By Veronica I. Jaramillo
- Ask an adult for permission to do the activity and for help when necessary.
- Read all directions and safety recommendations before starting the activity.
- Wear appropriate personal protective equipment (safety glasses, at a minimum), including during preparation and clean up.
- Tie back long hair and secure loose clothing, such as long sleeves and drawstrings.
- Do not eat or drink food when conducting this activity.
- Clean up and dispose of materials properly when you are finished with the activity.
- Thoroughly wash hands after conducting the activity.
- Caution: hot liquids!
- Do not eat or drink any of the materials used in this activity.
Disposal: All liquids and solutions can be poured down the drain with running water. Solid waste can be disposed of in the trash.
Introduction of activity
Alka-Seltzer is a common antacid used to relieve an upset stomach. Alka-Seltzer and other fizzing tablets produce carbon dioxide-filled bubbles when placed in water. As the carbon dioxide is produced, you can see bubbles grow and float to the surface of the water. You may even be able to hear the bubbles as they pop.
Let’s see how you can make the fizzing reaction of Alka-Seltzer tablets go faster or slower. We can monitor the formation of carbon dioxide by hearing the fizz and seeing how long it is produced.
- 6 Alka-Seltzer Gold tablets
- Room temperature water, 125 mL
- Cold tap water, 125 mL (about ½ cup)
- Hot tap water, 125 mL
- Vinegar, 375 mL (about 1½ cups)
- 6 clear plastic or glass cups or Ziplock bags
- Stopwatch or stopwatch app that can measure seconds
- Measuring cup ½ cup (250 mL)
- 1 piece of scrap paper (wax or parchment paper works too)
Prepare for the activity
- Pour 125 mL (about ½ cup) of vinegar into each of 3 clear cups or bags. Vinegar simulates the excess acid in the stomach.
- Unwrap 3 packets of Alka-Seltzer tablets so that there are 6 tablets.
- Fold one piece of scrap, wax, or parchment paper in half.
Part 1. How does the tablet surface area affect how fast or slow the reaction will occur?
- As you start the stopwatch, drop one Alka-Seltzer tablet in the first cup of vinegar.
- Stop the time when the bubbling ends and record this time in the chart.
- Place an Alka-Seltzer tablet between the pages of a piece of folded paper near the crease. Use the bottom of the measuring cup to press on the tablet and break it into about 6-8 pieces.
- As you start the stopwatch, slide the Alka-Seltzer tablet pieces down the crease of the paper into the second cup of vinegar.
- Stop the time when the bubbling ends.
- Using the same piece of folded paper, place an Alka-Seltzer tablet inside the pages near the crease. Use the bottom of the measuring cup to press and crush the tablet into a fine powder.
- As you start the stopwatch, slide the powdered Alka-Seltzer down the crease of the paper into the third cup of vinegar.
- Stop the time when the bubbling ends.
Part 2. How does temperature affect how fast or slow the reaction will occur?
- Add 125 mL (approximately ½ cup) of hot tap water to the first clean clear cup, 125 mL of room temperature water to the second clean cup, and 125 mL of cold water in the third clean cup. Use an oven mitt or potholder when handling the hot tap water.
- As you start the stopwatch, place one whole Alka-Seltzer tablet into each of the three cups of water.
- Compare the amount of bubbling in each cup. Write the time the bubbling ends in each cup in the chart.
Part 1. Surface Area data table
Describe what you heard and saw. How vigorous was the bubbling?
Part 2. Temperature data table
Room Temperature water
- From your observations in Part 1, what change to the surface area made the reaction go faster?
- From your observations in Part 2, how did the temperature change affect how fast the reaction occurred?
How does it work?
Alka-Seltzer reacts with an acid to make carbon dioxide gas. When you added the tablet to the vinegar or water, you heard fizzing and saw bubbling. If the reaction is going faster, then it will take less time to finish and will fizz more vigorously.
The speed of a reaction depends on the number of collisions between molecules. The carbon dioxide forms when two key ingredients in these tablets, citric acid and baking soda (sodium bicarbonate), dissolve in water and then randomly collide into each other in just the right way. The sodium bicarbonate must collide with the acid to make the carbon dioxide gas. When surface area is increased, the citric acid and sodium bicarbonate dissolve better and faster in water. When these dissolved particles collide, the chemical reaction happens. More dissolved particles leads to more collisions and a faster reaction. In your trials, when was the surface area the largest? Did the rate go faster?
Temperature also affects the rate of a reaction. When temperature is increased, molecules move faster, so it is likely there will be more collisions in the same amount of time. Think about a class of students entering a room. If they walk, there is less chance that they will bump into another student, but if all the students are running into the room it is very likely there will be some collisions between students. In your trials, did the hot or cold water finish first?
Using what you learned about changing the rate of chemical reaction, what would you do if you wanted to make the reaction with Alka-Seltzer happen even faster than your fastest recorded time? What could you try if you wanted to make it happen slower than your slowest recorded time?
Veronica I. Jaramillo, Ph.D. is the Natural Science Department Cair at Pasadena City College.
Alka Seltzer® is a registered trademark of Bayer HealthCare LLC.