# Lab: Alka Seltzer Time Bombs

Lab: Alka Seltzer Time Bombs

Chemistry

Prelab Questions:

1. Describe how the rate of a reaction can be measured.
2. What can be changed with regards to temperature, concentration and surface area to increase the rate of a reaction?
3. What will you observe in the lab?
4. What conditions will be varied in the lab?

Procedure:

1. Obtain a film canister, a graduated cylinder, a thermometer, a mortar and
pestle, a scoopula and 6 Alka Seltzer tablets. Also have on hand a stopwatch.
2. All trials will be performed using 10 mL of water and one entire tablet of Alka Seltzer.
3. Clean up by rinsing all chemicals in the sink and returning lab material where you found them.

Part A: Changing the Water Temperature

1. In the first trial, add cold water to the canister. Take the temperature of the water. Record this in data table 1.
2. When ready to start the reaction, drop a tablet of Alka Seltzer into the canister and quickly cap it. Start timing until the top of the container pops off. Record your time in seconds in the data table. ***Do not look directly down at the canister when filled! Stay a couple of feet away. Safety first!
3. Rinse the mixture down the sink. Repeat the trials using room temperature and hot water.

Part B: Changing the Surface Area

1. Using tap water, dissolve a whole tablet of Alka Seltzer in the canister.
2. Instead of using a whole intact tablet, use the mortar and pestle to crush the tablet. Get as much of the powder onto a scratch paper to pour into the canister.

Temperature of Water (°C) / Time (seconds)
Cold
Room
Hot

Data Table 1:

Time (seconds)
Whole Tablet
Crushed Tablet

Data Table 2:

Analysis and Applications

1. Create a line graph (at least half-a-page large) comparing the time it takes to pop with the temperature of water used. Place the temperature of water on the x-axis & the time on the y-axis. Be sure to label all axes & give the graph a title.
2. Based on your graph, what is the relationship of the rate of the reaction compared with the temperature of the water?
3. What do you think would have happened to the reaction time if you reduced the size of the tablet by half?
4. If you wanted the reaction to go faster without changing the temperature of the water or the surface area, what could you do instead?
5. If you wanted to scare your friends by sneaking up on them as quickly as possible, what combination of temperature and surface area would you try? Using your last tablet, try this! (Not to scare your friends!) What was the time it took for the cap to pop? Was it faster than changing the temperature or the surface area alone?