodes
10 electrical leads, with alligator clips
1 conductivity of solids kit
1 9 v battery
1 battery clip
1 strip of insulated sockets
4 6.3 volt bulbs
3 LEDs
1 gas pressure gauge
2 short lengths of rubber tubing
1 ungraduated thermometer
1 screw mount syringe lock
1 large nail for use with 140 mL syringe
1 set of 8 SAFETY Tips
Participants will see immediate applications to their classroom and laboratory programs. Many of the
experiments will be taken from Chemistry, but some examples will be drawn from each of Physics and
Biology. This is done because some teaching techniques can be illustrated easily with examples from
the other areas of science.
All of the experiments in this workshop are designed to introduce, and/or reinforce specific concepts
in the sciences. Many of the activities are in the areas of the gas laws, acid-base, equilibrium, redox,
electrochemistry, and parallel and series circuitry. Most of the activities involve the use of simple and
inexpensive equipment and materials. Participants will be given directions to build many of the
inexpensive devices.
Participants will perform, observe, discuss and take part in more than 40 experiments (IN THE FULL
DAY WORKSHOP) that are designed to interest, motivate, question and challenge the participants,
and ultimately, their students. Participants will be encouraged to adapt the experiments for use in their
own classrooms, both in teaching and in testing. The role of evaluation in the teaching process will be
continually emphasized. Participants will have opportunities during the day, to examine a large
collection of popular reference books containing a variety of demonstrations and laboratory activities
in each of the sciences.
Equipment and Supply Requirements
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I will bring much of the special equipment. You will only have to supply some common materials that
are available in any reasonably well equipped laboratory. Once we settle on the “curriculum” I’ll send
a list of my requirements.
Materials to Provided by the Host
2 pieces of dry ice, each with minimum dimensions, 20 cm x 20 cm x 5 cm (approximately)
2 pieces of (water) ice, each with minimum dimensions, 20 cm x 20 cm x 5 cm (approximately)
500 mL of each of concentrated Nitric, hydrochloric and sulphuric acids
2 overhead projectors
5 kg of ice cubes
2 electrical extension cords
projection screen (or white wall)
5 L distilled water
multiple outlet power bar
For a very large room you might want TO provide a wireless microphone, video camera and projector.
My Philosophy……
1. Demonstrations can and should be fun for both the students and the teachers, but fun must not be
the only objective. Each of the demonstrations must be used to illustrate or introduce an important
concept.
2. I usually prefer to have students perform their own “Hands-On” activities rather than have them watch
demonstrations.
3. The demonstration route should be followed only if the members of the class cannot perform the
experiment themselves because of factors that are beyond the control of the teacher. Factors such as
safety considerations and/or the expense and availability of materials are legitimate reasons for
replacing class experiments with teacher performed demonstrations.
4. One common reason given for performing demonstrations in the classroom is that "it saves valuable
time." This argument can be used to justify the neglect of demonstrations as well as the neglect of
classroom experiments.
A second commonly used reason (excuse) is the high cost of materials. I firmly believe that many
classroom demonstrations and experiments can be done effectively with low cost as well as household
or local store bought materials. The secret of saving money is ingenuity.
6. A further reason might be the lack of dialogue among students during certain student performed
experiments. This can be, and is sometimes, a legitimate reason for doing a demonstration instead of a
class experiment. I often use this reason to perform demonstrations in place of or in addition to
student performed classroom experiments.
If you must do a demonstration please do it well. Prepare the materials carefully and rehearse the
steps in the procedure, and the dialogue that you will use, prior to the execution of the demonstration.
Remember that there are some steps that are better done before the students arrive in class. Your
students will appreciate the experience and your extra effort so much more.
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The preparation and rehearsal are necessary regardless of how many times you have already
performed that demonstration. I cannot begin to count the number of times I have changed a
demonstration during a pre-class tryout. There are many variables that can and do go wrong; they
must be checked each time.
Something unexpected does not have to spoil an otherwise “perfect” demonstration. Note that the
unexpected can also add to the effect of the demonstration.
There are a variety of teacher rules as well as student rules that the capable teacher will put in place
whenever demonstrations are performed. The teacher rules must take account of student safety as well
as personal safety AT ALL TIMES. I will attempt to introduce and emphasize the appropriate
SAFETY considerations whenever appropriate.
Chemistry teachers would be well advised to read George Atkinson's PROVOCATIVE OPINION
column in the December 1985 (page 1070) issue of The Journal of Chemical Education. Most
experiments as well as most chemicals can be safety hazards, if not used correctly and with respect.
Teachers should NOT avoid ALL "potentially hazardous" materials without thinking about the context
and safety considerations in advance. Always look to better and safer ways of doing laboratory work.
Many of the experiments that are described in this handout were, at one time, done with materials that
are not presently allowed in most classrooms or laboratories. Today the materials used are as safe as
they can be.
The demonstrations and classroom experiments that we will do and discuss will all be in accord with
the rules of good laboratory procedures, safety for teachers and students as well as with good teaching
in mind. Each of the demonstrations will focus on a particular concept, fact or idea.
There are many "Don't" as well as "Do" items that must be taken into account while the teacher is
performing demonstrations. Some of the Do and Don't suggestions are listed:
Do
have all materials carefully prepared and labeled!
Do
try the experiments out before class!
Do
ask relevant questions!
Do
have student assist in many of the activities!
Do
require that students make notes or answer questions!
Do
know why the demonstration is being performed!
Do
emphasize and respect safety! You and your students must
wear safety glasses at ALL times during ALL Lab activities!
Don't
Don't
Don't
Don't
Don't
Don't
leave dirty equipment and glassware for others to clean up!
use materials that someone else has prepared for a class!
use a demonstration to use up some unplanned free minutes!
use upper grade experiments simply to entertain junior grades!
give the answer away before the experiment is performed!
waver on safety!
Demonstrations need not be complex; the equipment need not be expensive. In many cases
demonstration equipment can be made from junk and easily obtained inexpensive materials. The
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experiment must work and a point must be made. If you use the lab safely and thoughtfully then both
you and your students will enjoy and profit from the experiences that you share.
THE ROLE OF THE LABORATORY IN TEACHING AND
TESTING
The construction of laboratories for students in elementary, junior high and, secondary schools, as well
as in colleges and universities requires the outlay of a very considerable amount of money. In addition
to the construction costs one must add in the costs of maintenance and the supplies and equipment that
must be purchased, replenished and replaced on a regular basis. Is this money well spent? Are the
additional funds required for safety equipment, both personal and for the building, a worthwhile
investment? There are many questions that have been raised about the appropriateness of spending so
much money on facilities that are used only rarely. Can the same topics be taught without using
laboratory facilities? Many colleges and universities have replaced their first year laboratory programs
with computer simulations, movies and tutorial sessions. Are these procedures as effective and as
interesting as laboratory activities?
How often, and for what reasons are these facilities used? Do we need student laboratory benches and
services in addition to demonstration equipment and facilities? The questions related to the
appropriateness of the allotment of resources, financial and space, as well as human, to the laboratory
can only be answered after we consider some of the reasons why laboratory work is performed in the
classroom. Why do we want our students to be familiar with laboratory procedures? It seems that they
can learn many of the chemical principles that we want to teach them without incurring the time,
expense and DANGER of performing individual laboratory activities.
Some of the questions that must be asked are:
1) What skills do we want students to develop?
2) Are laboratory skills of value to students who study advanced courses in Chemistry (science)?
3) Are laboratory skills of value to students who do NOT study advanced courses in Sciences?
4) Do students enjoy laboratory work?
5) Can students afford the time to perform laboratory work?
6) Do teachers enjoy laboratory work?
7) Do teachers have the time to prepare the laboratory exercises?
8) How do we evaluate student performance in the laboratory?
9) How do we evaluate student achievement as the result of laboratory work?
10) How do we incorporate the result of laboratory evaluation into the determination of overall
student success in the chemistry program?
11) How does the amount of lab work by students correlate with success on standardized tests?
There are many answers to each of these questions. The answers given by specific students and
teachers must be considered in line with the way in which their overall achievement in Chemistry
(science) is evaluated. The students I surveyed indicated that they enjoyed performing laboratory
work and that they also appreciate the meaningful way in which their laboratory work was evaluated.
The formats generally used for evaluating laboratory work are:
1) Collect and grade written laboratory reports in which the students write answers to questions,
and perform specified calculations.
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2) On a test or quiz assign calculations and questions that are similar to those that the student has
already answered in a laboratory report.
3) Observe the students in a lab setting and assign a grade based on their interest and industry.
Each of the three formats that I have indicated are useful in determining how much information the
student has retained, or whether or not the student is able to perform specific calculations. None of the
three formats takes into account or measures the students' skills in performing specific laboratory
operations nor do these methods evaluate the students’ appreciation of the role of the laboratory in
designing the solutions to chemical problems.
In this session we will examine and design some examples of problems that students can be asked to
solve in order to evaluate their understanding of the process involved in using the laboratory skills that
they have practiced. We will examine a number of methods of grading students on their ability to
design and then perform laboratory activities in response to specific problems. The problems can be
designed in such a way that there are a number of different answers to each one. The student can then
be evaluated on his/her creativity as well as laboratory dexterity.
In order to evaluate students on their ability to solve problems they must have had experience in
solving a number of problems during the teaching/learning process in regular lab classes. I believe
that the proportion of the marks assigned to students for actual laboratory work must be equivalent to
the proportion of class (course) time that was spent on laboratory work. In most cases this will mean
that the actual laboratory mark will be a significant part of the mark assigned in the course.
For each unit, or sub-unit, of the course some of the objectives must be:
1) The students will know how to perform laboratory operations.
2) The students will know how to apply laboratory skills to specific problems.
3) The students will understand the nature of the problem solving process.
For each unit, or sub-unit, of the course some of the performance criteria must be:
1) The students will be able to design and perform an experiment to answer a specific question.
2) The students will be able to design and perform an experiment to measure a specific quantity.
3) The students will be able to design and perform an experiment to identify a specific material.
In ALL cases student evaluation must be related to the ways in which they were taught. Students who
have been drilled on the solution of numerical (chemical) problems will score better on this type of test
than students who have performed and designed many experiments, but have not been drilled on
numerical problem solving. Conversely, students who have had experience in performing and
designing many laboratory experiments will out perform students, who have not had these
experiences, on laboratory based tests.
The choice is yours....Please make it carefully.
Experiment No. 1
ELECTROCHEMICAL (Orange Juice) CLOCK
MATERIALS
1 clock mechanism
1 clock face
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1 “pizza” box
1 carton of orange juice
1 plastic cup
1 roll two-sided tape
2 electrical leads with alligator clips
1 set of hardware
(brass washer, brass nut, 1/4", brass nut, 1/8", rubber washer)
1 set of clock hands (hour hand, minute hand, second hand)
1 set of electrodes: rectangular copper foil, rectangular zinc foil, magnesium coil on a coffee stir stick
CLOCK ASSEMBLY
1. Mount the clock face directly onto the bottom face of the “pizza” box. A hole through which the
clock will be mounted has already been drilled, both in the box and in the clock face. The clock
face should be oriented so that the letters Li are closest to the open side of the box, and Mg will be
closest to the top of the box.
2. Use transparent plastic tape to secure the clock face to the “pizza” box.
3. Open the small plastic bag (with the nuts and washers) over a tray so that these small items are not
accidentally lost.
4. Place the black rubber washer (ring) over the stem of the clock mechanism.
5. Open the “pizza” box and pass the stem of the clock through the hole in the box and the hole in the
clock face. When secured, the clock mechanism and the rubber washer will be inside the box.
6. Place the brass washer over the stem of the clock mechanism
7. Secure the clock mechanism in place with the large brass nut. Tighten the brass nut as securely as
possible. It may be necessary to use a pair of pliers, or a wrench, to complete the process. Put
your hand inside the box, and hold the clock in position while tightening the brass nut.
8. Position the hour hand so that the stem of the clock passes through the hour hand. Push the hour
hand down over the stem of the clock. The hour hand will slide part way down, over the upper
part of the clock stem.
9. Position the minute hand so that the stem of the clock passes through the minute hand.
10. Secure the minute hand in position with the small brass nut.
11. Secure the second hand in position. The protruding rod in the stem of the clock mechanism fits
into the hole in the back of the second hand. Make sure that the second hand is secured firmly to
the clock stem.
12. Take note that the symbols + and - appear in the diagram of the battery that is shown in the battery
slot of the clock. Clip one lead to each of the terminals marked + and -. Take note of which lead
is connected to the + terminal, and which lead is connected to the - terminal.
13. Position the box so that it can be seen by the observers. The box should be stood on its end so that
the clock face is facing the observers.
14. Use a short piece of the two-sided carpet tape, to secure the cup to the table top, immediately
beside the box.
15. It is a good idea to clean the electrodes before each use. Immerse the copper and magnesium
electrodes in a cup of vinegar for a few seconds. You will observe bubbles forming on the
magnesium and the surface will appear bright and shiny. Remove both the copper and the
magnesium from the vinegar and rinse the electrodes with water.
16. Mount the copper electrode in the cup. The copper electrode is already cut so that it can be hooked
over the rim of the cup. Adjust the length of the copper electrode by folding over the bottom end
of the copper foil.
17. Unwind one loop of the magnesium electrode and hook it over the rim of the cup. Take care that
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the copper and magnesium electrodes do not touch each other.
18. Connect the free end of the lead connected to the + terminal on the back of the clock to the copper
electrode.
19. Connect the free end of the lead connected to the - terminal on the back of the clock to the
magnesium electrode.
20. Adjust the time on the clock face to the time that the demonstration is scheduled to be performed.
21. At the appropriate time open a new carton of orange juice and pour it into the cup. The clock
should start running.
22. I always use a new carton of juice so that the students know that the juice has not been tampered
with. It is very important, from the point of view of safety, that only a new carton of juice is
tasted.
NOTE:
The zinc electrode can be used to “see” what difference it makes if it is used in place of
either the copper or the magnesium electrode.
IMPORTANT
Be sure to check the operation of the clock before each use.
Place the copper electrode in a cup of vinegar.
Connect the copper electrode to the lead connected to the + terminal of the clock.
Connect the magnesium electrode to the lead connected to the - terminal of the clock.
Dip the magnesium electrode into the vinegar; the clock should start.
Remove the magnesium electrode from the vinegar quickly; it will be consumed if you leave it in the
vinegar.
You will have to obtain a roll of magnesium ribbon from a chemical supply company in order to
replace the magnesium electrode. During operation of the clock the magnesium is oxidized. The
magnesium will be consumed, and the clock will stop.
USE and OPERATION of the CLOCK in CLASS
1.
2.
Encourage your students:
to ask questions about the clock and its operation. Do not answer their questions .
to design experiments to answer their own questions.
to construct models to explain how and why the electrochemical clock works.
Some typical questions that I will answer are:
What are the metals in the cell?
I answer this question because they cannot see and determine which metals are being used in
the cell.
Can you drink the juice after the clock is operated?
Emphatically NO! You cannot eat or drink any laboratory materials .
Is there a battery in the back of the clock?
I open the box so that they can see the back of the clock and the empty battery cavity.
Some of the questions that are most frequently asked by both teachers and students are:
1. Will the clock work?
2. Why does the clock work?
3. What was in the cup before the orange juice was added?
Answer - air and the electrodes.
4. What are the electrodes?
Answer - Magnesium and Copper.
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5. What are the electrodes connected to?
Answer - The clock mechanism.
6. Is there a battery inside the box?
7. What is inside the box?
Answer - Show the inside of the box
8. Can I drink the juice after the experiment?
Answer - No! (In a very loud voice)
9. How long will the clock run?
10. Does the clock keep good (correct) time?
11. Can other juices be used to run the clock?
12. Can other liquids (other than juices) be used to run the clock?
13. What is the effect of increasing / decreasing the temperature of the liquid?
14. What is the effect of increasing / decreasing the concentration of the solution?
15. What happens if the electrical connections are reversed?
16. Can other metals be used as the electrodes?
17. Can non-metals be used as the electrodes?
18. Can more than one clock be operated, at the same time, off the same beaker of juice?
19. What voltage is being generated?
20. Should the extra clocks be connected in parallel or in series?
21. Can other appliances (pieces of equipment) be operated by the cell?
22. What is the foam on top of the orange juice?
23. Has the orange juice been changed during this process?
24. What is the significance of the letters on the clock face?
25. Are the symbols of the elements arranged in any particular pattern?
26. Why are we doing this exercise?
27. Where can I get one of those clocks?
28. Where can I get a copy of the clock face?
Some students appear to become frustrated when I respond to their questions by saying:
"How would you find out?”
