2 2 7 Perform A First Hand Investigation To Demonstrate The

Method 1:
- Using a straw, five breaths were exhaled into limewater. The limewater turned cloudy, indicating that exhaled air contained carbon dioxide.
- 10 mL of water was added to a test tube
- Universal indicator was added to the water, and the colour of the solution noted
- Using a straw, five breaths were exhaled into the water
- Colour change of the solution was recorded
- Steps 4-5 were repeated 5 more times, adding 5 more exhalations each time.

- As number of breaths increased, the pH of the water decreased. Since exhalations contain carbon dioxide, it can be concluded that dissolved carbon dioxide decreases the pH of water.

Independent Variable: the number of breaths of carbon dioxide
Dependent Variable: the pH of the water

Method 2:
- 20 mL water was added to each of two conical flasks
- A delivery tube from a third flask was inserted into one of the conical flasks with water
- A few chips of calcium carbonate CaCO3 and 20 mL of hydrochloric acid were added to this third flask, and it was stoppered.
- After 1 minute, universal indicator was added to the two flasks with water in them, and colours noted.

- Hydrochloric acid and CaCO3 react to form carbon dioxide, which dissolved in water to lower the pH of the water.