Forwards and Backwards: pH and Indicators

Visitors prepare six solutions combining vinegar and ammonia that range incrementally from acid (all vinegar) to base (all ammonia). They add an indicator to each solution and compare the resulting colors to those on a pH scale chart. Visitors then use a flask containing water and indicator solution. They add drops of ammonia and vinegar, experimenting with the number of drops it takes to change the color of the water (indicating pH) from acid to base and back again. Visitors learn about pH and the pH scale, and about acid and base solutions. They learn that they can test for pH with an indicator solution. They also learn that some chemical reactions are reversible.