“Design an experiment to answer your question(s)."
The frustration level is decreased when they prepare the materials and try some of the experiments that
they designed.
SAFETY CONSIDERATIONS: All experiments must be cleared by the teacher before students are
allowed to proceed with laboratory work. There are some activities that students might try at home.
Additional Notes
These clocks do not run backwards; the leads must be connected correctly.
I generally use a second clock on an overhead projector so that it can be seen in all parts of the
classroom, and also so that other questions can be raised during the demonstration.
As the class is ready to start I open a carton of orange juice and ask a student to taste and identify the
contents.
I then walk over to the clock and pour the juice into the beaker holding the electrodes.
The class is usually quite surprised that the clock starts to run.
Students immediately ask a series of questions, all of which I acknowledge, but only three of which I
answer.
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I write all of the questions on the board so that we can refer to them later. I actively encourage the
students to continue asking questions until I have at least 25 questions listed on the board. They are
usually quite concerned that even at this point I do not offer answers to them. The intent of the
exercise is to arouse their curiosity and to have them design and do experiments. The clocks are
reasonable enough that I can provide a number of them for use in my classroom.
The questions are not listed in the order in which they have been asked in any specific session. I can
never predict the order. After listening to and recording all the questions I ask the class to select those
that they want me to try to answer.
Each of the questions leads, or can lead, to a series of laboratory activities and a number of different
chemical concepts that can be discussed. I can see how this one short experiment will be repeated a
number of times during the course; each repetition will be used to introduce and/or reinforce a
different idea. With one exception (Question 26) all of the questions make me happy and proud to be a
chemistry teacher. If question 26 is asked in a group of teachers I become saddened. The question
implies that we are wasting time. It implies that any content that might be taught could be taught more
efficiently or effectively by telling the students that magnesium metal is being oxidized to magnesium
ion.
Questions 27 and 28 re-establish my faith in the profession of chemistry teaching and the
professionalism of so many (the majority of) chemistry teachers. Imagine the joy in my heart when,
on the day following an in-service workshop in Scarborough, Ontario, a young science teacher (Dave
Doucette) telephoned me and reported that he had done the ORANGE JUICE CLOCK
demonstration with his class of Grade 10 Basic Level science students and they had responded
enthusiastically. Imagine my additional joy when I received photocopies of the reports and
experimental designs that were written by these students.
These are just some of the questions students ask. Try this experiment. You and your students will
like it.
There are many other activities that can be carried out as well. Can you join a number of these cells in
series and operate a tape recorder or a radio? I usually have a contest in my class to see which student
can generate the largest voltage by inserting two pieces of metal into a lemon. No student has yet
generated a voltage higher than the voltage that I can generate. What electrodes would you use? Why
is it that we can generate a voltage sufficiently high to run a clock or a tape recorder, but we cannot
use the same cell(s) to start a car? If the car would start from this cell we could eliminate problems
and expenses due to cold weather starting.
OVERHEAD PROJECTION MODEL
CAUTION
Excessive heat will damage the clock mechanism.
If the clock mechanism is allowed to sit directly on the projector stage it (the plastic clock case) will
melt.
Mount the clock on a sheet of plexiglas; use it in the same manner as indicated in the previous
discussion.
Raise the clock above the stage of the overhead projector with either small blocks of wood, or rubber
stoppers
under each of the 4 corners of the plexiglas.
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If you are using both the cardboard mounted and the plexiglas mounted clock at the same time, they
must be connected in parallel. Connect both clocks to the same electrodes in the manner described
earlier.
REFERENCES
IDEA Bank Collation (Idea No. 618)
Paul Kelter, J CHEM ED., December 1997
Paul Kelter, Chem Ed 89
Special thanks to Paul Kelter for making some comments and
suggestions to me that resulted in the development of this activity.
Experiment No. 2
THE CHARACTERISTICS OF LIFE
This is an excellent experiment that is designed to show a teaching technique that crosses over ALL
subject areas.
Equipment
overhead projector
pair of long tweezers (125 cm)
glass petri dish (10 cm diameter)
medicine dropper
screw cap bottle (waste materials)
Procedure
i) Prepare the equipment before the class enters the room.
ii) Place a clean petri dish on the stage of a carefully leveled overhead projector.
iii) Put a drop of clean mercury in the center of the petri dish.
iv) Add enough distilled or deionized water to just cover the drop of mercury.
v) Project the petri dish on a screen or directly onto the wall.
vi) Focus the overhead projector on the mercury. The mercury drop will appear as a "black dot" on
the screen.
vii) If the mercury drop does not stay in the center of the petri dish place cover slips under the rim of
the petri dish to level the petri dish. It is not essential that the mercury drop be in the center of
the dish for the exercise to be successful, but it helps in following the procedure outlined below.
viii) Place a cardboard box, open at both ends, around the petri dish, so that the class can see the
"black dot" on the screen, but cannot see (directly) the petri dish and its contents on the stage of
the overhead projector
ix) The apparatus is now prepared and ready for use. If the apparatus is not going to be used
immediately, cover the open petri dish with a watch glass or with a second petri dish, in order to
prevent evaporation of water from the system, and at the same time prevent airborne particles
from falling into the water in the Petri dish.
This demonstration has been used in junior (grades 5 - 10) classes, as well as with senior classes and
in-service teachers, to introduce the Characteristics of Life. I do not tell the students the identity of
the black circle that they see on the screen. I ask them to describe what they see and to suggest
whether the "thing" that they see appears to be alive or not alive.
The students will suggest a number of conditions that must be met in order for the "black dot" to be
considered alive. After they indicate some of their suggestions add a dropper full of concentrated
13
nitric acid to the water, in the vicinity of the mercury drop. The nitric acid will act as an "irritant
(stimulus)" for the model "amoeba". During the demonstration add "food" (potassium dichromate,
K2Cr207, crystals), in close proximity to the mercury drop.
The class discussion will focus in on the meaning and the significance of life and life functions. If
enough "food" is added to the system, the students may observe "mitosis".
The box (shield) around the petri dish serves to "insulate" the students from the chemical system. I do
not go into the chemistry of this demonstration with my junior (or even advanced) students. They are
forced to think about the meaning of life and the functions that living species exhibit.
Be careful in disposing of the wastes. The mercury drop can be drawn into an empty eye dropper and
then returned to a "waste mercury container" for future cleaning and reuse. Keep the mercury wastes,
covered with water, in a plastic bottle.
TYPICAL CLASSROOM Activity, Questions and Answers
Turn on the overhead projector. The image that the students see the on the screen is of the petri dish
and the mercury drop.
QUESTION Please describe what you see on the screen
Answer
A series of concentric circles, a black dot, an opaque dot, a black circle.
QUESTION The large circle is the outline of a petri dish. We are interested in the black dot in the
center of the circle (petri dish). What can you say about the thing that produces the
black image?
Answer
It is opaque, but we cannot tell its color. It may be a disk, a sphere, a hemisphere, a
cone, or any object which has a circular cross section.
QUESTION Is the thing, black dot, in the petri dish, under the petri dish, above the petri dish, or is it
actually part of the petri dish (imbedded in the glass)?
Answer
We don't know; we do not have enough evidence to make a decision.
QUESTION What other observations can you make about the black dot?
Answer
It is in the center of the petri dish. This is only true if the petri dish iscompletely level.
The dot may be against the side of the petri dish. It is not moving. It is symmetrical in
shape.
QUESTION Does the black dot appear to be alive or not? We are going to vote, and everyone must
vote. The word, appear, is added in because many students have said that they cannot
be certain since they do not have sufficient evidence to make a definitive decision.
Answer
The vote is usually almost entirely in favor of NOT LIVING. In most groups there is
usually at least one student who will, in jest., suggest that the black dot appears to be
alive.
QUESTION The vote is almost entirely in favor of the Not Living option. What evidence do you
have for this suggestion? You must have had a reason for voting the way that you did.
Answer
Record all of the students' answers on the board.
The dot is not moving.
It is not changing shape.
It is too uniform.
The dot is not growing.
The dot is not breathing (respiring).
The dot is not eating.
The dot is not excreting waste products.
The dot is not responding to stimuli, heat, light and sound. Heat and light from the
projector; sound from the class.
14
The dot is not reproducing I walk over to the student who makes this comment, look
him/her in the eyes, take his/her hand in my hand, and say. Would you on the stage of
an overhead projector?
QUESTION You are so negative. You did not really say anything positive about why you think that
the dot is not alive; almost everything that you said included the word not. If the dot
did do all of the things that you said it was not doing, then would you agree with me
that the dot is alive, or at least appears to be alive?
Answer
Most of the students agree, but some of them simply say, "No, the dot cannot be alive".
QUESTION Sorry, but you cannot have it both ways. If you say that the dot appears to be not alive
because it does not do all of the things on the list, then if it does do all of the things on
the list, you must agree that it appears to be alive.
Answer
In general all of the students now agree with the teacher statement that the dot may
appear to be alive if it does all of the things on the list.
QUESTION Let's see how the black dot reacts to some other stimuli. Add two droppers full of
concentrated nitric acid to the petri dish, in the vicinity of the mercury drop. The
students see some movement, they see signs of effervescence, and a wave motion
(streaming) in the
petri dish. What appears to be happening?
Answer
The black dot is breathing or respiring.
QUESTION Well, at least it appears to be exchanging gases with its environment. This might be
seen as breathing or respiration. Let's try another stimulus. I'm giving some food to the
black dot. Using a long pair of tweezers, add a few crystals of potassium dichromate,
K2Cr207(s) close to the mercury drop. The black dot attracts and consumes the
crystals (black colored on the screen). The black dot moves, changes shapes, surrounds
and consumes the potassium dichromate crystals. Add additional small quantities of
potassium dichromate. A trail of "waste products" also appear.
Answer
The black dot does appear to be alive.
QUESTION What do you call the arm or hook-like things that the black dot uses to capture food
particles?
Answer
Pseudopodia.
QUESTION What species do you know of that have pseudopodia?
Answer
Amoeba.
QUESTION Yes this is a giant amoeba.
Answer
But it has not reproduced..
QUESTION Just as with other species amoeba reproduction is not always successful on each
attempt. Let's see what happens when we give it more food. Add more of the
potassium dichromate crystals close to the mercury dot. On most trials this will result
in the mercury droplet splitting into two or more fragments. The fragments tend to
recombine as the mercury droplets move about.. The splitting process does not always
take place. The mercury must be very clean in order for the splitting to incur readily.
The students are impressed that the black dot exhibits all of the properties that they had originally said
that the black dot did not exhibit. They tend to agree that the black dot is actually alive. They agree
that the black dot is a large amoeba.
I do not allow junior classes to see the contents of the petri dish directly. I allow them to leave class
thinking that the dot is alive; that it is an Amoeba. The next day, when they return to class I talk to
them about models and analogies. What we have discussed is the Characteristics of Living Things.
The students were introduced to the Characteristics of Life through a process that involved them in an
interactive process. They were not simply told that living things do specific things.
15
CAUTION
1 Collect all of the mercury and store it under water in a screw cap bottle.
2 The aqueous layer in the petri dish contains some nitric acid. Wash the petri dish carefully. The
contents of the dish (other than the mercury) can be flushed down the drain with a lot of water.
3 Collect the mercury in a beaker, cover it with distilled water, and pour the water from one beaker to
a second beaker. Be careful to pour over a plastic dishpan, NOT over an open drain. In this way
the mercury will not be inadvertently poured down the drain.
4 Repeat the washing with distilled water a large number of times.
5 It is not necessary to remove all the wash water. The clean mercury can be stored under water and
used again.
Experiment No. 3
FLOATING CANS
Prepare an aquarium full of water. Ask the audience if a new can of, say, regular Coca Cola, will float
or sink. Whether it floats or sinks depends on the way that the can is placed in the water. You can
make the can float by lowering the can carefully into the water so that the “air bubble” in the curved
portion at the bottom of the can, remains in place. The can will sink if the air bubble is allowed to
escape. You allow the air bubble to escape by tipping the can.
Ask the appropriate question(s) as you place a number of different soft drink cans in the aquarium. I
use regular, diet, and caffeine free soft drinks of various brands.
Are ALL DIET soft drinks less dense than their "regular" counterparts? Why do the cans float at
different levels? What would be the effect of changing the temperature of the water in the aquarium?
What would be the effect of changing the temperature of the drink cans? What would be the effect of
using a liquid other than water in the aquarium?
What is the mass of sugar in the regular soft drink? What is the mass of "NUTRASWEET" in the Diet
soft drinks?
How do DIET drinks get as sweet, or sweeter than the regular soft drinks.?
Why do beer cans float? Why do Pub Draft Beers such as Guiness, Murphy and others float upside
down, and all the other beers float right side up? Why does the Guiness can, which is larger than the
corresponding regular beer can, contain less beer than the regular beer can?
The Center of Gravity of the Guiness is raised because of the "empty" space in the bottom of the can.
If you cannot bring beer cans into your classroom, you might want to camouflage them with some
spray paint. Only the effect of different cans will then be part of the experiment.
Please note that US soft drinks work better than Canadian soft drinks. This is true because of the
aluminum content of the US cans. The mass of the empty US can is lower than that of the comparable
Canadian can.
Your students can design a number of experiments to answer a wide range of questions that they may
ask.
Experiment No. 4
HYDROGEN – CHLORINE EXPERIMENT
16
A cylinder of Chlorine gas would be helpful, but not completely necessary.
A cylinder of Hydrogen gas is necessary
One length of glass tubing (Pyrex) – 25 cm long, 2.5 cm diameter (Approximately)
2 corks
One small bottle of conc ammonia
Chlorine genrator (Potassium permanganet and Con HCl)
Before proceeding with this experiment I make a point of telling the class that hydrogen and chlorine,
in the presence of light, react explosively with each other. I take the time to outline the series of
reactions that are assumed to be part of the reaction mechanism for this reaction. This is a standard set
of equations that is listed in most college chemistry texts.
Cl2
+
h
2Clo
Clo
+
H2
HCl +
Ho
Ho
+
Clo
HCl +
Energy
NET REACTION H2
+
Cl2
+
h
2HCl +
Energy
Prepare a Pyrex tube approximately 30 cm long and 2.5 cm in diameter (the dimensions are not
critical); fire polish both ends of the tube. For purposes of extra safety enclose the tube in a length of
"Safety Netting". An alternative would be to wrap the tube with transparent adhesive tape. Close
the tube with "cork" stoppers. Make sure that the corks are wet so that they will not crack. Collect the
hydrogen and chlorine (chlorine first) by the downward displacement of water. The tube must be
completely full of water when starting the gas collection. Fill approximately one half of the tube with
each of the gases. Careful: oxygen "poisons" the reaction. Make certain that there are no air bubbles
in the tube.
I usually fill the tube with distilled water since I can be certain that the water is air free. Once I have
the chlorine collected, I turn out the room lights and fill the second half of the tube with hydrogen, in
the dark. This is significant because I have already told the audience that the reaction takes place
spontaneously when the reaction mixture is exposed to light.
Clamp the tube firmly, but do not use excessive force in tightening the clamp. Aim the corks very
carefully. Place an explosion shield between the class and the experimental set-up. Teacher chatter
can be used to build up the surprise element. Cover the tube with a dark cloth and turn on the lights.
Prepare to uncover the tube…… but first……
CAUTION
Warn the audience to cup their hands over their ears since they will hear a very loud noise. This
caution must be repeated any time there is the possibility of an explosion and a loud noise. Uncover
the tube, with a flourish.
The students are disappointed when nothing occurs at this point. I usually pretend to be very upset
with the failure of the experiment. The hydrogen - chlorine reaction is supposed to take place
spontaneously, but apparently something went wrong. I must have set something up incorrectly. I
make the statement that "I'll take a picture so that I won't make the same mistake again the next time I
try this reaction".
Take a picture with a flash bulb. I use the Electrochemical Flashbulb (Experiment 5) to set off this
reaction. This leads into an additional discussion of redox and electrochemical cells. It also allows me
17
to tie a number of topics together. While discussing one topic I can say something like "Remember
the explosion with ....".
