Notes

Background:

The reaction you will be investigating is the reaction that occurs when an Alka-Seltzer tablet is placed into a given amount of water. Alka-Seltzer is an over-the-counter antacid and pain relief medication that is dissolved in water before it is ingested. Each tablet contains aspirin (acetylsalicylic acid), citric acid, and sodium bicarbonate. As the tablet dissolves in water, the bicarbonate ions in the tablet react with the hydrogen ions from the acids that are also contained in the tablet. The carbon dioxide gas produced by the reaction is what causes the bubbling that can be observed.

HCO3- (aq) + H+ (aq) → H2O (l) + CO2 (g)

In this investigation, you will design two experiments which will compare two different factors that may affect the rate of the Alka-Seltzer reaction. Possible factors to be investigated include temperature, surface area, agitation, and amount of reactants. Remember to make sure there is only one independent variable in your experimental design for each experiment. You can only test one factor at a time.

The document you submit to your instructor should include the following sections: materials, procedure, and conclusion. Instructions and suggestions are provided below to help you make sure that each section of your document is complete.

Materials:

Alka-Seltzer tablets
Empty and clean water or soda bottles (12 oz to 24 oz)
Balloons (to capture the carbon dioxide gas produced)
Water
Clock
Additional materials may be required, depending on your lab design.
Procedure:

Design two experiments that will compare two different factors that may affect the rate of the Alka-Seltzer reaction. Possible factors to be investigated include temperature, surface area, agitation, and amount of reactants. Remember to make sure there is only one independent variable in your experimental design for each experiment. You can only test one factor at a time. You will need to have two separate procedures for each factor tested.
Be sure to write a detailed procedure for each lab design so that the same procedure can be followed accurately by anyone who reads it. Include details on the setup, the control of variables, and how the rate of each trial will be compared.
For each of your two reactions, most of the reactants and products can be difficult to see, and concentration can be difficult to measure without the proper laboratory equipment. Therefore, it is recommended that the volume of carbon dioxide gas produced over a given amount of time be used to help qualitatively compare the reaction rates of each trial. If you have another way you would like to compare rates of this reaction, feel free to explain it thoroughly in your written lab procedure.
Be sure your instructions include multiple trials for each factor to help ensure that the results of your investigation are more reliable.
Discussion and Conclusion:

Answer the following questions in complete sentences.

What two factors did you investigate in your procedure, and why did you choose to compare these two factors?

What other factors did you need to control during your investigation? Explain how you controlled each one in your procedure.

What was your prediction about the results of each factor tested in your two lab procedures? Explain your predictions based on your knowledge of the dissolving process, collision theory, and reaction rates.

In your own words, explain the collision theory, and what is necessary for a collision to be successful.

A specific catalyst was not provided for this reaction, but catalysts are useful for increasing the rate of many slow reactions. In your own words, give a detailed explanation of how catalysts can increase the rate of a reaction or process.