Chlorine The Bacteria Killer

Biology, Chemistry:	Microorganisms, Chlorine-Based Cleaners
Grade Range:	Elementary School, Middle School
Format:	Hands-on

This is your basic yeast demonstration with an addition of bleach. This demonstration is simple to set up and easy for kids to understand, but you will want towels in case there is a spill.

Materials

• 6 Test Tubes
• Test Tube Stand
• Balloons
• Yeast
• Sugar
• Water
• Hot Plate
• 600mL Beaker
• Bleach

Safety Precautions

Please read the General Safety Precautions section of the Demonstration Safety page before performing this demonstration.

Demonstration

1. Prepare the test tubes: Put a small amount of yeast in each test tube along with some sugar in each. In three of the test tubes, fill them 1/4 of the way with bleach. Add water into each test tube, filling them about 2/3 of the way, and put a balloon on each test tube. Set them all in the beaker, fill the beaker 2/3 with water, and set it on the hot plate on a low setting.
2. As students come to visit your table and as the test tubes warm, the yeast will wake up and start to consume the sugar, releasing CO₂ and filling the balloons. Once a few balloons are noticeably filled with air, set all the test tubes in the test tube stand.
3. After explaining that there is yeast in each of the test tubes, ask students for ideas on why some of them aren't producing CO₂. Discuss and explain.

Why This Works

Yeast is a Microorganism, a tiny living creature that can't easily be seen without a microscope. Yeast is a fungus that is often used in baking, since it eats sugars and produces CO₂, which makes dough rise for bread and other baked goods. In order for yeast to do this, they need to be in a wet, warm environment such as these test tubes of warm water. Since the yeast are inside these test tubes with warm water and sugar, they are able to eat the sugar and produce CO₂, which fills the balloons over the tops of the test tubes.

Some of the balloons are not inflating, even though they also have the warm water and sugar. This is because they have an extra "ingredient" added: chlorine bleach. Chlorine is an element that, when mixed with water, produces hydrochloric acid, a powerful acid that is used in low concentrations as a house cleaner. This is because it can destroy microorganisms such as yeast, and make it hard for future microbes to live on the surface. Anti-Microbial Cleaners are useful in making sure surfaces are clean, and destroying micoorganisms that could make people sick. This is why it is important to wash our hands and clean tables or counters before preparing food and eating at them, so to minimize the risk for illness.

Additional Information

• This demonstration is shown another way in the Life on Mars demonstration.