Make VERY SURE that the corks are aimed in a SAFE direction. Note the use of plastic netting - just
in case something goes wrong. I have never had one of these tubes explode, but the safety procedures
are a worthwhile investment. Oxygen-free chlorine can be generated by the reaction of concentrated
hydrochloric acid on solid potassium permanganate.
IDEA Bank Collation (Idea No. 31)
Chemical Demonstrations - Bassam Shakhashiri, Volume 1, Page 121
An Alternative Procedure – What follows is a simpler and possibly easier to use set of procedures….
I saw Viktor Obendorfer do the demonstration this way……
Remove the plunger from the barrel of a 60 mL plastic syringe. Attach a plastic stopcock to the luer
lock end of the plastic syringe. Fill the syringe with distilled or deionized water. Collect, by the
downward displacement of water, 30 mL of chlorine in the syringe. With room lights out, fill the
remainder of the syringe with hydrogen. Place a cork or rubber stopper in the open end of the syringe
barrel.
Complete the experiment as indicated above.
See EXPERIMENT #49 for a simplified method to use for the preparation and collection of various
gases.
Experiment No. 5
ELECTROCHEMICAL FLASHBULB
Use the same electrodes as were used for the Electrochemical Clock. One electrode is a length (25 or
30 cm) of magnesium ribbon wound around a coffee stir stick and the other electrode is a piece of
copper foil. It is best to use a large piece of copper foil folded in a few layers.
i) Clean the contacts of the flashbulb with a piece of sandpaper.
ii) Grip the flash bulb in a clamp attached to a support stand.
iii) Grip a 150 mL beaker of 6 M HCl in a clamp - fasten it to the support stand 15 cm below the
flash bulb.
iv) Attach the copper lead, with a length of hook-up wire, to one contact of the flashbulb.
v) Place the copper electrode in the beaker of 6 M hydrochloric acid.
vi) Attach the magnesium electrode, with a length of hook-up wire to the second contact of the
flashbulb.
vii) When you are ready to flash the bulb, quickly dip the magnesium electrode into the
hydrochloric acid.
NOTES:
If the flashbulb does not ignite, try reversing the flashbulb contacts. Try cleaning the bulb contacts
again. I find, for a reason that I have not yet explained, that this demonstration does not work as
predicted, each time.
18
This experiment serves to show that the voltage generated by this cell is sufficient to cause the
flashbulb to ignite. Have the students try other combinations of electrodes and electrolytes.
I use this demonstration at the end of the same session that was started with the orange juice clock
described in Experiment Number 1. The ideas complement each other very well. Why could we use
Orange Juice in Experiment Number 1, but not in this experiment? I also use this flash bulb to
explode the hydrogen-chlorine mixture described in Experiment Number 4.
These are questions the audience will be able to answer right away. If they have any trouble, ask them
how long a battery lasts in a clock, and how long the same battery will last in a flash gun?
The bulb must be mounted very close to the explosion tube - no more than 1 cm away from the tube.
Why?
See the February 1988 issue of The Journal of Chemical Education for a slightly different version of
this activity. The authors suggest using a set of four lemons with copper and nail electrodes in series.
They suggest putting a capacitor in series with the four lemon cells in order to get the appropriate
current flow to flash the bulb.
I purchased a few low voltage, low current motors to try. Will they work with the orange juice clock?
Experiment No. 6
HYDROGEN ORGANS
The commercial model of a "Hydrogen Organ" costs more than $75.00. I don’t know if it is still
available. However, I really prefer to use a number of much cheaper and more satisfying variations.
Any plastic or metal container will work well.
CAUTION
Warn the students about the loud noises that will be produced. Have each of them cover their ears
with their hands. Tell them not to put their fingers in their ears, but to cup their hands over each of
their ears. In my classroom I do not proceed with the demonstration until everyone has his/her hands
safely over their ears. I do not allow students to sit in the front row for this part of the demonstration.
Do not allow a crowd of students to gather around the "organ" just in case an event that was not
predicted takes place.
a) Pringle's Potato Chip Containers ...
A Pringle's chip can (or any cylindrical container) makes the best hydrogen bomb (organ). In addition
it usually is relatively inexpensive and also contains a tasty filling (to start with). Cut a hole, 1 cm in
diameter, in the plastic cap and punch a small nail hole in the metal bottom of the can.
Fill the container with hydrogen gas. The gas can be obtained from a cylinder of compressed gas, or
you can generate the gas with a Kipp Generator. Keep your finger over the nail hole in the base of the
container during the filling procedure. You can tell when the container is full because there is a very
slight change in the sound made by the gas rushing into and out of the container. Keep the container
vertical at all times
Place the container (small nail hole up) on a clay triangle, ignite the gas coming out with a burning
splint and wait. Make certain that the container is not placed under a light fixture. Turn the room
lights off in order to increase the effect of the demonstration. Hold a piece of paper near the flame.
The ignition of the paper will show the audience that the flame is still burning. The flame will start to
get smaller, will disappear, there will be a hissing sound, and then the explosion occurs.
19
Pringle's containers are available in a number of sizes. I find that the 30 cm container is the best one
to use.
With a little bit of practice I have developed the knack of grabbing the can just as the gas is about to
explode. I grab the can as soon as I hear the hissing sound, This sound becomes audible just a
fraction of a second before the explosion occurs.
The results are interesting and lead to a number of questions that can be asked of the students, or if
properly primed, by the students themselves.
i) Why is the explosion delayed?
ii) How did I know when to grab the cylinder?
iii) What causes the sound?
iv) Which size of Pringle's can would produce the highest pitch?
v) Which size of Pringle's can would produce the loudest explosion?
vi) Which size of Pringle's can would explode soonest?
vii) Why was the clay triangle used?
viii) Will the reaction work the same way with burner gas?
Methane?
Propane?
Butane?
The series of questions asked by the teacher as well as by the students takes the explosions out of the
realm of pure entertainment and puts them into a situation which leads directly into class discussions.
The students may decide to design additional experiments to answer some of their own questions.
I saw Lee Marek do an interesting variation of this explosion on the David Letterman Show. Lee
secured the Pringle’s Can with a set of 4 lengths of wood dowel. When the explosion took place the
can went upwards, but the column of chips remained in the volume enclosed by the dowels. It was a
tasty treat.
b) 32 Ounce, "Pardon the Ounces" - Plastic Cheese Container
Cut a hole (approximately 1 cm in diameter) in the bottom of a large plastic cheese container. Punch a
nail hole in the top. Fill the container with hydrogen gas and place the container on a clay triangle.
Light and wait. An eight ounce container can also be used, but the demonstrator must work more
quickly when preparing the container for the reaction. Note that this container can only be used once.
c) 48 Ounce Juice Can....
Make triangular openings on the bottom of the can with a can opener. Remove the juice through one
of these holes. Make a small nail hole in the top surface of the juice can. Fill the "organ" with
hydrogen and place it on a clay triangle. Light the hole in the top and wait. This can makes a very
loud report when the gas explodes. Make certain that the students are seated a significant distance
from the juice can. The can becomes dented but can still be used a large number of times.
CAUTION
Warn the students about the loud noise that will be produced. Have each of them cover their ears with
their hands. Tell them not to put their fingers in their ears, but to cup their hands over each of their
ears. It is important that they do not push their fingers into their ears because when the explosion
occurs they may tend to join their fingers. This is definitely not as healthy a thing for them to do. In
my classroom I do not proceed with the demonstration until everyone has his/her hands safely over
their ears. I do not allow students to sit in the front row for this part of the demonstration.
20
Experiment No. 7
COMBUSTION OF HYDROGEN
Fill 2 test tubes with hydrogen gas. Keep each of the test tubes inverted (open end down) until the
time is ready for each tube to be used. Ignite one of the tubes of gas over a candle flame and use it to
ignite the next tube.
1) Hold the test tube mouth down over the candle flame
2) Immediately move away from the candle flame
3) Hold the 2nd test tube, mouth up, under the first test tube so that the two tubes are in a straight
line, but at an angle of 60o with floor.
The students will observe that the second tube is ignited. The pop in the first tube is very quiet, and in
the second tube is considerably louder. You may want to do this part of the experiment once or twice
more in order for the students to see the results clearly. Repeat the process, but this time hold the first
tube mouth up for a few seconds before igniting the gas. In this case the gas in the first tube pops
loudly, and the gas in the second tube does not ignite at all. I usually ignite the remaining gas in the
second tube over the candle flame so that the students will actually see that there is still a combustible
gas in the tube. The experiment provides a very visual demonstration of the combustion and the
density of hydrogen gas. There are a number of questions that you or the students can ask.
Collect a large test tube or cylinder (1000 mL or even 2000 mL) of hydrogen gas. Make sure that the
cylinder is completely FULL of the hydrogen gas. Turn room lights off, ignite the gas by holding the
cylinder (open end down) over a candle flame. Immediately invert the cylinder (with the burning gas)
and hold the cylinder upright as if you were holding a torch. The effect is interesting and useful.
When the room lights are turned back on you and the students will observe a trail of liquid (clear and
colorless) flowing down into the cylinder. What is the liquid? How can it be identified? Why did the
gas not explode?
It is possible to do a wide variety of experiments with hydrogen gas, but only if the gas is purchased in
large cylinders. The major expense is the cost of the valve. The rental charges and the actual cost of
the gas itself is minimal. The valve for a large cylinder of hydrogen gas costs approximately
$200.00. The rental charges are in the order of $8.00 to $10.00 per month. The cost of refilling the
large cylinder of gas, 220 cu ft, or 6000 L, is approximately $20.00. The costs might even be lower if
you are in a school which has a technical education facility. The technical teachers would already
have a contract with the gas suppliers. Check it out; you can do a lot of chemistry if a source of
compressed gases is "on tap".
Experiment No. 8
COMBUSTION of HYDROGEN and HYDROCARBONS in
CHLORINE
Fill a glass cylinder with chlorine gas. Lower a burning paraffin taper or a long candle into the
chlorine gas. Fill a second cylinder with chlorine. Lower a burning jet of hydrogen into the chlorine
gas. Perform both experiments in a fume hood.
CAUTION:
21
The hydrogen jet must only be lit using a test tube of burning hydrogen gas. The jet should NEVER
be ignited with an open flame. See the previous experiment (Combustion of Hydrogen) for the
experimental evidence that the procedure can be performed and discussed in class. If you are not
sure of yourself ... Do NOT do this experiment.
Experiment No. 9
EUDIOMETERS
Construct a Eudiometer tube from a 40 cm length of glass tubing, a length of metric tape, a rubber
stopper and a nail. Force a nail through a very small hole in a rubber stopper. If the rubber stopper is
solid, drill a small hole with an electric drill; use a nail or a needle as the drill bit.
Stopper the glass tubing, enclose it in a length of SAFETY NETTING (or wrap it with transparent
tape), fill the tube with water. Collect approximately 10 mL of oxygen gas and 10 mL of hydrogen
gas, by the downward displacement of water, in the tube.
Invert the tube into an 800 mL beaker of water. Mount the tube, about 5 cm above the bottom of the
beaker, in a utility clamp on a support stand. Tighten the clamp loosely. Do not force the clamp; the
tube should be free to rotate with very little force exerted. Allow a minute or two for mixing to occur.
The clamp holds the tube firmly but still allows for some movement when the explosion takes place.
Touch the metal nail with an activated Tesla coil. The only thing that can "go wrong" is that the
rubber stopper will be blown out of the Eudiometer. This is a very good SAFETY valve.
Compare the volume and identity of the residual gas after the explosion with the volume and identity
of the residual gas that was predicted by the class. Repeat the experiment using 10 mL of hydrogen
gas and 5 mL of chlorine gas. The results are again quantitative. Chlorine can be generated by the
reaction of concentrated hydrochloric acid on solid potassium permanganate. See experiment number
4 for a simple and inexpensive means of producing and collecting chlorine gas. All work with
chlorine should be done in a fume hood. Use the results to predict the formulas of water and of
hydrogen chloride.
Experiment No. 10
COMBUSTION of METHANOL
Use an eye dropper to place a few mL of methanol on a watch glass. Dim the room lights and ignite
the methanol with burning splint.
Pour 20 mL of methanol into a large empty plasric water bottle. Close the bottle with a rubber
stopper. After a few minutes open the bottle, observe the sound ( from the excaping vapor) and then
close the bottle again. I have found that it is best to wait at least 10 min before trying to ignite the
methanol vapor.
CAUTION
Warn the students about the loud noise that may be produced. Have each of them cover their ears with
their hands. Tell them not to put their fingers in their ears, but to cup their hands over each of their
ears. In my classroom I do not proceed with the demonstration until everyone has his/her hands safely
over their ears. I do not allow students to sit in the front row for this part of the demonstration.
22
CAUTION
There have been reports in the literature that the plastic bottles suffer fatigue, after repeated useage. It
is possible for the plastic bottle to explode or splinter. This experiment must be done behind an
explosion shield, or, for the safety of demonstrator and audience, between two explosion shields.
Light a splint, uncover the bottle and carefully throw the splint into the bottle. After the reaction is
complete close the bottle. How and when you close the bottle will have an effect on the next part of
this demonstration.
The students can now discuss the difference between the combustion in the bottle and in the watch
glass.
What will happen if the bottle is uncovered again, and another burning splint is thrown into the bottle?
What will happen if the bottle is uncovered again, more methanol is added, and another burning splint
is thrown into the bottle?
Would the effects be different if ethanol, isopropyl alcohol, or another alcohol, had been used in place
of the methanol?
Experiment No. 11
COMBUSTION of MAGNESIUM
What conditions are necessary for combustion to take place? Most students believe that elemental
oxygen must be present for combustion to occur. This series of demonstrations can be used to
distinguish between oxygen and an oxidizing agent.
Students know that candles do not burn in an atmosphere of carbon dioxide. To emphasize this point
place a few candles in an aquarium or large beaker. Put a few chunks of dry ice in the container and
try to light the candles. Try a number of variations such as placing a candle in a beaker, in the
aquarium. Light the candle and watch what happens as the dry ice sublimes and enters the beaker.
The students can be “convinced” that combustion will not occur in the presence of carbon dioxide.
Pour a beaker of carbon dioxide into a beaker containing a burning candle.
CAUTION: Wear gloves when handling dry ice. Cut a small depression (2 cm in diameter, 1 cm
deep) in a rectangular (20 cm x 20 cm x 4 cm) piece of dry ice. Place a mound of magnesium turnings
in the depression. Prepare a second piece of dry ice with a similar depression cut into the block.
CAUTION: The demonstrator as well as the observers should wear safety or glass blowing glasses
whenever experiments with burning magnesium are being performed. Before igniting the magnesium I
tell the students to look away. I will tell them when they can look forward again. For maximum effect
turn off the room lights. Ignite the magnesium with a Bunsen burner or propane torch flame.
Do NOT look directly into the burning magnesium flame.
Quickly invert the depression in the second block of dry ice over the burning magnesium. The
students can now look forward again. You may have to repeat this process one or more times in order
to get the reaction going.
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When the combustion is complete ask the students to predict what they will see when the blocks of dry
ice are separated. Use a knife or spatula to remove the residue from the depression. After the students
have made their predictions use the knife or spatula to cut open the residue that is found in the
depression. Observe and explain all of the observations. Observe and explain the relative sizes of the
depressions in dry ice at the beginning and at the end of experiment.
The students predict that the depressions will be much larger than they were at the start of the
experiment, and that the residue will be a grayish colored mixture (black carbon and white magnesium
carbonate). The results that they actually observe are puzzling to them. I leave them with the
question:
Why is the residue pure white on the outside, pure black on the inside? I particularly like this question
because I honestly do not know the answer myself.
REPEAT the Demonstration using blocks of “WATER” Ice.
It should work, but does it?????
Another Alternative
Pour water to a depth of 1 cm in a series of gas bottles. Fill separate gas bottles with each of carbon
dioxide, nitrogen and chlorine.
CAUTION: Do NOT look directly into the burning magnesium flame.
Lower lengths of burning magnesium ribbon into each of these gases. Empty jam jars make excellent,
and very inexpensive gas bottles.
Place a length of wide diameter (2 cm) glass tubing into a flask of boiling water. Ignite a length of
magnesium ribbon and lower it into the steam in the glass tubing. The glass tubing is used to protect
the flask. It is much less expensive to replace a length of glass tubing than it is to replace a flask.
