When testing for chlorides, what is the indicator used?

The indicator used for testing chlorides is potassium chromate. This compound works effectively in determining the presence of chlorides through a titration method. When performing a titration, potassium chromate acts as an indicator in the reaction with silver nitrate, which is used to precipitate chloride ions as silver chloride. Upon the complete reaction of chlorides, the addition of an excess of silver nitrate will cause the solution to turn a yellow color, indicating the presence of silver chromate and signaling that all chloride ions have reacted.

Using potassium chromate is particularly effective because it provides a clear and distinct visual change that marks the end point of the titration process, making it easier for the operator to determine the concentration of chlorides in the water sample being tested. The other indicators listed do not serve the same specific purpose in chloride testing. Sodium thiosulfate is typically used in redox titrations, bromothymol blue is a pH indicator, and phenolphthalein is also a pH indicator, none of which are suitable for detecting chloride levels in the same way potassium chromate is.