VANDERBILT STUDENT VOLUNTEERS FOR SCIENCE
http://studentorgs.vanderbilt.edu/vsvs
Rates of Reactions Using Popping Film
Canisters
Spring 2005
Purpose: To correlate changes in the time it takes to pop a film canister with experimental
variables. This experiment uses Alka-Seltzer tablets.
Introduction: A standard fun activity is to place a piece of alka seltzer tablet in a film canister
with some water, and hold the canister until the lid pops off. Today's activity is based on
measuring the length of time it takes for the lid to pop off when different (temperature)
conditions are present.
The active ingredients of Alka Seltzer tables are sodium bicarbonate (baking soda), citric
acid, and aspirin (acetylsalicylic acid). Bubbles of carbon dioxide gas are produced whenever an
acid is added to baking soda. In the present case, there are two acids - citric acid and aspirin - so
there are two reactions producing carbon dioxide - the one between baking soda and citric acid
and the one between baking soda and aspirin. Alka Seltzer is an anti-acid because both the
sodium citrate and the sodium acetylsalicylate neutralize the excess stomach acid. The
carbonation produced by dissolving carbon dioxide gas in water also settles the stomach - as
anyone knows who drinks a carbonated soft drink to treat a mild stomach upset.
Materials - enough for 15 pairs
4
Packets of Alka-Seltzer tablets
1
knife for scoring tablets
15
2oz containers
15 bags containing:
1 25 mL graduated cylinder
1 film canister--each film canister and its lid are numbered to make a matched set
1 small plastic funnel
1 clear plastic cup (6oz)
1 4-oz bottles of water
15 16oz cups (for making ice water)
15 stopwatches -each with a CD tag that is numbered
1 styrofoam container of ice
15 aluminum pans
2 16-oz bottles for water (fill at the school)
1 plastic tub for waste solutions.
2 rolls of paper towels
30 observation sheets
30 pencils (for Afterschool groups )
1
Set-up
One VSVS member needs to score several Alka Seltzer tablets in half and gently snap them.
Repeat so that there are enough for each student pairs to have 7 ¼’s. Place the 7 ¼’s in a 2 oz
container (1 per pair).
Fill the 16oz cups with ice and fill with water at the time the students are ready to do Experiment
2.
Give each pair one of the bags, a stopwatch, 1 pie pan, 1 observation sheet, and five sheets of
paper towel.
MAKE SURE YOU GET ALL OF THE STOPWATCHES BACK AT THE END OF THE
LESSON. Each stopwatch has a big tag with a number.
Do not let students do anything other than the designated experiments. Each film canister and
its lid is numbered to prevent mix-ups during the experiments. If a lid blows off and falls away
from the work area, make sure that the retrieved lid number matches the canister number.
• Have students carry out the following steps.
Take the clear cup and half fill with water.
Add a piece of Alka Seltzer tablet to the water and observe what happens.
Ask them to answer the following questions:
What happens? Bubbles of gas are coming off.
What gas is given off? Carbon Dioxide, CO2
Why? Sodium bicarbonate reacts with acid (citric acid, aspirin) to give CO2
DIRECTIONS FOR USE OF STOPWATCH AND FILM CANISTERS
This experiment involves timing how long it takes for the lid of the film canister to blow off.
The student holding the stopwatch should start the stopwatch when the lid is placed on the
canister and stop it when the lid blows off. The student holding the film canister should hold
onto the sides with the lid pointed upward and away from his face (and not pointed at any other
student).
Have the students that are going to be using the stopwatch try starting and stopping the
stopwatch to make sure they know how to do it.
Do a "dry run” without the Alka Seltzer tablet to make sure the student can get the lid on
all the way - a good approach would be for the student putting on the lid to say "start”
when the stopwatch should be started.
Have students repeat each experiment three times and record their observations on the
observation sheet.
Have students empty their film canisters and rinse water in the plastic tub. One VSVS
volunteer should empty the tub if it gets too full before the end of the experiment. Also
empty the tub in a sink in the room or in a restroom before bringing the kit back.
2
PART I
EXPERIMENT 1
Tell the pairs to:
• assign one partner to use the stopwatch while the other student adds the quarter of an AlkaSeltzer tablet to the film canister.
The student holding the stopwatch will start the stopwatch as soon as the other student
has put the lid on the canister.
The stopwatch should be stopped when the lid of the canister blows off (or gently pops
off!).
• measure out 15 mL of room – temperature solution using the 25-mL graduated cylinder and
a funnel.
• add the 15 mL to the film canister.
• make sure that the timekeeper is ready.
• drop a ¼ piece of Alka-Seltzer tablet into the canister and immediately press on the lid
(FIRMLY).
• record the time on the observation sheet.
• after each trial, the students should bring their film canister to the tub dump out the contents
and rinse out with a little water.
• repeat the experiment two more times and record observations.
EXPERIMENT 2
• Give each pair a cup of ice water. (Ice water is made by a VSVS member at the beginning of
the lesson by filling 15 16-oz cups half-full of ice and adding enough water to fill the cup.
• Repeat Experiment 1 use 15 mL of ice water.
• Students should record the times on the observation sheet for the three trials, and compare their
results to those from Experiment 1.
STOP AT THIS POINT TO DISCUSS THE RESULTS SO FAR.
Ask students which experiment should be the control experiment (the one that other results are
compared to). Why?
Answer: One variable is altered – temperature of the water.
Experiment 1 should be the control experiment.
Ask students to give you their times for Experiments 1 and 2 and then ask them to explain why
the times are different.
Here are some sample data.
Experiment 1: 9.5, 8.7, 8.4, 7.2
Experiment 2: 27.9, 27.6, 21.9, 25.7
There will probably be variations of data from one team to the next, but when each team
compares its own data for the two experiments, they should find that Experiment 1 is faster than
Experiment 2.
3
First, ask students to explain why Experiment 2 is slower than Experiment 1 - the only difference
is using ice water instead of room temperature water.
Answer: The speed of chemical reactions decreases with a decrease in temperature.
Therefore, the reaction of the acids in Alka-Seltzer with the sodium bicarbonate in Alka-Seltzer
to produce carbon dioxide gas is slower in the ice water. Another factor is the greater solubility
of gases at lower temperature than at higher temperature. In the present case, about 2 to 3 times
more carbon dioxide can dissolve in cold water than in room temperature water, and this would
leave less gas available for building up pressure to blow off the lid. As a result, it will take
longer for the lid to blow off.
Part II – OPEN-ENDED EXPERIMENTS
Ask the students if there are other variables that could alter the time it take for the lid to “pop”.
Example could be:
Vary the amount of water used, vary the size of the tablet….
Emphasize that there must be only one variable. Room temperature water should be used and
the results should be compared to the times obtained in experiment 1.
Lesson written by
Dr. Melvin Joesten, Faculty Advisor of VSVS, Vanderbilt University
Pat Tellinghuisen, Coordinator of VSVS, Vanderbilt University
Stacy Tellinghuisen, lab assistant
Part I of this lesson is based on the article by A.M. Sarquis and L.M. Woodward, "Alka Seltzer Poppers: An
Interactive Exploration," Journal of Chemical Education, Vol. 76, pp. 385-386, March, 1999.
4
Observation sheet - Popping Film Canisters
Name______________________________
Table 1
The effect of different reactants on the speed of chemical reactions
Reactants
Trial 1
Speed of chemical reaction(s)
Trial 2
Trial 3
mean
½ tablet +
15mL water
(room temp)
½ tablet +
15mL water
(ice temp)
5
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