NOTE: Dry ice can be purchased from a number of dairies or plumbing supply companies. Check
your local university, college or hospital for a source of dry ice, liquid nitrogen and liquid oxygen. In
my class I make dry ice by the rapid expansion of carbon dioxide. This is only one of the advantages
of stocking large cylinders of compressed gases in the laboratory.
Follow-up experiment…….Will other metals burn in gases other than oxygen? Try burning sodium in
each of the gases?
Experiment No. 12
AQUARIUM ANALOGY - Two Aquaria
NOTE: I do NOT use the word "Equilibrium" in any of my classes prior to performing this
demonstration exercise with the class.
Start with two (2) aquaria of equal size. Fill one aquarium with water (you might want to add food
coloring to make the water level more visible) and leave the second one completely empty. Ask for
two volunteers from the class. The volunteers are given the five (5) rules listed below:
i) The volunteers must pour at exactly the same time.
ii) The containers (tin cans or clear plastic cups) must be as full as possible when the transfers are
made.
iii) Water cannot be caught during the pouring.
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iv) The aquaria cannot be tipped.
v) The containers must be used as scoops, not shovels; the transfer must be done calmly.
As soon as the "volunteers" are instructed to "START" I interrupt them and ask the members of the
class to PREDICT what "The water levels will be in each of the two aquaria when the experiment is
completely finished". The students generally make the same prediction ... "The levels will be equal
in the two aquaria "half and half". Allow the experiment to proceed without any additional comments
from you. The students will probably start making a number of comments as soon as the experiment is
underway. The students start to change their models based on the observations that they are making.
They will generally say things such as, the levels are not changing, there is a steady state, some may
even introduce the word equilibrium. If they do not introduce the word, then I have to tell them the
term.
Ask the students how the levels might be changed? Can we arrive at other equilibrium compositions?
Vary the sizes of the containers.
Vary the number of "reactants and products" (number of pours).
Vary the temperature ????
Be very careful in your choice of words when giving the instructions for this exercise. Do not give the
idea away before the students have had a chance to experiment with materials and thoughts. Be very
careful with your choice of pouring devices. If possible use only clear plastic or metal cups, tins or
beakers.
SAFETY: Avoid the use of glass pouring containers.
Predict the effect of providing the two volunteers with transfer containers of different sizes (one about
2 L and the second about 50 mL). Repeat the experiment with the unequal sized containers. Most of
the students will predict that equilibrium cannot be established with containers of different sizes. Do
the experiment.
The demonstration can be made into a student experiment with pairs of students using beakers and
dropping tubes. The experiment can be made quantitative by measuring the amount of water
transferred each time. Plot the results on a graph of "volume of water transferred" vs "number of
pours"
Experiment No. 13
AQUARIUM ANALOGY
One Aquarium
This experiment is slightly different from the equilibrium analogy. In this experiment we again use
the services of two volunteers, but this time there is only one aquarium, the full one. The volunteers
are provided with containers of the same size. One of the volunteers is instructed to remove water
from the aquarium, and the second volunteer is instructed to obtain water from the tap and to pour it
into the aquarium. The other guidelines are the same:
i) The volunteers must pour at exactly the same time.
ii) The containers (tin cans or clear plastic cups) must be as full as possible when the transfers are
made.
iii) Water cannot be caught during the pouring.
iv) The aquaria cannot be tipped.
v) The containers must be used as scoops, not shovels; the transfer must be done calmly.
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Ask the class to predict the water level in the aquarium when the experiment is completed. This time
the class should be right. The same amount of water is being removed from, and added to the
aquarium each time. Have the volunteers perform a few transfers to verify the prediction and the
model.
The students may suggest that this is another equilibrium analogy, but it must be pointed out that
equilibrium refers to a closed system, while in this case the system is not closed. Water is being taken
out of the system, and new water is being put in. We have established a steady state situation, but not
an equilibrium. This experiment is analagous to many natural phenomena, such as maintenance of
body characteristics in spite of food intake, waste secretion, etc. This experiment is an analogy to the
condition that we refer to as homeostasis.
Experiment No. 14
ELECTRICAL CELLS
This experiment can be done either as a demonstration, or as a student performed class experiment.
As a demonstration I like to perform this experiment on the stage of an overhead projector. The use of
a transparent (for the overhead projector) volt meter adds an interesting series of observations and
discussion to the demonstration. The whole class can be included in the discussion, observations and
explanations.
Immerse a pair of clean graphite electrodes in a concentrated aqueous solution of copper(II) chloride
(acidified with a few drops of concentrated HCl). The electrodes must be perfectly clean when the
experiment is started. Clean the copper off the electrodes with sand paper and / or concentrated nitric
acid.
Connect a DC voltmeter (0 – 3 v full scale) and a DC power supply (at least 6 volts DC) across the
electrodes. I use a hobby train transformer to provide a variable DC voltage. Slowly raise the voltage
(DC) between the graphite electrodes from O to 2 V. If the needle on the voltmeter moves to the left,
immediately reverse the current flow through the power supply, or reverse the voltmeter connections.
Observe the voltage and the reaction pattern. At what voltage did a noticeable reaction start to take
place? Students can predict/identify the reaction products at each of the electrodes.
Allow the reaction to proceed for a few minutes. Ask the students to predict the voltage that will be
read on the meter if the power supply is disconnected
[(removed from the circuit]).
Disconnect the power supply, but leave the DC voltmeter in the circuit. You are now in the position of
teaching the difference between an electrolytic cell and an electrochemical cell as well as shifts in
equilibrium, direction of current flow and other electrochemical ideas. This demonstration can be
related to the Electrochemical (Orange Juice) Clock (Demonstration No. 1). I also use this
demonstration to teach the terms anode, cathode, oxidation and reduction.
It is interesting to note, that when the power supply is removed from the circuit the direction of current
flow through the cell is reversed, but the voltage appears to be acting in the same direction. This is an
interesting opportunity to analyse all of the reactions taking place, and at the same time to teach the
student how a voltmeter works.
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When the cell (electrolytic cell) is being charged the voltmeter is actually measuring the voltage of the
power supply, not of the cell. When the power supply is removed from the circuit the voltmeter than
measures the voltage produced by the electrochemical cell.
Experiment No. 15
ELECTROLYSIS of SODIUM SULFATE SOLUTION
Prepare a very concentrated (it need not be saturated) solution of sodium sulfate in water. Add a
generous portion of bromothymol blue solution to the aqueous sodium sulfate solution. If necessary
add either some sulfuric acid solution or some sodium hydroxide solution in order to keep the
electrolyte light green in color. Sodium sulfate solution should color the indicator green (pH = 7).
The addition of acid or base may be necessary to counteract local water and/or air conditions.
Any DC power supply will work for this experiment. I try to use relatively inexpensive equipment,
hence the electric train power supply that I use. I purchased the "hobby" store power supply for
approximately $50.00. The minimal cost of this type of power supply may allow the school to use the
money thus saved to buy other more expensive materials and consumable supplies.
The electrodes for this experiment must be platinum. Many of the commercially available platinum
electrodes look black. The black coating is a layer of finely divided platinum (platinum black)
deposited on the electrodes in order to increase the surface area of the platinum and thus increase the
current that can flow through the system.
For this experiment the glassware must be very clean. I keep the Hoffman apparatus filled with
distilled water until just before use. After the electrolysis has continued for sufficient time that
measurable quantities of gas are produced, stop the reaction. Be careful when discussing the
observations that you do not use terms that have not yet been defined in class.
I collect (and keep separate) the observations that are made in each arm of the electrolysis (Hoffman)
cell. Interpret the observations and on the blackboard write the balanced half-reactions for the
processes that took place at each of the electrodes. I write the observations and equations for the
LEFT part of the cell, and the RIGHT part of the cell as far apart on the front board as possible.
On the basis of the observations and the equations that have been written by the students, ask them to
predict the color that will be produced when the cell is inverted into the beaker that was originally
used for filling the cell. The students will look at the two equations, and because they have not taken
account of the different volumes of hydrogen and oxygen that are produced, they will predict that the
resultant solution will be acidic and the indicator will turn yellow. Based on what has been written on
the board this is the only prediction that can be made.
Pour the contents of the Hoffman apparatus back into the beaker. You must be very careful to get
every drop of electrolyte back into the beaker. The reaction is very sensitive and the loss of only a
drop of the electrolyte may have a very negative effect on the reaction results. The students are
amazed that the resultant solution is green. Use the results of this reaction to define terms such as
anode, cathode, oxidation and reduction. The idea that the number of electrons lost at the cathode and
gained at the anode are equal will "fall" out of the experiment.
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Graphite (carbon) electrodes cannot be used in this experiment because the oxygen produced is
adsorbed on the surface of the electrode (anode) and the net results will not show the quantitative 2:1
ratio of hydrogen to oxygen that is expected.
See the S17 Science catalog for a very inexpensive Hoffman Apparatus. It is a small cell that can be
used either for demonstrations or for class experiments.
The choice of electrolytes and acid-base indicators is very limited. The pH of the solution must be 7.0,
and the indicator must change through three colors, the middle one at pH 7.0.
Experiment No. 16
PARALLEL & SERIES CIRCUITS - ELECTRICAL
UNKNOWNS
Obtain a regular bathroom fixture (four, five or six sockets) from your neighborhood hardware store.
The fixtures are not overly expensive; they cost between $20 and $30. In a normal bathroom, when
one of the bulbs "burns" out, all of the other bulbs continue to glow normally. The bulbs are
connected in parallel. Rewire the fixture so that all of the sockets are no longer wired in parallel.
Make certain that all of the electrical joints are covered with insulators. The fixtures are cheap enough
so that you might have more than one of them in your classroom. I keep one fixture unmodified so
that students can see what a new one looks like.
Make sure that all of the bulbs are screwed in properly. Unscrew the bulbs one at a time and observe
the results. The students are amazed that the results are so different than what they expected.
There are a number of alternate experiments that can be prepared for the students to perform.
Prepare a series of circuit boards in which light bulbs, resistors, switches and voltage sources are wired
together in parallel and/or series. Cover the hookup leads with a sheet of cardboard so that the
students can only see the components, but not how they are joined together. The task for the students
is to draw a circuit diagram. My students have accepted this challenge and asked if they could
construct circuits for their classmates to unravel.
Take note of the smaller (miniature) socket boards that are also available at a very reasonable price.
Each of the miniature sockets is electrically isolated from all of the other sockets on the bar. The
sockets can be connected to satisfy any conditions that are established. The bars are very useful, and
safe, for teaching parallel and series circuitry. Use a 9 volt battery to power the sockets and number
46 bulbs (6.3 volt) in the sockets. The rewired bathroom fixtures and the small socket bars are
available from S17 Science.
An examination question of this type is an ideal way to test what you have taught and what your
students have learned. Give each student a different circuit to wire. Ask them to design circuits to
satisfy specific conditions that you have defined for them. I have used this type of exercise for both
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teaching and testing. The students have admitted to "enjoying" the test or examination. The
complexity of the experiments that can be designed is a function of the grade level and experience of
the students. The experiments can be used to introduce concepts involved in introductory circuitry or
to evaluate students' progress at any level of sophistication. The scope of the teaching and testing
potential of these units is limited only by the imagination and creativity of the teacher and the students.
SAFETY: You may also use various forms of 6 or 12 volt power supplies and the appropriate
electrical components. Do NOT use open 110 volt lines.
NOTES for USE of the REWIRED BATHROOM Fixture
The Bathroom Fixture is designed to be used as a demonstration, which can lead into a series of
experiments that the students themselves can perform with miniature socket bars.
CAUTION
Do NOT allow the students to open the fixture, both for educational as well as for SAFETY
considerations.
CONSTRUCTION of the Fixture
The fixture was rewired so that one bulb is in series with the 110 volt source. The other three bulbs
(Numbers 2, 3 and 4) are in parallel with each other, and in series with the first bulb.
Suggested Bulb Arrangements
1. Screw 4 bulbs (2 - 40 watt bulbs and 2 - 60 watt bulbs into the fixture.
2. Plug the fixture into the 110 volt source. One bulb is now glowing brightly, and the other three
bulbs are either glowing dimly, or not at all.
3. With a marker, for future reference, mark the sockets 1, 2, 3, and 4. Use the number 1 to
mark
the socket which held the bulb which was glowing brightly.
4. Arrange the bulbs as follows:
Sockets 1 and 3
60 watts
Sockets 2 and 4
40 watts
Suggested Exercises
1. All four bulbs are screwed in tightly.
Q Ask the class how many bulbs are "lit".
A One
Q What are some reasons why the other three bulbs are not lit?
A The bulbs are not screwed in firmly OR The bulbs are "burned" out
2. Try to tighten the bulbs. The students will see that all of the bulbs are screwed in properly.
3. Suggest that you will replace the "bad" bulbs. Unscrew one of the bulbs, then another,
the students will observe the changes that occur.
4. Screw in all 4 bulbs.
Unscrew bulbs 4 and 2
Unscrew bulbs 4 and 3
Unscrew bulbs 2 and 3
Unscrew bulbs 4 and 2
and
Screw them back in
Screw them back in
Screw them back in
Screw them back in
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Alternately screw and unscrew bulb 4
Repeat all of the preceding but use 4 identical bulbs.
Repeat all of the preceding with a variety of bulb sizes
Unplug the fixture, unscrew all but bulb number 1.
As you walk to the front of the class, plug the fixture into the flasher unit (which is already in a 110
volt outlet) so that the students do not see what you are doing.
Start a discussion and the students will be surprised when bulb number 1 starts flashing. It will take a
short time before the flashing starts, them it will repeat in a regular pattern.
Ask the students to suggest:
a) What is happening
b) Why it is happening
c) What must have been done to start the process
d) Show them the flasher unit and ask how it works
The students will have to develop a number of models to explain how and why things are happening.
The level of the models and discussion will depend on the grade level and sophistication of the class.
Experiment No. 17
FLASHING LIGHTS - EXERCISE IN MODEL BUILDING
Connect a flasher (blinker unit) into any electrical circuit. Plug the bathroom fixture into the blinker
unit. Do not tell the students what you have done. Ask them to explain the observed effect, and then,
the electrical circuitry. The demonstration is very easy, very inexpensive, and very instructive. The
exercise can also be a lot of fun.
The flashers cost about $4.00 each and can be used any number of times. Incidentally, I purchased
the flashers at a display of "Christmas Lights" because I was interested in finding out how the lights
worked. Do you know how the flasher works?
I never let my students take the flashers apart. There are many models that can be designed to make a
flasher that should work. All the models are correct. The students must be correct, if the model will
work. I did take apart one of the flashers that I bought and I found that it contained a(n) .... Well,
what do you think?
Did you really think that I would tell?
Experiment No. 18
EXPERIMENTS in ELECTRICAL CIRCUITRY
Students can perform experiments to investigate concepts in elementary electricity using simple, safe
and inexpensive equipment. The equipment and the experiments are designed to allow students to
design, build and study simple parallel and series electrical circuits.
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APPARATUS and SUPPLIES
Socket strips (3 – 3 socket strip). Sockets will accept a bayonet type flashlight bulb, No. 47.
Electrical leads with alligator clips on each end
9 volt dry cell
battery clip
The sockets on any one unit are isolated from each other. The experimenter is free to wire them in
series, in parallel, or in some combination of series and parallel. The complexity of the experiments
that can be designed is a function of the grade level and experience of the students. The experiments
can be used to introduce concepts involved in introductory circuitry or to evaluate students' progress at
any level of sophistication. The scope of the teaching and testing potential of these units is limited
only by the imagination and creativity of the teacher and the students.
Notes for use of the Miniature Socket Bars
Use #47 bulbs, since these are rated for 6.3 volt and a current sufficiently large that they will not blow
if a student shorts out one of the bulbs across the 9 volt battery. This allows students to experiment as
they are learning to use the bulbs, leads and batteries.
Hold a socket bar so that the vertical hangers are behind the socket bar and the horizontal contact (the
single contact) is pointing towards you.
With the socket bar in this position there are two contacts pointing vertically downwards on each
socket. The vertical contact on the left is the one to use. The one on the right is dead.
This contact was probably used as a ground when the socket bars were used for their designed
purpose.
