Alka-Seltzer Science: The Effect of Temperature on Reaction Time
Have you ever wondered why bubbles form when an Alka-Seltzer tablet is put in water? If you’ve ever tried it, you’ve seen that the tablet fizzes furiously when dropped into water. The moment the tablet starts dissolving, a chemical reaction occurs that releases carbon dioxide gas. This is what the bubbles are. Some factors can change how quickly the carbon dioxide gas is made, and consequently affect how furiously the tablet fizzes. In this activity you’ll explore whether you can make an Alka-Seltzer tablet fizz faster or slower by changing the temperature of the water. How does the water’s temperature affect the reaction?
This activity is not appropriate for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.
Alka-Seltzer is a medical drug that works as a pain reliever and an antacid (antacids help neutralize stomach acidity, such as heartburn). The pain reliever used is aspirin and the antacid used is baking soda, or sodium bicarbonate. To take the tablets, they’re fully dissolved in water, where they famously undergo a chemical reaction that produces lots of carbon dioxide bubbles. Why is this? As the tablets dissolve, the sodium bicarbonate splits apart to form sodium and bicarbonate ions. The bicarbonate ions react with hydrogen ions (from citric acid, another ingredient in the tablets) to form carbon dioxide gas (and water). This is how the bubbles are made.
How is temperature related to this reaction? For the reaction to occur, the bicarbonate ions must come into contact with the hydrogen ions in just the right way. The probability of the bicarbonate and hydrogen ions doing this is affected by temperature: the higher the temperature, the faster the molecules move; the lower the temperature, the slower they move. (The temperature of a solution is a measure of the average motion and energy of the molecules in the solution.)
Extra: Test Alka-Seltzer tablets in a wider range of temperatures, and then graph the time it takes a tablet to dissolve in water at each temperature (check with a thermometer). What temperature change is required to increase the reaction time by a factor of two? What about decreasing the reaction time by a factor of two?
Extra: Compare whole Alka-Seltzer tablets to pieces of Alka-Seltzer tablets. If there is a greater surface area (i.e., a tablet is broken up into more pieces), does the same amount of tablet result in the reaction happening faster or slower?
Extra: You could turn this activity into a homemade lava lamp! To do this, you will want to use a tall jar or empty clear plastic 1-liter or 2-liter bottle, fill it with about 2 inches of water, add 5 drops of food coloring, and then fill it at least three-quarters full with vegetable oil. You could repeat this activity using your homemade lava lamp at a cold and hot temperature. (You’ll need to devise a safe way to heat or cool each container.) You will also want to use one-quarter of an Alka-Seltzer tablet at a time (instead of a whole tablet). How does the bicarbonate reaction look in the homemade lava lamp?
Observations and Results
Did the Alka-Seltzer tablet dissolve much faster in the hot jar compared to the cold one? Were there a lot more bubbles produced initially in the hot water compared to in the cold water?
When the Alka-Seltzer tablet was added to the hot water, the tablet should have quickly dissolved, taking around 20 to 30 seconds to do so, depending on the exact temperature. When the tablet was added to the ice-cold water, it should have taken much longer to dissolve, with most of the tablet dissolving after about two to three minutes, but with some bubbles (from the tablet’s remains) still apparent after six minutes or longer. In the hot water, the tablet should have more vigorously produced bubbles than in the cold water. The higher the temperature, the faster the molecules move, and the more likely it is that the bicarbonate will contact hydrogen in just the right way for the chemical reaction to occur and produce carbon dioxide bubbles.
More to Explore
Teisha Rowland, PhD, Science Buddies
Science Buddies |
Chemical reactions, carbonation, temperature
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