Chapter 2, Problem 2CHQ

Materials Needed:

• Alka-Seltzer tablets (8)
• 1/4 cup of water
• 2 small plastic cups
• Sealable plastic bag (1)
• Kitchen scale

Can you observe the law of conservation of matter if a gas is produced in a chemical reaction?
The law of conservation of matter states that atoms are not created or destroyed during a chemical reaction. For your experiment, we are challenging you to demonstrate this law through the dissolution of Alka-Seltzer tablets in water.
Alka-Seltzer tablets function as an antacid and pain reliever, with aspirin as the analgesic. When the tablets are dissolved in water, citric acid and sodium bicarbonate are dissolved and react to form water and carbon dioxide. The formed sodium citrate and aspirin are dissolved in the water and can be consumed to help with heartburn and pain relief. In this experiment, you can observe whether or not atoms are lost in the reaction, and, therefore, you are observing the law of conservation of matter.
First, measure 1/3 cup of water into a small plastic cup. Record the weight of the water and the cup using a kitchen scale. (Hint: set it to grams.) Drop 4 Alka-Seltzer tablets into the water and immediately record the total weight. Write down your observations as the tablets dissolve in the water. What observations can you make about the mixture?
After the reaction is completed, measure the final weight of the mixture. Did you see a difference in the weight before and after the reaction?
For the next step, run the reaction again, but this time, place both the 1/3 cup of water and the 4 Alka-Seltzer tablets on opposite sides of the plastic bag. Seal the bag and then move the Alka-Seltzer tablets into the cup of water. Be sure to record the total weight of the mixture in the bag before and after the reaction.
2. Did you see a change in the weight of the mixture in the sealed bag? Why or why not?