The sockets are all insulated from each other. They can be wired in series or in parallel, at the
discretion of the user.
When using these socket bars with a very junior class I use the following series of experiments. Please
note that the terms I have chosen to use are non-technical, at the outset. Later on in their study of
electrical circuits I will use the appropriate technical terms.
Each student, or group of students, is provided with a socket bar, a set of wires, a battery clip, a battery
and a number of bulbs, as determined by the teacher.
Tell the students which contacts can be used. Do not have them waste time finding out that one of the
contacts is not live.
FIRST EXERCISE (Teaching Series Circuits)
The instructions for the first part of the first exercise are:
Mount two bulbs in the socket bar.
Use the wires, battery clip and battery to join up the two sockets so that the two bulbs glow.
If either of the bulbs is removed from its socket both bulbs go out.
Draw a picture of the way that you have joined up the two sockets.
The instructions for the second part of the first exercise are:
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Mount three bulbs in the socket bar.
Use the wires, battery clip and battery to join up the three sockets so that the three bulbs glow.
If any one of the bulbs is removed from its socket all three of the bulbs go out.
Draw a picture of the way that you have joined up the three sockets.
The instructions for the third part of the first exercise are:
Mount four bulbs in the socket bar.
Use the wires, battery clip and battery to join up the four sockets so that the four bulbs glow.
If any one of the bulbs is removed from its socket all four of the bulbs go out.
Draw a picture of the way that you have joined up the four sockets.
The instructions for the fourth part of the first exercise are:
Mount five bulbs in the socket bar.
Use the wires, battery clip and battery to join up the five sockets so that the five bulbs glow.
If any one of the bulbs is removed from its socket all five of the bulbs go out.
Draw a picture of the way that you have joined up the five sockets.
The instructions for the fifth part of the first exercise are:
Mount six bulbs in the socket bar.
Use the wires, battery clip and battery to join up the six sockets so that the six bulbs glow.
If any one of the bulbs is removed from its socket all six of the bulbs go out.
Draw a picture of the way that you have joined up the six sockets.
SECOND EXERCISE (Teaching Parallel Circuits)
The instructions for the first part of the second exercise are:
Mount two bulbs in the socket bar.
Use the wires, battery clip and battery to join up the two sockets so that the two bulbs glow.
If either of the bulbs is removed from its socket it goes out but the other continues to glow.
Draw a picture of the way that you have joined up the two sockets.
The instructions for the second part of the second exercise are:
Mount three bulbs in the socket bar.
Use the wires, battery clip and battery to join up the three sockets so that the three bulbs glow.
If any one of the bulbs is removed from its socket it goes out but the other two continue to glow.
Draw a picture of the way that you have joined up the three sockets.
The instructions for the third part of the second exercise are:
Mount four bulbs in the socket bar.
Use the wires, battery clip and battery to join up the four sockets so that the four bulbs glow.
If any one of the bulbs is removed from its socket it goes out but the other three continue to glow.
Draw a picture of the way that you have joined up the four sockets.
The instructions for the fourth part of the second exercise are:
Mount five bulbs in the socket bar.
Use the wires, battery clip and battery to join up the five sockets so that the five bulbs glow.
If any one of the bulbs is removed from its socket it goes out but the other four continue to glow.
Draw a picture of the way that you have joined up the five sockets.
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The instructions for the fifth part of the second exercise are:
Mount six bulbs in the socket bar.
Use the wires, battery clip and battery to join up the six sockets so that the six bulbs glow.
If any one of the bulbs is removed from its socket it goes out but the other six continue to glow.
Draw a picture of the way that you have joined up the six sockets.
THIRD EXERCISE (Teaching Parallel and Series Circuits)
The instructions for the third exercise are:
Mount four bulbs in the socket bar.
Use the wires, battery clip and battery to join up the four sockets so that the four bulbs glow.
If one of the remaining bulbs is removed from its socket it goes out but the other bulb continues to
glow.
Draw a picture of the way that you have joined up the four sockets.
FOURTH EXERCISE ((The Effect of Changing the Voltage)
Repeat any of the previous exercises using either a higher or a lower voltage battery.
TESTING and EVALUATION
Use a marker to number the sockets on each bar.
Provide each of the students with a box, containing all of the equipment, except the battery.
Give each student a customized question sheet with his or her name on it.
The customized question tells the student what results you want him or her to achieve.
You keep the battery in your pocket and test the students' circuits when they call you over.
When the students have completed their work tell them to turn in their work, and their question sheet
in the box that you provided. You can now check the circuits that they constructed and arrange
remedial work for any of the students who appear to need extra help.
SOME SAMPLE TEST QUESTIONS
Please note that the questions can be of varying difficulty, from grade to grade, or even within the
class. Do not give very difficult questions to students who are still having difficulty with the concepts.
Conversely, do not give easy questions to those students who have mastered the necessary concepts.
You have the option of using words such as circuit, circuit diagram, parallel and series, in your
questions. You also have the option of not using these technical terms.
1. Wire the socket bar so that bulbs 1, 2 and 3 are in series with each other and in parallel with 3 & 4.
2. Wire the socket bar so that bulbs one, two, three and four are in series with each other.
3. Wire the socket bar so that bulbs one, two, three and four are in parallel with each other.
4. Wire the socket bar so that bulbs one, two, four and five are in parallel with each other.
5. Wire the socket bar so that bulbs 1, 2 & 3 continue to glow when bulb 4 is removed from the
socket.
6. Wire the socket bar so that bulbs 1 & 2 continue to glow, but bulbs 3 & 4 go out when bulb 5 is
removed. from the socket.
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7. Construct the circuit shown in the accompanying circuit diagram.
There is no end to the number of different questions that you can write. Some of the different
questions may even be identical. Just change the numbers that are referred to in the question.
Experiment No. 19
ROLLING SPHERES DOWN AN INCLINED PLANE
The special equipment required for this experiment is simple and can be improvised. Use as strong a
magnet as is available. The size of the metal spheres can be adjusted to complement the strength of
the magnet. Large steel spheres are available from a number of sources, both commercial and
otherwise. The inclined plane has a nail in place in order to give all the spheres the same acceleration
and velocity.
Roll a non-metallic (or at least non-magnetic) sphere down the inclined plane and observe where it
goes. I use a porcelain or ivory cue ball. Repeat the experiment with a number of spheres of different
diameters. Observe the path taken by each of the spheres from the time that they leave the inclined
plane until they enter one of ice cube tray slots. Ask your students to predict the paths of each of the
different sized spheres that are rolled down the inclined plane.
Do not start out by describing the apparatus to the students. Allow them to make their own
observations and inferences. I use a transparent Plexiglas sheet so that the students can see the magnet
under the sheet, but I do not tell them that the object under the Plexiglas sheet is a magnet. The
magnet is taped between two pieces of wood (2 x 4, please excuse the use of these units) so that the
large spheres, while rolling down the inclined plane, will not move the magnet . The intent of the
experiment is to teach the use of a Mass Spectrometer. I expect that the students already understand
some principles of magnetism. The model can be extended to compare atoms of the same element
(isotopes) as well as atoms of different elements. In addition to the Mass Spectrometer, I use this
exercise to introduce and reinforce the "Scientific Method". In my classes I do not teach the Scientific
Method, rather, I use the Scientific Method in my teaching examples. It is also possible to use the
experiment to build a model of how magnets effect the path of moving metallic spheres. How would
the paths of metallic cylinders be effected by the magnetic field.
The Plexiglas sheet is mounted on four pieces of 2” x 4”. The launching ramp is attached to the
Plexiglas sheet with a length of 2-sided tape.
The position of the nail can be altered if necessary, in order to allow spheres to roll by the magnet
faster or slower.
One way of using the equipment is to gather the students around the apparatus and carry out an
exercise such as the one which is described in the following narrative.
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TEACHER Class, for this experiment I would like you to observe quietly. Please do not discuss
any of your observations or thoughts with anyone else. Please respond only to my questions and
comments.
TEACHER Bounce a non-magnetic sphere on the table so that the students can “see” it does not
appear to be metallic.
TEACHER Without any comment,.hold the sphere against the nail, and allow it to roll down the
ramp and into one of the ice cube trays. You will do the same thing with the other spheres as the
experiment proceeds.
TEACHER Select the largest of the steel spheres. Tell the students that it is steel, and have them
compare the masses of the first (non-metallic) sphere and the steel sphere. The steel sphere will have
a mass of approximately 8 times that of the non-metallic sphere. Bouncing the sphere before using it
in the experiment will remove any temporary magnetism that may have developed in the sphere during
storage in a box with magnets.
TEACHER Class, I am going to roll this sphere down the ramp in the same way as the first one was
allowed to roll. Please predict where you think the sphere will end up. Do not ask for any
explanations.
STUDENTS Students will predict that the sphere will take one of three different paths….the same
path as that taken by the first sphere, or to the left or to the right of the first sphere.
TEACHER Select the next smaller steel sphere, bounce it on the table top, allow students to
compare the masses of the two steel spheres, and the first non-metallic sphere. It is readily apparent
that this smaller steel sphere is lighter than the first (larger) steel sphere, but heavier than the nonmetallic sphere. Ask the students to predict where this sphere will end up when it is rolled down the
ramp. There are five (5) possibilities.
STUDENTS Most of the students will predict that this sphere will end up between the non-metallic
sphere, and the larger steel sphere. This is really the ONLY logical prediction that they can make, at
this point.
TEACHER How do you know? Note that at this point the students do not have very much
evidence. They do not know, for sure, that the object beneath the Plexiglas sheet is a magnet.
STUDENTS The sphere is between the first two in mass, therefore it will end up between them.
TEACHER Roll the sphere down the ramp. Allow the students to observe. Do not ask any
questions yet, and do not allow the students to ask any questions either.
TEACHER Select the next smaller sphere; ask the students to predict it’s path. Do not ask for
explanations. Repeat this process with a number of spheres. Some of the students will, after a few
trials suspect that the object beneath the Plexiglas must be a magnet.
TEACHER After a number of incorrect predictions, roll a very small sphere down the ramp. The
sphere will “stick” to the magnet
35
All of the spheres have the same velocity when they pass through the magnetic field. The position of
the nail can be compared to the charges on the ions in a mass spectrometer. The position of the nail
can be altered to change the particle velocity and simulate different electrical fields.
In this exercise we used, rather than discussed the Scientific Method. It is now possible to compare
the model to the MASS SPECTROMETER, and/or to the processes of science.
Experiment No. 20
HOW AIRPLANES STAY ALOFT
Tie closed one end of a long plastic tube. Ask one student to blow up the tube with his/her breath.
Have one student hold the closed end of the tube and extend the tube to its full length. Count the
number of puffs that were required to inflate the tube. Most students will require 20 to 30 breaths to
fill the bag.
Have one student hold the closed end of the tube and extend the tube to its full length. Hold the open
end of the tube about 6” (15 cm) from your mouth. Take a deep breath and gently blow your breath
into the tube. It will become inflated with only one or two breaths. Challenge the students to explain
the difference.
Place two books of the same thickness about 3” apart on a desk top. Place a sheet of paper on the
books. Challenge the students in your class to blow the sheet of paper off the books. The only
condition that you set is that the students must blow their breath horizontally towards the edge of the
paper. They are amazed that the paper not only does not blow off the books, but appears to become
more firmly attracted to the books and to the desk top.
It looks like Bernoulli forces are really here to stay.
Experiment No. 21
LEVITATION and the GAS BAG –or—
"HOW TO MOVE a REFRIGERATOR"
Place two plastic tubes (each tied at one end) on a table surface. Invert a second table or place a sheet
of wood over the plastic tubes. Ask a "volunteer" to stand on the inverted table. Invite two more
volunteers, to blow their breath into the plastic tubes. Have the volunteers start at the same time, on a
given signal. The students are amazed that they can lift a table and a person on the table with only
their breath.
Assign a simple problem. Given a tire gauge and a standard piece of office equipment (a short ruler)
design an experiment to weigh an automobile. Using this equipment the students should be able to
"weigh" an automobile within 10% of the value noted in the users' manual. This experiment provides
a good way of merging practice and theory. The concept of pressure as a force per unit area is
reinforced.
Experiment No. 22
36
SHAPES of CARBON COMPOUNDS
Trace an equilateral triangle (15 cm to the side) onto a piece of cardboard or acetate. Cut out the
equilateral triangle. Bisect each of the sides of the triangle. Join the mid points of pairs of sides.
Score the internal lines. Fold and tape the figure to form a tetrahedron.
Trace the cubic shape onto a piece of cardboard or acetate. Cut out the external (large) pattern. Score
the internal lines. Fold and tape the figure to form a cube. The diagonal of the cube is 15 cm.
Prepare a tetrahedral "Ball and Spring" model of the carbon atom. Place the Ball and Spring model
into an open cardboard tetrahedron. Notice how the two fit together.
Pairs of the tetrahedral models can be used to study the shapes of molecules with formulas such as,
C2H6, C2H4, and C2H2. Use transparent (acetate) tetrahedra to make the effect even more evident.
Place a cardboard tetrahedron into an open cardboard cube. Notice that the tetrahedron is formed by
joining the opposite corners of a cube. Hence the relationship between tetrahedral and cubic
structures.
Experiment No. 23
MOLECULAR SHAPES and BONDING (VSEPR Theory)
Spherical rubber balloons labeled shared pair and UNSHARED PAIR make excellent teaching aids
when discussing molecular shapes. The shapes of all the first row fluorides and hydrides can easily be
demonstrated using Valence Shell Electron Pair Repulsion (VSEPR) theory. There is no need to go
into complex hybrid orbital theory at the high school level, or, I am told, at the introductory college
level. The students must be told, or shown, that an UNSHARED PAIR will take more space than a
shared pair. The balloons will do the rest of the work.
Select one volunteer to act as a kernel (nucleus) and a second volunteer to act as an UNSHARED
PAIR (of electrons). The "nucleus" holds one of the hands of the UNSHARED PAIR. The
UNSHARED PAIR is instructed to wander about as freely as he/she can.
Select 2 volunteers to act as kernels (nuclei) and a 3rd volunteer to act as a shared pair (electrons).
The "nuclei" each hold one of the hands of the shared pair. The shared pair is instructed to wander
about as freely as he/she can. It is easy to recognize the difference in size of the orbitals of the shared
pair of electrons and the UNSHARED PAIR of electrons. The UNSHARED PAIR has more freedom
of movement and therefore a larger orbital.
A simple experiment to show the difference in polarity between molecules can be done with two
burets and charged ebonite and glass (or plastic) rods. Run water out of a buret. Hold a charged rod
near the water stream. Repeat the experiment with a stream of toluene, or some other non-polar liquid.
The comparison, as long as the streams are running at the same rate, is effective. Other liquids with
differing polarities can be used to increase the data base available.
Experiment No. 24
37
THERMOMETERS and THEIR USE
I use ungraduated thermometers to introduce the ideas that are involved in establishing particular
temperature scales. On day 1 allow the students to measure the temperature of a number of liquids and
other things in the laboratory, with a real thermometer. Among the things whose temperatures are
measured are a beaker of boiling water and a beaker of ice-water.
On day 2 I have the students measure the temperature of a series of unknowns, with an ungraduated
thermometer. The only common materials present on day 2, that were also present on day 1 are the ice
water and the boiling water. The students are able to make the connections that are necessary.
The students have devised a number of creative methods of relating the temperature of the unknown to
the temperature scale that they have developed, using two fixed points as their reference points. They
learn something about calibration, graphing and temperature scales themselves in the process.
This can be done with students at all grade levels. The challenge of determining the temperature of a
liquid without the use of a “real” thermometer has given many of my students an opportunity to
express true creativity. Students have devised their own temperature scales with valid reference
points. Their scales are every bit as realistic as the ones that are in general use. I have used this
exercise with students from grades 6 through to students in various MSc programs.
Experiment No. 25
UNKNOWN SAMPLES
Distribute a sample of Unknown No. 1 to all members of the class and ask them to design experiments
to identify the unknown. I tell the class that the unknown is an element. I generally use this
technique to introduce or to review periodic table considerations.
I have found that, if I sit in front of the class and act as the source of all observational data, the class
can identify the unknown element within 15 or 20 min. Unknown No. 1 is the element silicon, Si. An
alternative procedure is to give the students a specific period of time during which they can perform
the various experiments that they have designed.
