Potassium Bromate is a powerful oxidizing agent in acid solution and is a convenient, stable source for Bromine. When Bromide ion is also present (either already in the Bromate solution, as in Bromate-Bromide solutions, or added to the sample before the titration is begun) and the solution is acidified, Bromine is produced according to the following reaction:
BrO3- + 5 Br- + 6 H+ → 3 Br2 + 3 H2O
The endpoint can be detected by using a pH indicator, such as Methyl Red or Methyl Orange, that is destroyed by the first excess of Bromine and thus changes color irreversibly from its normal color in acid solution to colorless. Starch indicator can also be used in oxidation titrations using Bromate, if Iodide ion is added instead of Bromide ion, as shown in the following reaction:
BrO3- + 6 I- + 6 H+ → Br- + 3 I2 + 3 H2O