Bones, shells and certain rocks; such as limestone, calcite and chalk contain a compound called calcium carbonate. When calcium carbonate comes in contact with acid, it reacts by bubbling and foaming. Environmentalists have discovered that acid rain -- which is rain water that is slightly acidic -- can erode these rocks over time.
You will need to gather a few materials: about 20 milliliters of 15 percent diluted sulfuric acid solution, a bucket of water, rubber gloves, an eye dropper, safety goggles and a piece of limestone. Put on safety goggles and rubber gloves to protect yourself from accidentally coming into contact with the sulfuric acid. Using an eye dropper, drip several drops of acid onto the limestone rock. The acid will react with carbonate ions in the limestone, and it will foam. The parts of the limestone that receive the acid will be dissolved and form a new substance, calcium acetate. When done, rinse your limestone rock in the bucket of water to further dilute any residual acid on the rock.
Expand your project, by testing other forms of acid on your limestone rock. For example, vinegar and lemon juice are acidic, although they are weak acids. Vinegar contains acetic acid, and lemon juice contains citric acid. Experiment with the juice of other citric fruits, also.
Do some research on what causes acid rain. Collect rain water and use litmus paper to determine the pH of rain in your town.