Yeast is a tiny living fungus that can be used in a simple school project to make a balloon inflate. When yeast is mixed with warm water and sugar, it becomes active and starts using the sugar for energy. As it feeds, it releases carbon dioxide gas, which fills the balloon on top of the bottle.
This experiment helps students see that some chemical changes can make a gas.
Key Facts
- Yeast + sugar + warm water can produce carbon dioxide gas.
- Carbon dioxide gas is written as CO2.
- Fermentation word equation: sugar -> carbon dioxide + alcohol + energy.
- A common glucose fermentation equation is C6H12O6 -> 2CO2 + 2C2H5OH + energy.
- Warm water helps yeast become active, but hot water can kill it.
- More carbon dioxide in the bottle means a larger balloon, if the setup is sealed well.
Vocabulary
- Yeast
- Yeast is a tiny living fungus that uses sugar for energy and can produce carbon dioxide gas.
- Carbon dioxide
- Carbon dioxide is a colorless gas, CO2, that can inflate a balloon when enough of it is produced.
- Fermentation
- Fermentation is a process in which yeast breaks down sugar without needing oxygen.
- Variable
- A variable is one part of an experiment that can be changed or measured, such as water temperature or amount of sugar.
- Control
- A control is a comparison setup that helps show whether the tested change caused the result.
Common Mistakes to Avoid
- Using water that is too hot, because high heat can kill the yeast and stop carbon dioxide production.
- Forgetting to seal the balloon tightly on the bottle, because gas can leak out instead of inflating the balloon.
- Changing several things at once, because using different sugar amounts, water temperatures, and yeast amounts together makes the results hard to explain.
- Expecting instant results, because yeast needs time, often 30 to 60 minutes, to produce enough carbon dioxide to noticeably inflate a balloon.
Practice Questions
- 1 A group tests 4 bottles with the same amount of yeast and water. Bottle A has 0 teaspoons of sugar, Bottle B has 1 teaspoon, Bottle C has 2 teaspoons, and Bottle D has 4 teaspoons. If sugar is the food source, which bottle would you predict inflates the balloon the most, and why?
- 2 A balloon has a circumference of 6 cm at the start and 18 cm after 45 minutes. How many centimeters did the balloon circumference increase?
- 3 Two bottles have the same yeast and sugar. One uses warm water and the other uses ice-cold water. Explain which balloon should inflate faster and connect your answer to yeast activity and fermentation.