Question

Alka Seltzer Poppers

Alka Seltzer is sometimes taken for acid indigestion. This over-the-counter medication is taken differently than most others since it is added to water before ingesting, rather than being “washed down” with the water. Let’s investigate this addition of Alka Seltzer to water.

Materials

5 (or more) Alka Seltzer® tablets

clear container such as a plastic cup or glass

room-temperature water

1 35-mm film canister with lid

teaspoon measure

tablespoon measure

ice-cold water

very hot tap water

safety goggles

(optional) 1/4-cup measure

Safety

Goggles are recommended to protect your eyes from possible flying debris in this activity. Do not use water hot enough to scald.

Exploration

Step 1 Determine and record the active ingredients of Alka Seltzer tablets.

Step 2 Add about 1/4 cup of room-temperature water into a clear container. Add an Alka Seltzer tablet to the water and observe. Keep the solution for use in Step 3. Describe what happens. What role does water play in this system? What is the identity of the most obvious product of this chemical change? Write the chemical equation which describes the reaction that has occurred.

Step 3 Place 1 tablespoon of the solution from Step 2 in the film canister. Add half an Alka Seltzer tablet to the canister and immediately put on the lid. Hold the canister upright and away from your face. What happens? Explain your observations.

Step 4 Design and perform an investigation to determine if the observations in Step 3 are reproducible. What did you do? What did you find out?

Step 5 Repeat Step 3 with room-temperature water which has not had an Alka Seltzer tablet dissolved in it already. How do the results compare with those in Step 3?

Step 6 Rinse out the canister and place 1 teaspoon of room-temperature water in it. Add half an Alka Seltzer tablet to it and immediately put on the lid as before. Compare your observations with those in Step 5 and explain any similarities and differences

Step 7 What do you think would happen if you added 2 tablespoons of water to the canister before adding the Alka Seltzer? Try this variation using the same technique and explain your observations.

Step 8 Design an experiment to determine the impact of changes in the temperature of the water on the system. Do not use water hotter than hot tap water or colder than ice water. Describe what you did and your observations. Explain what you observed.

Step 9 Which trial is the control, the one to which the other trials are compared? Why is the number of variables changed important? What other variables might be studied in this system?

Challenge

What are the effects of changing the volume of water and the temperature of the water used in the investigation?