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Student Guide: Plop, Plop, Fizz Fast: The Effect of Temperature on Reaction Time

Downloadable and printable Student Guide PDF.
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Summary

Have you ever seen an Alka-Seltzer tablet make bubbles in water? Have you wondered if how fast those bubbles form is always the same or if it changes based on the temperature of the water? Find out using Alka-Seltzer tablets, jars of hot and cold water, and a stopwatch.

Useful Vocabulary

  • Alka-Seltzer: A medical drug that works as a pain reliever and an antacid. It has aspirin, baking soda, citric acid, and other ingredients.
  • Antacid: Something that helps neutralize stomach acidity. For example, heartburn can be caused by too much stomach acidity, and an antacid can help relieve this.
  • Baking soda: Chemically known as sodium bicarbonate (NaHCO3), it is used in Alka-Seltzer as an antacid.
  • Chemical reaction: When one chemical substance is changed into a different one. How quickly a chemical reaction takes place can be affected by different factors, such as temperature.
  • Bicarbonate chemical reaction: When Alka-Seltzer tablets are dissolved in water, sodium bicarbonate splits apart to form bicarbonate (HCO3-) and this reacts with hydrogen (H+) from citric acid to form water and carbon dioxide gas (CO2). The bubbles you see are the carbon dioxide gas.

Materials

To do this activity you will need:

  • Alka-Seltzer tablets (2)
  • Jar, drinking glass, or vase with hot water (1)
  • Jar, drinking glass, or vase with ice-cold water (1)
  • Timer or clock that shows seconds (1)
  • Alternative: If you are doing the alternative version of this experiment, you will still use one jar with hot liquid and one jar with cold liquid, but the jars will have colored water and vegetable oil. You will also be given quartered, rather than whole, Alka-Seltzer tablet pieces.

Directions

  1. Do this activity with a partner. One person gets an Alka-Seltzer tablet ready and the other gets set to use the timer or clock to time how long it takes the tablet to dissolve completely in hot water.
Alka seltzer being dropped into water
Figure 1. One person should drop an Alka-Seltzer tablet in the jar while the other times how long it takes for the tablet to dissolve completely. Note: If you are doing the alternative version of the experiment your jars will contain colored water and vegetable oil— they will not look like this picture.
  1. The person with the timer counts to three. On three, the person with the tablet drops it into the jar with hot water and the other person starts timing. Note: If you are doing the alternative version of this experiment, using a jar with colored water and vegetable oil, the tablet piece may take a moment to sink down to the water. Start timing when the tablet reaches the water and starts reacting.
  2. The person who dropped the tablet should carefully watch the tablet dissolve in the jar. What happens as the tablet dissolves in the water?
  3. When the tablet has completely disappeared, the person watching it should say "Stop!" and the person timing should stop the timer (or note the seconds it took on the clock). How long did it take the tablet to disappear completely in the hot water? If instructed to do so, write the time in the data table.
Alka-Seltzer dissolving in water
Figure 2. Watch the jar until the tablet completely dissolves.

Condition Time Until Tablet Dissolved Completely
(sec)
Hot water  
Ice-cold water 
Table 1. If instructed to do so, write your results in a data table like this one. Record the time in seconds (sec).
  1. Now one person gets a second tablet ready and another person gets set to time how long it takes this tablet to dissolve in ice-cold water.
  2. Again, the person with the timer counts to three. On three, the person with the tablet drops it into the jar with ice-cold water and the other person starts timing. Note: If doing the alternative version, start timing when the tablet reaches the water and starts reacting.
  3. The person who dropped the tablet in the ice water should carefully watch the tablet dissolve. What happens as the tablet dissolves in the colder water? How different is it from how the tablet dissolved in the hot water?
  4. When the tablet has disappeared completely, the student watching it should say "Stop!" and the person timing should stop the timer (or note the seconds it took on the clock). How long did it take the tablet to dissolve completely in the ice-cold water?
  5. Did it take more or less time for the tablet to dissolve in the hot water compared to the ice water? Why do you think you got the results you did? Can you explain your results in terms of how the temperature affects the bicarbonate chemical reaction?