The students must tell me what experiments they are going to do, and exactly how they are going to do
the experiments. I give them the observations that they will see.
Using the periodic table as a reference the students can either identify the Si, or relate it to other
elements.
The silicon available from FLINN Scientific, Inc, Box 219, Batavia, Illinois, 60510.
Experiment No. 26
SPECTRAL EMISSION
The relatively sophisticated plastic analyzers, with wavelength calibrations, that we used are available
for approximately $10.00 per unit. The analyzers (spectroscopes) consist, essentially, of a slit, a
screen and a diffraction grating. The equipment is inexpensive enough that a class set is practical.
The experimental results are useful in teaching an introductory unit in spectra and atomic structure.
38
Examine the light from a fluorescent light source, the sun and a white light source with a diffraction
grating spectroscope. Compare the spectra with those produced by a spectral discharge tube. Use
spectral discharge tubes that contain samples of mercury vapor, hydrogen gas, helium or neon gas.
Students will observe that the spectra of the light from the sun, from a fluorescent light and from a
white light lamp are the same in all but one respect. The fluorescent light (older versions that did
contain mercury vapor) includes extra lines in three specific areas. These lines are the same as those
present in the spectrum of mercury vapor.
This phenomenon can be expanded to a large number of gases and vapors that can be examined with
the simple spectroscopes. I have encouraged my students to do some qualitative analysis using these
diffraction grating spectroscopes. Students can do flame tests using these spectroscopes and measure
the wavelengths of specific spectral lines in an “unknown”
Experiment No. 27
THE OSCILLATING CLOCK REACTION
There are many clock reactions reported in the chemical literature. I use them to initiate student
interest; I do not require that the students study the chemistry of the reactions; it is too complex for
high school students. They can, however, design experiments to vary the time intervals between the
oscillations, and to change the "life" of the system.
This reaction is only one example of a number of different time dependent "clock" reactions. It is
taken from Vol 2 of CHEMICAL DEMONSTRATIONS (Shakhashiri).
The solutions for this reaction are:
1) 4.0 M hydrogen peroxide (410 mL of 30% hydrogen peroxide diluted to 1 L.)
2) 0.2 M potassium iodate, 0.077 M sulfuric acid (43 g of potassium iodate and 4.3 mL of
concentrated sulfuric acid, diluted to 1 L).
3) 0.15 M malonic acid, 0.02 M manganese(II) sulfate (16 g of malonic acid and 3.4 g of
manganese(II) sulfate diluted to 500 mL. Mix 0.3 g of soluble starch in 50 mL of boiling
water; add the starch suspension to the 500 mL of solution, and dilute with water to 1 L.)
Mix 500 mL of solution 1 with 500 mL of solution 2 in a 2 L beaker. Add 500 mL of solution 3 to the
beaker containing the first two solutions. The effect can be improved by using a magnetic stirrer.
Experiment with each of the reagents. The concentrations of the reagents will determine the rate of
oscillation as well as the lifetime of the clock. The reaction will last for approximately 20 min. Do
not start the "clock" until the class is starting to settle down. What effects are observed by varying the
temperature (increasing or decreasing)?
Other interesting reactions of this type are The Iodine Clock Reaction which is found in most
standard text books, and The Old Nassau Reaction This latter reaction has been performed by, and
has been made popular by the late Dr. Hubert Alyea. It can be found in Tested Demonstrations in
Chemistry (Chemical Education Publishing Company), a compilation of many demonstrations from
the column in the Journal of Chemical Education.
The Oscillating Clock Reaction kit is available from Flinn Scientific. PO Box 219, Batavia, IL,
60510, and in Canada, from S17 Science Supplies and Services Co. Ltd.
Experiment No. 28
39
BLUE BOTTLE EXPERIMENT
The BLUE BOTTLE EXPERIMENT is outlined in considerable detail by the late J.Arthur
Campbell in, "Why Do Chemical Reactions Occur" (Prentice-Hall 1965). Variations of this
reaction have been published in a variety of works since 1965. The recipes that are given in this
outline may require some changes. Try the experiment in your laboratory before using it in class.
Place a 500 mL clear plastic bottle containing 200 mL of a clear, colorless solution, on the front of the
demonstration table. Pick up the bottle and casually shake (rotary) it to produce a vortex type effect.
The contents of the flask turn blue. The bottle is set back down on the table, and in a few moments
the contents return to the clear, colorless state in which they were originally observed. This process
can be repeated a great number of times during the next few hours.
Ask the students to speculate on the process that is taking place. Tell them that the solution contains a
caustic solution and that they must be careful in handling the system. On many occasions I have
prepared a number of samples of the solution and before the start of the class I left a sample of the
solution, in a closed bottle on each student's desk. The members of the class are hesitant to jostle the
bottles until one member of the class starts to examine his / her bottle more carefully. The others then
join in.
An alternative is to have a second flask which behaves a little bit differently from the first. The
second flask contains a clear, green liquid which turns red on gentle agitation then yellow on more
active agitation. On standing, the liquid changes back to red then green. The "mixed" solutions must
be prepared immediately before use. The indicators deteriorate on standing in contact with the active
ingredients. The indigo carmine deteriorates much more rapidly than the methylene blue.
The flask with the methylene blue can be prepared a few hours before the intended use. You may find
that the colourless solution tends to turn a cloudy yellow on standing. The flask with the indigo
carmine should be prepared approximately 20 minutes before the intended use to allow time for the for
all of the solide indicator to dissolve.
Stock solutions
1) Aqueous sodium (or potassium) hydroxide
2) Aqueous dextrose (glucose)
40 g per L
24 g per L
Bottle 1 (500 mL) - Colorless/Blue
100 mL sodium hydroxide solution
100 mL dextrose solution
A few crystals of methylene blue indicator
Bottle 2 (500 mL) - Green/Red/Yellow
100 mL sodium hydroxide solution
100 mL dextrose solution
A few crystals of indigo carmine indicator
You may have to prepare the bottles a few times before you will be completely happy with the results.
I find that I have to add much more of the indigo carmine than the methylene blue. Try using as small
a sample of methylene blue as possible. The rate at which the colours change varies as time goes on.
In each case the bottles must be, at most, half full of the combined solutions. Additional amounts of
the indicators may have to be added in order to get the reaction started. It takes a few minutes for the
40
second bottle (indigo carmine) to start working. Do NOT shake it repeatedly until you are ready to
use the bottle in class; this system does not last for as many repetitions as the methylene blue system.
If you do prepare samples of the solutions for the students to manipulate please be certain that their
containers are of the screw top type, and that the tops are liquid tight.
What would be the effect of:
increasing the concentration of the sodium hydroxide solution?
increasing the concentration of the dextrose solution?
decreasing the concentration of the sodium hydroxide solution?
decreasing the concentration of the dextrose solution?
increasing the temperature of the solution?
decreasing the temperature of the solution?
The students can design a whole series of experiments to study the effects of temperature and
concentration on the rate of a chemical reaction. They may have some other ideas that can be
investigated. There are a number of other ideas for investigation suggested by Dr. J. Arthur Campbell
in Why Do Chemical Reactions Occur?
The Methylene Blue and the Indigo Carmine Reaction kits are available from Flinn Scientific.
PO Box 219, Batavia, IL, 60510, and in Canada, from S17 Science Supplies and Services Co. Ltd.
Experiment No. 29
CONDUCTIVITY OF ACIDS AND BASES
Use a commercial or home made apparatus to test the electrical conductivity of water and then
solutions of each of the following:
i) glacial acetic acid
ii) concentrated ammonia
iii) dilute acetic acid
iv) dilute ammonia
v) hydrochloric acid solution (approximately 1 M).
Use a squeeze bottle to add distilled water to the solutions of concentrated ammonia and glacial acetic
acid. The change in conductivity of the solutions is striking.
Instruct the students to assign a number from 1 to 10 to describe the conductivity of each of the 4
solutions.
The conductivity of the glacial acetic acid and the concentrated ammonia solutions were each
measured to be zero (0). The conductivity of the hydrochloric acid solution was 10.
Predict the conductivity of a solution made by mixing small samples of concentrated ammonia and
glacial acetic acid solutions.
CAUTION:
The reaction of glacial acetic acid with concentrated ammonia is highly exothermic. Make certain that
everyone is standing well back when this mixture is prepared.
41
Add ONLY a few drops of concentrated ammonia to a beaker of glacial acetic acid. The results are
startling.
Experiment No. 30
PHOTOCHEMICAL REDUCTION OF THIONINE
A REVERSIBLE REACTION
Prepare a 0.001 M aqueous solution of thionine (0.23 g of thionine per liter of solution). Prepare only
as much of the thionine solution as is required for a few repetitions of the experiment. Thionine is
quite expensive. Mix 10 mL of the thionine solution with 10 mL of 3.0 M sulfuric acid solution. Add
sufficient distilled water to make 500 mL of solution. Add 2.0g of hydrated iron(II) sulfate to the
solution.
Shine a very bright light into the solution. The solution turns colorless, then returns to its original
color in a few seconds. The process can be repeated a great number of times. The same sample of
solution can be used a number of times over a three or four day period. The bleaching and restoration
times should be checked periodically. Is the light or the heat the cause of the reaction? Design an
experiment to determine which is the primary effect.
Place a 600 mL beaker, filled to a depth of 4 cm with the solution, on the stage of an overhead
projector. Place a piece of cardboard under half (semi-circle) of the beaker. Turn on the overhead
projector and observe the effect for a few seconds. Pull the cardboard out from under the beaker and
observe the color on the screen; note how the color changes quickly.
This demonstration has been adapted from a paper by Lawrence J. Herdt which appeared in The
Journal of Chemical Education a number of years ago, (26 s25, 1949).
The Thionine Reduction kit is available from Flinn Scientific. PO Box 219, Batavia, IL, 60510, and in
Canada, from S17 Supplies and Services Co. Ltd.
Experiment No. 31
Equilibrium Constant
1)
2)
3)
4)
5)
6)
7)
8)
NO2 / N2O4
Determine the mass of an empty 140 mL (Experiment No. 50).
Determine the mass of the syringe full of a gas.
Calculate the number of moles of gas that can be contained in this syringe.
Calculate the mass of NO2 required to fill the syringe.
Calculate the mass of N4O4 required to fill the syringe.
Fill the syringe with a sample of the gas mixture (NO2 and N4O4).
Determine the mass of the syringe full.
Calculate the actual mass of the gas mixture in the syringe.
“x moles”
Using the data that has been gathered it is now possible to calculate the equilibrium constant for the
NO2 and N4O4 mixture.
The total number of moles of NO2 and N4O4 in the syringe is x moles. This is a known number.
If the number of moles of NO2 is represented by z moles
Then the number of moles of N4O4 is represented by (x – z) moles
Mass of NO2 in the syringe is 46(z) grams
42
Mass of N4O4 in the syringe is 92(x - z) grams
46(x) +
92(x – z)
=
The mass of gas in the syringe.
Solve the equation for “z”, the number of moles of NO2
Calculate the value of (x – z) and now the equilibrium constant can be determined.
The results in this experiment are not very accurate, but they are within ranges that look
understandable.
Experiment No. 32
SHELL GAME
Before the students are in class place one spoonful of sodium polyacrylate in one of five paper cups.
All of the other cups are empty. The active ingredient in many of the "dry" diapers is sodium
polyacrylate. Sodium polyacrylate will absorb almost 900 times its own mass of water. There are
many questions that will be raised in class as a result of this experiment. This is a good example of
how science, society and technology can be related in the classroom.
I usually perform this demonstration in the form of the “Shell Game” that was popular in the midway
of many summer fairs. Last summer, while strolling through a tourist area in Copenhagen, I saw a
number of these “games” being played. The hand is faster than the eye. The bettors rarely, if ever,
had a chance of winning.
Experiment No. 33
CONDUCTIVITY OF A SOLID
Place solid potassium hydroxide pellets to a depth of 2 cm in a test tube. Select a one-hole rubber
stopper that readily slides to the bottom of the test tube, and a two-hole rubber stopper that can be used
to close the test tube. Open two large paper clips so that they are linear. Insert one paper clip through
each of the holes in the two-hole stopper. Allow one of the opened paper clips to pass through the
hole in the one-hole stopper and the second paper clip to pass between the one-hole stopper and the
test tube. The one-hole rubber stopper is being used as an insulator to keep the two paper clip
electrodes separated.
Connect leads to the exposed ends of the paper clips.
Connect one of these leads to one of the terminals of a 9 volt dry cell.
Connect the other lead to one of the contacts of a miniature bulb socket.
Connect the second contact of the bulb socket back to the 9 volt dry cell.
Heat the test tube over a candle flame. Observe the effects that take place with the bulb (#46 or #47),
an LED or a buzzer as the potassium hydroxide solid begins to melt. Remove the test tube from the
candle flame and observe the results.
This experiment, together with the conductivity of solid potassium hydroxide, and aqueous potassium
hydroxide solution can be used to distinguish between the processes of ionization (of covalent
compounds) and dissociation (of ionic compounds).
Experiment No. 34
43
CONDUCTIVITY OF A GAS
This experiment is designed as a follow up to the conductivity of solids, molten solids and aqueous
solutions of solids in water. Are gases, such as HCl, ionic or covalent? What process takes place,
ionization or dissociation, when HCl dissolves water? The hydrogen chloride should be dry. If the
gas is generated in the laboratory, by the reaction of concentrated sulfuric acid on sodium chloride, it
should be dried by passing it through a "drierite" or calcium chloride drying tube before being
bubbled into the water or an organic solvent. I do not always dry the gas before using it in this
experiment.
NOTE: It is advisable that this experiment be performed in a fume hood or near a fume vent. Test the
electrical conductivity of a sample of distilled water before doing the experiment..
Bubble hydrogen chloride gas into a sample of distilled water. Use either a conductivity apparatus,
commercial or home made, to follow the conductivity of the system as the gas is bubbled into the
water.
Repeat the experiment but use an organic solvent such as cyclohexane or toluene, in place of the
water. Benzene or carbon tetrachloride actually work better but they are not allowed in most
laboratories because of their toxicity. It will be noticed that the light bulb does not light up. The
students may suggest that the hydrogen chloride gas did not dissolve in the organic solvent.
Remove the gas delivery tube from the beaker
Add some water to the gas/organic solvent system
Stir the contents of the beaker
Test the conductivity of the system again.
Make certain that the electrodes extend into the aqueous layer.
This latter step is a good example of an extraction process.
The students now have some evidence to suggest that a reaction takes place between hydrogen
chloride gas and water. The products of the reaction are hydrated ions. Chlorine gas can be used in
place of the hydrogen chloride gas. The solution of chlorine in water is also a conducting solution.
+
+
Cl (aq)
HCl(g)
+
H2O
H3O (aq)
Experiment No. 35
RIPPING CANS
A file was used to scratch the inner surface of 2 soft drink cans. The effect is to produce a break in the
plastic liner that protects the can from attack by the acids in the soft drink. Prepare one of the cans by
pouring in a solution (200 mL) containing a spoonful of copper(II) chloride dissolved in the water. Do
not do anything to the second can.
I always get a strong member of the class to try and rip the first can apart first, FOLLOWED BY A
“WEAKER” member of the class who pulls the second can apart.. The rules are simple:
Wear gloves when ripping the can.
No Twisting; just PULL the can apart.
The second (weaker) person always gets applause from the class. A good way to both introduce a
section on corrosion, and to build up the self-concept of the weaker person.
44
Take note that this experiment works better with US cans than with Canadian cans. The US cans are
aluminum while Canadian cans have a high steel content. The US cans also are thinner, and can be
forced to corrode more quickly.
This experiment was designed and made popular by Lee Marek (Weird Science)
Experiment No. 36
REACTION of ALUMINUM with COPPER(II) CHLORIDE
Experiment Number 35 can be followed up with a number of related experiments that involve the
reaction between aluminum and copper(II) chloride. The skeleton, as well as the balanced chemical
equation can be determined through a series of quantitative experiments.
2 Al(s) + 3 CuCl2.2H20(aq)
2 AlCl3(aq) + 3 Cu(s)
or, in the form of the net ionic equation,
2 Al(s) + 3 Cu2+(aq)
2 Al3+(aq) + 3 Cu(s)
Float a dry aluminum weighing dish in a beaker of water. Add a spoonful of copper(II) chloride into
the weighing dish. After a minute or two, add a squirt of distilled water into the weighing dish. After
a few minutes the students will observe the reaction and the copper deposit that appears. They will see
that the dish is almost completely used up.
