The Effect of Temperature on the Rate of Reaction Rate of Alka Seltzer™ in Water
Purpose
To study the effect of temperature on the reaction rate of Alka Seltzer™ in water.
Background
The rate of reaction is the time required for a given quantity of reactants to be turned into
product(s). The rate of reaction is determined by many factors including the nature of the
reactants, the concentration of the reactants, the temperature, the presence or absence of a
catalyst, and the pressure (for reactions involving gases).
Alka Seltzer™ tablets contain heat-treated sodium bicarbonate, citric acid, and a salicylate
analgesic. When the tablet is placed in water, the following reaction occurs:
3NaHCO3(s) + C3C6H5O7(s) + H2O(l) → C6H5O7Na3(aq) + 4H2O(l) + 3CO2(g)
Design an experiment to study the effect of temperature on the reaction rate of Alka Seltzer™ in
water. Check with the instructor regarding how many Alka Seltzer™ tablets are available for
each team.
Procedure
Design an experiment to determine the relationship between temperature and the rate of the
reaction.
Safety Information
1. Do not stopper or cover the container in which the reaction is taking place.
2. Keep the temperature of the water between 5oC and 85oC.
3. After reviewing your procedure, the instructor will discuss any safety precautions that are
specific to your experiment.
Questions for Further Thought
1. What are some other variables that could affect the rate of this reaction?
2. What factors might make one type of effervescent tablet more effective than another?
Teacher Notes
Alka Seltzer™ tablets provide a relatively safe and inexpensive way for students to study many
aspects of reactions. In this lab, students will investigate the effect of temperature on the rate of
the reaction.
1. Students must first decide on the volume of water to use in each trial. Small volumes will
not allow the reaction to go to completion. Students can use trial and error, or you can
suggest they use 100 mL of water.
2. Students may have trouble deciding when the reaction is finished. The important thing is
that the teams be consistent in determining the end of reaction for each trial.
3. Effervescent tablets other than Alka Seltzer™ can be used.
4. You may want to give students one tablet for a trial run.
Options
1. The Clock Reaction is a good preliminary demonstration for this experiment. This
demonstration involves mixing two solutions and, after a time, a dramatic change in color
will occur. Perform the demonstration using reactants at two different temperatures to
show the change in time for the color change.
2. To spend less time on the experiment, have each team pick a different temperature to
study and then pool their results.
3. Students could also investigate the effect of changing surface area on the rate of this
reaction.
4. Instead of only investigating the role temperature plays in this reaction, let the students
compete to see who can get the tablet to react in the shortest amount of time. Students
could vary temperature, volume of water, surface area of the tablet, and so on.
Time
Time needed to design the experiment should be around 15 minutes if the students are familiar
with the water displacement technique. Time needed to run the experiment should be 30 minutes.
Materials
Require the use of goggles, gloves, and aprons/lab coats. The following supplies should be
readily available:
 Alka Seltzer™ (3 to 4)
 Stop watch
 250-mL beakers
 Tongs
 Thermometers
 100-mL graduated cylinder
 Hot plate or other heat source
 Mortar and pestle
 Ice
Sample Procedures
1. Students may add one tablet to a given amount of water that has been heated or cooled to
various temperatures and time the reaction.
2. Students might grind the tablets in a mortar and pestle and add a certain mass of crushed
tablet to a given amount of water that has been heated or cooled and time the reaction.
This will ensure that each trial uses the same mass of tablet.
3. Students might determine the mass of the tablets ahead of time to determine if all tablets
have the same mass. If the mass varies, they may convert the data to sec/g of tablet.
Common Misconceptions, Procedural and Calculation Errors
1. Students might assume all tablets have the same mass.
2. Students might use different thermometers for each trial.
3. Students might add ice to a given amount of water to cool it below room temperature to
cool it to a lower temperature and then not re-measure the volume of the water before
adding the tablet. This will result in a volume that is not consistent between trials.
Lab Report
A lab report should include the following sections:
I.
Title
II.
Purpose
III.
IV.
V.
VI.
VII.
VIII.
Materials
Procedure
Data
Calculations
Conclusions (including a discussion of sources of error
Answers to the Questions
Answers to Questions
1. Other factors that might affect the rate of this reaction include the surface area of the
tablet, the volume of water, or the purity of the water.
2. The quantity and quality of the active ingredients could give one type of tablet more
effective at pain relieve than another. The rate of reaction shouldn’t be a major factor in a
tablets effectiveness because the person does not take the medicine until the reaction is
over.