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Materials

The materials required for this experiment:

Procedure

For this experiment, the independent variable is the concentration of the carbon dioxide- which differs between the concentration of CO2 in the air expelled from our lungs versus the concentration of CO2 contained in the smoke from a car exhaust. The dependent variable is the level of acidity in the water. This is determined by measuring using a pH paper. The constants (control variables) are the type of water used (i.e. tap water, sea water etc), the amount of water and the time air is forced/blown into the water.
The water bottle is filled with 1 liter of tap water.
Take a pH reading of the water. Record the result in the table below.
Insert one end of the 300mm of rubber hose into the water in the bottle. Blow air through the tube and observe air bubbles rising from the tube through the water. Continue blowing for 3 minutes.

At the 3 minute mark, take a pH reading of the water. Record the result in the table below.

The water in the bottle is replaced with new tap water.
Fit a plastic bag around the exhaust pipe of a car. Fit it so that if air was to be expelled from the exhaust pipe, the bag would inflate. Secure the bag around the exhaust pipe with masking tape.
Make a small hole at the other end of the plastic bag and insert the 1 meter hose to a depth of about 5 cm. Secure the hose with masking tape.
Insert the free end of the hose into the water in the bottle. Start the car and watch the bag inflate and observe air bubbles rising from the tube through the water. Allow the bubbles to rish through the water for 3 minutes.
At the 3 minute mark, take a pH reading of the water. Record the result in the table below.
The human lung has about 4% carbon dioxide whereas the smoke from the car exhaust will have about 12% carbon dioxide.