Urban Ecology

CO2 Tester

What it does

This experiment shows you how to make a limewater solution to test for carbon dioxide, and a couple of ways you can use it.

What you need

For limewater:

• One tablespoon of lime (the kind used to make pickles)
• 2 quart-sized glass jars with lids

For tests:

• Pint-sized glass jar
• Drinking straw
• Soda bottle
• Small drinking glass
• 1 teaspoon sugar
• 1/2 package of powdered yeast
• About 18 inches of aquarium tubing
• Modeling clay

What to do

Part I:

1. Fill a one-quart jar with water.
2. Add one tablespoon of lime and mix thoroughly.
3. Cover the jar and let the solution stand overnight.
4. The following day, pour the clear liquid from the top into the second quart-size jar. Be careful not to pour the lime that has settled to the bottom of the first jar.
5. Keep the second jar, closed, for use in experiments.

What it's all about

The clear liquid is a saturated solution of limewater. At first, the mixture looks milky white because the undissolved particles were suspended in the water. These particles eventually sank to the bottom. The solution must be kept covered to prevent carbon dioxide in the air from dissolving in it.

Part II:

1. Fill the pint-sized jar half full of limewater.
2. Using the straw, exhale into the limewater (blow bubbles).
3. Continue to exhale until you see the limewater change color.

What it's all about

A chemical in the limewater mixes with the carbon dioxide in your breath to form a white powder that cannot be dissolved in water. The powder, limestone, turns the water milky white. Eventually, the limestone powder will sink to the bottom of the jar.

Part III:

1. Pour 1/2 package of yeast into the soda bottle.
2. Fill the bottle halfway with warm water.
3. Add one teaspoon of sugar to the bottle.
4. Cover the bottle with your thumb and shake it up to mix the contents.
5. Insert one end of the aquarium tubing into the top of the bottle and seal it there with clay. Be sure the clay seals off the bottle completely except for where the tube comes through.
6. Put the free end of the tube into a glass that is half-full of limewater.
7. Watch what happens, and observe over the course of several days.

What it's all about

There will be some foaming in the soda bottle, and bubbles will flow out of the tube into the limewater. The limewater will turn milky white. Yeast is a plant that uses sugar and oxygen to produce energy. When it produces energy it gives off carbon dioxide, like all plants. This carbon dioxide comes out through the tube into the limewater, turning the limewater cloudy. Over time, the white limestone particles will sink to the bottom of the glass.

Remember, be sure you have a parent, teacher, or other adult help you!

 

 

See how ASU scientists are studying carbon dioxide in the Phoenix area.
Read about it.