Repeat the experiment, but use an aluminum dish with holes in the bottom of the dish. As the
copper(II) chloride gets wet, the reaction will start.
Prepare a beaker with a 300 mL of a dilute copper(II) chloride solution. Drop a rolled up (ball) of
aluminum foil into the solution. Observe the reactions and compare them with the two previous
reactions.
Design experiments to determine the relative (molar) amounts of copper and aluminum involved in the
reaction. How can you determine the number of molecules of water that are included in the hydrated
form of copper(II) chloride? Design an experiment to answer the question.
Experiment No. 37
SURFACE TENSION
Fill a Mason Jar with water, cover it with a piece of plastic, and invert the jar. The students are
amazed that the water stays in the jar, and the piece of plastic stays in place, holding the water in the
jar.
What keeps the water in the Mason Jar? The immediate answer is Atmospheric Pressure. Is the
atmosphere removed when the plastic card is removed from the open end of the jar? No, of course
not, so the answer must lie elsewhere.
Use a second jar, for which a plastic piece is not required in order to keep the water in the jar. The jar
is sealed with a piece of copper (or other metal) mesh, or with a piece of panty hose. The metal mesh
can be punctured with a needle, and the water stays in the jar.
45
This experiment is a good introduction to surface tension. How large can the holes be in the metal
mesh? The students can start with a fine mesh and remove some wires and repeat the test. How tall
can the jar (cylinder) actually be?
Experiment No. 38
BOTTLES and CAPS - An ANALOGY to STOICHIOMETRY
Place twenty bottles in a dishpan. Prepare six aliquots of ten caps or stoppers in each of six small
beakers. Add individual aliquots of caps to the bottles. After each addition ask "How many
individual sets of one bottle and one cap can be produced?" The terms "excess and limiting reagent"
will be indelibly imprinted on your students' minds in just a few moments.
It is not necessary to perform a long series of chemical experiments to introduce these two terms. The
important idea is the concept of "limiting" reagent. Experiments can now be performed to study the
effect of increasing the excess or reducing the amount of the limiting reagent. of the various
Experiment No. 39
EQUILIBRIUM in Cu2+(aq) SOLUTIONS
Add water slowly to a sample of crystalline copper(II) chloride, CuCl2.2H2O. A variety of color
changes can be studied by careful additions of concentrated hydrochloric acid (HCl), concentrated
ammonia (NH3), concentrated aqueous sodium chloride solution (NaCl) solution or water.
Repeat the series of experiments using copper(II) bromide or copper(II) iodide in place of the
copper(II) chloride. The reactions are reversible. Why do the colors change? What species are
responsible for the green, the blue, the yellow and the royal blue colors?
You may want to examine the colors of complex ions that have differing numbers of chloride and
water molecules involved in the ion. The chemistry is interesting and easy to demonstrate.
Experiment No. 40
TEMPERATURE EQUILIBRIUM TUBES (Commercial)
Temperature equilibrium tubes can be purchased from FLINN Scientific. They are relatively
inexpensive, the price dictates that they should only be purchased in small quantity and used by the
teacher for demonstrations. It is convenient to have 4 of these tubes for a variety of experiments.
The commercially produced tubes are made of Pyrex and are temperature-shock resistant. Place one
of the tubes in each of a series of temperature baths at 100oC, room temperature, 0oC and at a
temperature below 0oC. The cold temperature bath is prepared by mixing ice with rock salt, or Kosher
Salt (NaCl). The temperature of this cold bath can be as low as -15oC. The effect is increased if
tubes are also immersed in liquid nitrogen and/or a dry ice-acetone or alcohol bath. Pyrex tubes will
stand the thermal shock of these large temperature changes.
Demonstrate reversibility by moving the tubes from one temperature bath to another. Care must be
taken in working with the NO2/N2O4 tubes since the gases are toxic. For SAFETY purposes clamp
the tubes in a fixed position in the higher temperature baths so that they will not "jump" out of the
temperature baths.
46
The students will observe that the color of the gas increases (darker brown) with increasing
temperature and decreases (lighter brown) with decreasing temperature. Nitrogen Dioxide (NO2) is a
brown gas. Dinitrogen Tetroxide (N2O4) is a colorless gas. The N2O4 liquifies in the vicinity of
0oC, and solidifies at a temperature of approximately -10oC.
From the observations that the students make they can complete the following equation:
2 NO2(g)
N2O4(g)
plus or minus Heat
Place one or more of tubes in a refrigerator freezer in order to see the effects of warming the tube to
various temperatures.
Experiment No. 41
PREPARATION OF A "BROWN GAS"
Nitrogen dioxide/dinitrogen tetroxide gas (NO2-N2O4) can be prepared and stored in a number of
different ways. It is important that the gas be prepared and used in a well vented area preferably in a
fume hood.
If the gas is not available in a cylinder it can best be prepared by the reaction of concentrated nitric
acid on copper. In order to obtain dry gas it must be collected through a drying tube. The drying tube
can be filled with calcium chloride or with a commercial laboratory product called "drierite". This is
the method that I prefer. Most of the time I do not take the extra precaution of drying the gas since for
most of the experiments that we will do the wet gas is satisfactory.
The gas can be prepared early and stored at low temperatures, but it is safest and most convenient to
prepare the gas immediately before use. The gas can be collected in the gas bag assembly
(Experiment Number 49) and dispensed with syringes.
Put the tapered end of a Syringe Extender into the rubber delivery tube from an NO2 generator.
Attach the gas bag assembly directly to the Syringe Extender and collect the NO2 gas for use by the
teacher and/or the members of the class.
NOTE - Nitrogen dioxide gas is toxic. It must only be used in very well vented areas. In some cases
the gas can be used in syringes and then injected back into the reagent storage container. A plastic bag
assembly is useful for collecting the "used" nitrogen dioxide gas. Please note that the nitrogen
dioxide/dinitrogen tetroxide gas mixture will attack rubber and plastic. The syringes must be emptied
within 20 min of use or the rubber gasket on the plunger will start to deteriorate.
Experiment No. 42
TEMPERATURE EQUILIBRIUM (NO2/N2O4)
Home Made Apparatus
Prepare a number of test tubes with one-hole rubber stoppers, Syringe Extenders and stop cock
assemblies with Luer Locks. Use a 50 mL syringe to remove a sample of air from each tube. Replace
the air sample with the same volume of a NO2/N2O4 gas mixture.
47
Note: The tubes cannot be stored from day to day; the gas attacks the rubber stoppers. These tubes
must be prepared, used, then the gases must be discarded into a fume vent. See Experiments Number
4 and 41 for the preparation, collection and dispensing of the NO2/N2O4 gas mixture.
Prepare different temperature baths. Place one test tube into each of the baths. Compare the colors of
the gases at the various temperatures. Be careful; do not use a hot bath. The warm bath should not be
more than 50 or 60 oC. The precaution is necessary in order to avoid the chance of blowing the
stoppers out of the test tubes.
Experiment No. 43
COLORIMETRY
Prepare 500 mL of a red food coloring solution in water. Use just enough of the food coloring to
provide a definite red color to the solution. Pour the solution to a depth of 3 cm into each of four 150
mL beakers on the stage of an overhead projector.
Ask the students to predict the effect on the color of the solutions in each of the beakers if:
i) varying amounts of distilled water were added to each of the beakers
ii) varying amounts of the stock solution were added to the beakers
iii) varying amounts of the stock solution were removed from the beakers
This demonstration is an excellent introduction to calculations using the Beer Lambert Law. It is
important that the solute be one that does not undergo any appreciable change in concentration due to
shifts in equilibrium, when diluted with water. The concentration change is due entirely to the dilution
effect. The concepts developed in this experiment can be used when discussing equilibrium in
aqueous solutions.
Why do the colors appear to be different when observed from the side, and the same when observed
from the top through the overhead projector.
Experiment No. 44
REACTION OF SOLUTION A with SOLUTION B
Add 25 drops of each of solution A and solution B to 800 mL of distilled water. Stir the mixture and
divide it into six (6) equal portions in large test tubes. Note the large test tubes (30 x 300) that I use
for this experiment. The materials must be readily visible to all of the students in the class.
Predict the results of the addition of more of solution A to one of the samples.
Predict the results of the addition of more of solution B to one of the samples.
Perform the experiments and ask the students to develop a model to explain the results. Have the
students suggest other procedures that might be performed in order to verify the model.
I do not tell the students the identity of the solutions until after the demonstration and the post
laboratory discussions are completed. The identity of the reagents is not necessary to study the
predicting procedures that are involved.
48
Solution A is a relatively concentrated aqueous iron(III) nitrate solution. Solution B is a less
concentrated aqueous potassium thiocyanate solution. The actual concentrations of the solutions are
not critical since calculations are not being carried out. The teacher can experiment to get the right
concentrations. I frequently add a few drops of concentrated nitric acid to the iron(III) nitrate solution
in order to prevent the formation of an iron oxide precipitate.
The reactions can be reversed by adding samples of a chloride ion or of a phosphate ion solution. The
use of a chloride ion solution shows simple complexing reactions that can be repeated with copper ion
solutions. Try bromides and iodides as well. ...How do they work?
The solutions can be warmed and cooled in order to study temperature effects on the equilibrium
composition of the system. The changes in the colors of the samples, due to changes in temperature,
provide further evidence that equilibrium considerations are involved in this reaction.
Fe3+(aq) + SCN-(aq)
FeSCN2+(aq)
The students can now determine if the reaction, as written, is exothermic or endothermic.
Experiment No. 45
VAPOR PRESSURE IN A SEPARATORY FUNNEL
Pour 5 or 10 mL of liquid acetone into a separatory funnel (with a stopcock), and immediately close
the funnel with a stopper. Shake the separatory funnel and its contents for a few seconds. Hold the
funnel with the stoppered end down. Open the stopcock and observe the results. Close the stopcock
and repeat the shaking process; again observe the results. Repeat the process until significantly
different results are observed.
This experiment provides qualitative evidence for partial pressure and vapor pressure discussions and
comparisons. You will usually observe a completely different set of observations after 3 or 4
repetitions of the shaking process. Only after the first few shakes is any significant sound heard when
the stopcock is opened.
NOTE: The separatory funnel MUST be completely free of acetone and acetone vapor before the
experiment is repeated with another class. Why?
How does this experiment compare with the Combustion of Methanol in a large plastic bottle? See
Experiment No. 10 See Experiments No. 54, 55, 56, 57 and 58 for more quantitative experiments with
vapor pressure..
Experiment No. 46
SAFETY TIPS
SAFETY TIPS are used to insert glass tubing or thermometers SAFELY through the holes in rubber
stoppers. The SAFETY TIPS are especially useful when attempting to produce a gas-tight seal
between lengths of glass tubing and rubber stoppers. Glass tubing, of much wider diameter than the
hole through the stopper, can be inserted quite easily, and in complete safety. Use glycerine liberally
on the SAFETY TIP, the barrel of the cork borer and the hole of the rubber stopper.
Students, and teachers, should never again suffer the painful cuts that can be caused when glass tubing
and thermometers are forced through the holes in rubber stoppers.
49
The SAFETY TIPS are available from S17 Science.
Experiment No. 47
SUPERSATURATION
Fill a very clean flask with crystalline sodium acetate trihydrate, NaCH3COO.3H2O(s). Heat the flask
and contents on a hot plate until the solid just dissolves in its own water of hydration; allow the liquid
to simmer for just a moment. Be careful that the liquid does not "boil over". Allow the liquid to cool
almost to room temperature, wash down the sides of the flask with a stream of distilled water, stopper
lightly, and save for future use.
Take note that the first few times you use this system it may be necessary to reheat and cool before
use. This may be due to loss of water during the warming cycle. Spray a stream of distilled water into
the flask each time it is reheated. Once the system is used a few times it tends to remain stable.
I always take the precaution of spraying a fine stream of distilled water down the neck of the flask just
before inserting the stopper. When inserting the stopper do not force the stopper into the neck of the
flask. Allow the stopper to "fall into place". Any push will make it extremely difficult to remove the
stopper when the system cools down to room temperature. The system can now be left on the shelf for
days, weeks, months or years before it is used in class.
Show the class unlabelled flasks of saturated, unsaturated and supersaturated solutions and ask them
to predict which is which. How can the three solutions be distinguished from each other? The
common misconception is to call the saturated solution (the one with crystals on the bottom of the
flask) the supersaturated solution. This misconception can be cleared up with reference to the
equilibrium condition that exists in the flask containing the saturated solution. The students can be
“fooled” by handling the unsaturated solution very carefully, and at the same time, swirling the
supersaturated solution. Make sure that you try this before you meet the class. I always make sure
that I have a spare supersaturated solution available, just in case something unusual occurs in class.
The supersaturated solution must be stable before you try this subterfuge.
Before “seeding” the supersaturated solution have one student feel the flask to confirm that it is at
room temperature. Add one small crystal of sodium acetate trihydrate to the liquid and observe the
results. Ask the students to predict the temperature of the flask and its contents immediately after the
crystallization has taken place. This allows for an interesting review of energy considerations to be
coupled with the solubility discussion.
The resultant mass can now be heated again on the hot plate and prepared for a future use. I have used
the same sample hundreds of times. The reaction vessel must be perfectly clean. If any cloudiness
develops in the flask, filter the hot saturated solution through glass wool or cotton batting into a clean
flask and allow the system to cool to room temperature. Never cool the flask quickly; the system will
crystallize immediately due to local effects in the flask.
An interesting variation of this demonstration can be performed by preparing a number of test tubes of
the supersaturated solution. Add samples of different crystals to each of the test tubes. Be certain that
the crystals are cleaned (with distilled water) before they are added to the test tubes. Use at least one
species of a colored crystal, copper(II) sulfate, to show the effect of different solutes on the
supersaturated solution.
50
Try using commercial hot packs that can be purchased under the trade name of "REHEATER".
Many interesting experiments can be done with this product.
Experiment No. 48
MASS of a PLASTIC BAG - EMPTY and FULL
This experiments is designed to be performed individually or in pairs by students. If necessary the
experiments can be demonstrated by the teacher for the class. In each case the equipment required is
simple and relatively inexpensive. The concepts to be taught are stated following the outline.
To introduce the idea of the effect of a fluid on the apparent weight of an object immersed in the fluid.
Students are not generally aware that air is a fluid and exerts a buoyant force on objects immersed in
it.
APPARATUS and SUPPLIES
Centigram Balance (Triple Beam) or Electronic Top Loading Balance
Plastic bag, 2 L, or larger, and plastic tie (to close the bag)
1. Fold a 2 L plastic bag, place the bag and the tie in a cup on the balance.
2. Measure the mass of the cup and it’s contents.
3. Calculate the mass of air that will occupy the plastic bag. You will have to look up the density of
air at the temperature in your laboratory.
4..Wave the open bag in the air in order to fill it with air. Use the tie to secure the bag.
5. Place the bag back in the cup on the balance pan, and again find the mass of the cup and its
contents.
The students are amazed that the weight (the term weight is used, by design) of the empty bag is the
same as that of the full bag. The concept of buoyancy can be extended from immersion in water to
immersion in any fluid (air). The experimental results are very good. 2 L of air have a mass of
approximately 2.5 g. The students find that their two measurements are within 0.03 g of each other.
Therefore the air does not have mass (weight)???????
If you are teaching senior students you might ask them to design an experiment to find the true mass of
the air in an enclosed volume. See Experiment No. 50.
Experiment No. 49
PREPARATION of a GAS BAG ASSEMBLY
1. Cut a 3/4” diameter core out of a large one-hole rubber stopper.
2. Thread a 1 gallon plastic bag through the hole.
3. Spread the opening in the plastic bag and replace the 3/4” core into the large rubber stopper so
that the plastic bag is trapped between the two rubber stoppers.
4. Insert the tapered end of a syringe extender through the hole in the small (core) rubber stopper.
5. Attach a stopcock to the syringe extender.
6. Expel all of the air out of the plastic bag.
7. Attach the stopcock to a gas source.
8. Fill the gas bag assembly with the gas.
9. remove the gas bag assembly from the gas source.
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10. CLOSE the stopcock.
