Theory
In an acid-base titration, the important information to obtain is the equivalence point. If there are a given number of moles of acid in the titration flask, the equivalence point is reached when that same number of moles of base have been added from the buret. The molarity of the base can then be calculated since the number of moles of base added is the same as the number of moles of acid in the flask, and the volume of the base added is also known. Similarly, if the number of moles of acid in the titration flask is unknown, it can be calculated for the equivalence point if the molarity of the base and the volume of base added are known.
Often the pH of the solution will change dramatically at the equivalence point. An acid-base indicator works by changing color over a given pH range. If an indicator which changes color near the equivalence point is chosen, there is also a dramatic change in the color of the indicator at the equivalence point because the pH changes so rapidly.
In a potentiometric acid-base titration, an indicator is not necessary. A pH meter is used to measure the pH as base is added in small increments (called aliquots) to an acid solution. A graph is then made with pH along the vertical axis and volume of base added along the horizontal axis. From this graph the equivalence point can be determined and the molarity of the base calculated.
