Acidification Experiments Note: To prepare “seawater,” dissolve 35 grams of salt per liter of tap water. Mix well.
Part I: Carbon Dioxide in Seawater
Materials: beaker seawater
small rubber hose
carbon dioxide bubbler (or dry ice as a substitute) universal pH indicator
Procedure:
This experiment tests the hypothesis that carbon dioxide (CO2) added to seawater increases its acidity. 1. Fill the beaker about three-quarters full of seawater.
2. Add the universal indicator to the seawater and use the key to test the starting pH of the seawater. The pH of seawater varies, depending on location and other factors. Record your starting pH on the board.
3. Place one end of the small rubber hose on the CO2 bubbler and dip the other end into the seawater.
(Note: If you are using dry ice as a substitute, place it in a beaker with a cover/tube assembly that allows you to capture the gas as the dry ice melts. If necessary, place the beaker in a pan of warm water to increase the rate of melting.)
4. Allow the CO2 to bubble into the seawater, then shut off the bubbler and test the pH again. Record the new pH.
Does CO2 change the pH of seawater? How?
Part II: Chalk in Acid Materials: beaker
hydrochloric acid chalk
pH indicator
Note: Hydrochloric acid is highly caustic. Do not touch with hands. Do not handle except with caution. This is not recommended as a student experiment.
1. Pour a small amount of hydrochloric acid into a beaker. 2. Test its pH as described in the first experiment.
3. Drop a piece of chalk into the acid and observe the results, as the chalk instantly dissolves.