You now have a gas tight gas bag distribution assembly. Attach a syringe to the stopcock and
distribute the gas samples. The gas bag will contract with each sample of gas that is extracted. The
pressure inside the bag will always be the same as the external pressure. Any of the standard
laboratory gases can be distributed with this system.
Experiment No. 50
MASS of a SYRINGE FULL of GAS
The students can use a Centigram balance, a Triple Beam or an Electronic Top Loading Balance to
perform this experiment. This experiment can be used to show that air has mass, to compare the
masses of equal volumes of gases, and to determine the molar masses of various gases. This
experiment MUST be performed by pairs of students. It is essential that the procedure be
demonstrated carefully before the students start working in order to make sure that the equipment is
not damaged through improper use.
APPARATUS and SUPPLIES
Centigram Balance (Triple Beam) or Electronic Top Loading Balance
140 mL plastic syringe, with a hole drilled in the plunger
3" or 4" nail
Stopcock or Syringe Lock (There are a number of types available)
1. Prepare a 140 mL plastic syringe by drilling a hole in the plunger 1 cm from the rubber gasket.
The diameter of the hole is determined by the diameter of the nail (3" or 4" in length) that will be
positioned through the hole.
2. Secure the Stopcock firmly on the tip of the syringe.
3. One student must hold the syringe firmly, with both hands, while the second student withdraws
the plunger far enough to expose the hole in the plunger. The nail is inserted through the hole so
that it extends over both edges of the syringe barrel.
This process must be practiced before the Stopcock is placed on the tip of the syringe. It is important
that the nail be positioned properly so that it does not enter the barrel of the syringe and destroy the
syringe.
4. Place the syringe on the balance pan and determine the mass of the empty (evacuated) syringe.
5. Open the Stopcock and allow air to fill the syringe.
The teacher, to satisfy his/her curiosity, may want to calculate the mass of air that will fill the syringe,
and compare that with the measured quantity.
6. Replace the syringe assembly (including the nail, still in same position through the hole in the
plunger) on the balance pan and determine the mass of the full syringe assembly.
7. Determine the mass, and volume, of the enclosed air sample.
The data obtained in this experiment is within a few percent of that expected by calculation. The
experiment can be performed by a full class within only a few minutes. It is NOT necessary to apply
buoyancy corrections since the volumes of the EMPTY and the FULL syringe are identical. Repeat
the experiment with any other gases that are available in the laboratory. Take note that each group of
students requires only 140 mL of each gas.
Molar masses can be determined for the gases Oxygen, Hydrogen, Carbon Dioxide, and the burner gas
that is used in the laboratory. An interesting modification of this experiment would be to have the
52
students use the experiment to determine the identity of the burner gas, or any other unknown gas
sample. It is also possible to use this experiment and this apparatus to determine the equilibrium
constant for the NO2-N2O4 system. See Experiment No. 59.
Experiment No. 51
USE of the VARI STOP SYRINGE - for ALL EXPERIMENTS
Open the syringe to approximately 15 mL..
Hold the syringe in one hand and place the fingers of the other hand on the fins of the syringe
plunger.
Twist the plunger gently (about 15o); you will feel slight resistance to the twisting action. If
you hear a clicking sound you may have gone too far, but you will find that out in a moment or
so.
Try, gently, to close the syringe. It should not close. Do NOT force it.
The syringe is in the CLOSED position.
Twist the fins in the other direction; the syringe can be closed easily.
The syringe is now in the OPEN position.
Experiment No. 52
PRESSURE - VOLUME RELATIONSHIPS in GASES
Pairs of students perform a Boyle's Law Experiment in which they measure the pressure and volume
of a gas sample directly.. Take note that mercury is NOT used in any of the experiments.
APPARATUS and SUPPLIES
Pressure gauge
Plastic syringe
20 mL VARI-STOP syringes are the best ones to use for this experiment
Support stand and clamp
1. Moisten one end of the rubber tubing and slip it over the tapered end of the syringe extender, and
force it as far as possible. Ideally the plastic syringe extender will be in contact with the metal
nipple of the pressure gauge.
2. Moisten the other end of the rubber tubing and slip it over the inlet nipple of the pressure gauge.
Force the rubber tubing as far as possible over the nipple, touching the metal nipple of the gauge,
if possible.
3. Attach the stopcock to the syringe extender. Tighten the Luer Lock connectors - make the fitting
finger tight.
4. CLOSE the stopcock. The handle should now be perpendicular to the length of the stopcock. To
protect the pressure gauge the stopcock will ALWAYS be in the CLOSED position, except when
indicated in this procedure. The stopcock must be CLOSED whenever the apparatus is being
manipulated.
5. OPEN the stopcock.
6. Extend the syringe to the 20 mL position.
53
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
CLOSE the stopcock
Attach the syringe to the stopcock - finger tight.
OPEN the stopcock.
CLOSE the stopcock.
Read and record the pressure indicated on the pressure gauge and the volume of gas (air) trapped
in the syringe. The pressure reading should be ZERO, but please take note that this is the
GAUGE Pressure. The actual pressure, in all cases, is atmospheric pressure plus the gauge
pressure.
CLOSE the stopcock.
Change the volume of gas in the syringe by pushing the plunger in very slightly - to
approximately 19 mL.
OPEN the stop cock.
CLOSE the stopcock.
Read and record the pressure indicated on the pressure gauge and the volume of gas (air) trapped
in the syringe.
Continue changing the volume of the enclosed air sample until at least 6 sets of data are collected
and recorded. NEVER allow the reading on the pressure gauge to exceed 400 mm (52 kPa)
pressure.
NEVER extract air from the system, thus causing a negative pressure on the gauge.
The students can now be instructed to plot the pressure and volume data on a graph and/or to calculate
the pressure-volume products for each set of data points. The experiment can be repeated with other
gases that are available in the laboratory in order to show that the pressure - volume relationship
determined for air samples is also applicable to all other gases.
Experiment No. 53
PRESSURE - TEMPERATURE RELATIONSHIPS in GASES
Students will perform a Charles' Law type of experiment in which they will measure the pressure and
temperature of a gas sample directly. Each of the gas law experiments that follow should be
performed by pairs of students. Take note that mercury is NOT used in any of the experiments.
APPARATUS and SUPPLIES
Pressure gauge
1 L Florence flask
Thermometer
Two holed rubber stopper to fit the flask
Hot water, heat source, ice cubes
Support stand and two clamps
6 cm length of glass tubing
5 cm length of rubber tubing, 1/8" inner diameter
Large enough beaker so that the flask can be immersed in the beaker
Flask (each pair of students might have a different size of flask)
1. Insert the thermometer into one hole in the 2 hole rubber stopper (Use
SAFETY TIPS –
See Experiment No. 46).
2. Insert a length of glass tubing (fire polished), or a syringe extender through the second hole in the
2 hole rubber stopper (Use SAFETY TIPS).
3. Insert the rubber stopper securely into the mouth of the flask.
4. Clamp the flask into position on the support stand.
5. Use a 5 cm length of rubber tubing (inner diameter 1/8") to connect the pressure gauge to the
glass tubing (or the syringe extender) through the second hole in the rubber stopper.
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6. Measure and record the temperature of the gas in the flask. Take note that the gauge pressure is
zero and hence the pressure of the gas in the flask is atmospheric pressure.
7. Heat the flask and the gas to the highest temperature that can conveniently be read on the
thermometer. Record the temperature and the pressure of the gas. The flask can be heated by
immersing it in a water bath in the large beaker, or by heating it directly with a gentle flame.
Take note that the thermometer is inside the flask, hence the temperature recorded on the
thermometer is the temperature of the enclosed air. The actual temperature of the water in the
heating bath is not significant since the gas temperature has been recorded.
8. Cool the water bath by adding ice cubes. Make at least 10 pairs of pressure-temperature readings.
9. Plot the pressure-temperature data on a graph.
NOTE: If side arm flasks are available then use one-hole rubber stoppers in place of the 2 hole rubber
stoppers.
Analyze the data by extrapolating the temperature-pressure graph to zero pressure. This gives an
approximation of Absolute Zero similar to that produced by extrapolating a temperature-volume graph
to zero volume.
Repeat the experiment using gases other than air in the flask. Students learn that the
pressure/temperature relationships are independent of the gas under consideration. The experiment
can be used as an introduction to the IDEAL GAS LAW.
Each student, or group of students can do the experiment using flasks of different volumes.
Experiment No. 54
PARTIAL PRESSURE of a GAS in a FIXED VOLUME
Students will perform a series of experiments to study the effect of adding aliquots of a gas to a sample
of the gas in a fixed volume. The effect of changing the volume of the vessel will also be studied. In
Experiment No. 55, this will be expanded to a study of Dalton's Law of Partial Pressures. The
experiments will ALL be carried out without using mercury manometers.
APPARATUS and SUPPLIES
Pressure gauge
Two-hole rubber stopper to fit the flask
Support stand & two clamps
2 syringe extenders
2 plastic stopcocks
2 syringe extenders
Florence Flask (each pair of students can have a different size of flask)
1 five cm length of rubber tubing, 1/8" inner diameter
1.
2.
3.
4.
6.
7.
8.
9.
Insert the tapered ends of two syringe extenders into the holes of the 2-hole rubber stopper.
Insert the rubber stopper securely into the mouth of the flask.
Clamp the flask into position on the support stand.
Use a 5 cm length of rubber tubing (inner diameter 1/8") to connect the pressure gauge to one
of the syringe extenders extending through the holes in the rubber stopper.
Connect a stopcock to the Luer Lock end of the second syringe extender.
CLOSE the stopcock.
Connect a stopcock to the syringe that will be used for injecting gas into the flask.
OPEN the stopcock on the syringe assembly and fill the syringe with 20 mL of air; CLOSE
the stopcock.
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10. Connect the stopcock on the syringe to the stopcock on the flask assembly.
11. OPEN both stopcocks; compress the syringe to force the gas from syringe to the flask;
CLOSE both stopcocks.
12. Read and record the pressure indicated on the gauge and the volume of gas injected into the
system. The pressure of the gas in the flask is now atmospheric pressure plus the pressure
shown on the manometer gauge.
13. Remove the syringe and stopcock assembly from the flask assembly
14. Repeat steps 9 to 13 as many times as necessary. Protect the pressure gauge; do NOT allow
the gauge pressure to read more than 400 mm (52 kPa).
15. Repeat the experiment using different sizes of flasks.
16. Repeat the experiment using different volumes of air.
17. Repeat the experiment using different gases.
18. Repeat the experiment but use different gases for each addition to the system.
As result of this experiment the students should be able to verify Boyle’s Law again, and also discover
(investigate) Dalton’s Law of Partial Pressures.
Experiment Number 55
EFFECT on PRESSURE of ADDING LIQUID to a GASEOUS SYSTEM
Students will perform a series of experiments to study the effect of adding a sample of a volatile liquid
to air in a fixed volume. The effect of changing the volume of the vessel will also be studied. This
leads directly to the vapor pressure of liquids. In the next series of experiments, this will be expanded
to a study of the effect of temperature on the vapor pressure of a liquid and of the effect of adding
other liquids, miscible and immiscible, to the system. The experiments will ALL be carried out
without using mercury manometers.
APPARATUS and SUPPLIES
Pressure gauge
500 mL Florence Flask
1000 mL Florence Flask
Two-hole rubber stopper to fit the flask
Support stand and two clamps
2 syringe extenders
1 five cm length of rubber tubing, 1/8" inner diameter
2 plastic stopcocks
2 syringe extenders
25 mL of methanol in a small beaker
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Insert the tapered ends of two syringe extenders into the holes of the 2-hole rubber stopper.
Insert the rubber stopper securely into the mouth of the flask.
Clamp the flask into position on the support stand.
Use a 5 cm length of rubber tubing (inner diameter 1/8") to connect the pressure gauge to one
of the syringe extenders extending through the holes in the rubber stopper.
Clamp the pressure gauge to a support stand.
Connect a stopcock to the Luer Lock end of the second syringe extender.
CLOSE the stopcock.
Connect a stopcock to the syringe that will be used for injecting liquid into the flask.
OPEN the stopcock on the syringe assembly and draw 10 mL of methanol into the syringe;
CLOSE the stopcock.
Connect the stopcock on the syringe to the stopcock on the flask assembly.
56
11. OPEN both stopcocks; compress the syringe to force the methanol from the syringe into the
flask; CLOSE both stopcocks.
12. Watch the pressure change for approximately 10 min. Record the highest partial pressure
observed on the pressure gauge.
13. Read and record the pressure indicated on the gauge and the volume of liquid injected into the
system. The pressure of the gas in the flask is now atmospheric pressure plus the pressure
shown on the manometer gauge.
Ask the students to predict the pressure gauge readings if the experiment were repeated with a larger
(1000 mL) or smaller (250 mL) flask. The students will predict that the pressure will be double in the
smaller flask, and one-half the first result in the larger flask. These predictions are in line with Boyle’s
Law and the IDEAL Gas Law.
Repeat the experiment using the larger flask.
The students are surprised to see that the partial pressure of acetone is independent of the size of the
flask. It is important that sufficient acetone be in the flask so that some excess acetone remains on the
bottom. It is now possible to relate equilibrium considerations to the vapor pressure of liquids.
Experiment No. 56
EFFECT of TEMPERATURE on VAPOR PRESSURE of a
LIQUID……..QUALITATIVE
The students or the teacher will perform an experiment to study the effect of cooling an acetone
liquid/vapor system from room temperature to the temperature of an ice-water bath. The experiments
will ALL be carried out without using mercury manometers.
This experiment can be performed with the same equipment that was used in Experiment Number 55.
The only additional piece of equipment required is a container larger enough to house the flask used in
the previous experiment and a supply of ice cubes.
Repeat Experiment Number 55 steps 1 to 13.
14.
15.
16.
17.
Place the large beaker in position so the flask can be almost fully immersed in the beaker.
Fill the beaker with an ice-water mixture
Observe the reading on the pressure gauge over a 10 min period
Once the ice-water bath begins to warm up be careful to remove the stopper from the flask to
prevent a pressure buildup which will expel the stopper from the flask.
I ask the students to predict/calculate the total pressure of the acetone and the air in the flask once the
temperature of the acetone-air mixture reaches 0oC. The students make Charles' Law types of
predictions and they will calculate that the total pressure will drop to approximately 273/298 of the
original pressure. They are surprised to see that the total pressure in the flask drops to a value below
atmospheric pressure. It is now possible to discuss the reasons for this drastic change. In addition to
the Charles' Law effect, the vapor pressure of a liquid shows marked changes with temperature. The
next series of experiments is designed to study that effect.
Experiment No. 57
57
EFFECT of TEMPERATURE on VAPOR PRESSURE of a
LIQUID………..QUANTITATIVE
The students or the teacher will perform an experiment to study and plot the effect of cooling an
acetone liquid/vapor system from room temperature to the temperature of an ice-water bath. The
experiments will ALL be carried out without using mercury manometers.
This experiment can be performed with the equipment used in Experiment No. 56. The only
additional pieces of equipment required are a thermometer and a three-hole rubber stopper
Use a three-hole rubber stopper in place of the two-hole rubber stopper used in Experiment Number
56. Set up the equipment exactly as done in Experiment Number 56. In the third hole of the rubber
stopper insert a thermometer. Use SAFETY TIPS to insert the thermometer.
Repeat Experiment Number 56. When equilibrium is established slowly change the temperature of the
flask by cooling with ice cubes, and then heating gently with a burner flame. Record the temperatures
and pressures at regular intervals. Do not allow the temperature of the methanol to exceed 35oC, or to
fall below 10oC.
Experiment No. 58
EFFECT on VAPOR PRESSURE of ADDING ADDITIONAL
LIQUIDS to the SYSTEM
The students or the teacher will perform an experiment to study the effect on pressure of adding
miscible and immiscible liquids to a liquid/vapor system. The experiments will ALL be carried out
without using mercury.
Repeat Experiment Number 56 steps 1 to 13 with three identical sets of experimental equipment.
Repetition 1
Repetition 2
Repetition 3
Liquid to be injected
Liquid to be injected
Liquid to be injected
Methanol
Toluene
Water
Record the vapor pressure measured for each of methanol, water and toluene.
Inject samples of water to Repetitions 1 and 2.
Water and methanol are miscible in all proportions.
Water and toluene are immiscible in all proportions.
58