When acids react with bases, the final pH will vary. Have students add a squirt of bromthymol blue, phenolphthalein and alizarin to separate test tubes. Add 4 drops of 0.1M HCl to each. Neutralize the acid by adding 3 or 4 drops of 0.1M NaOH to the bromthymol blue until it turns green or just barely turns blue. Counting the drops of base, repeat the process with phenolphthalein until a light pink color appears and with alizarin until a purple appears.
Indicators change colors at various pH values.
It should take more base for the second two and this gives an indication of the higher pH at which they change color. Finally three titrations are done in the normal fashion. Everyone will use 10 mL of acid but some groups should use 0.1M hydrochloric acid, others 0.1M sulfuric acid and the rest 0.1M phosphoric acid. Investigation of the number of H's in the formula of the acid should give the clue. Two H's will neutralize twice the volume of base and three H's three times.