(in moderately acidic solution)
|35.67 (Molar = 6 Normal)*|
(in strongly acidic solution)
|53.50 (Molar = 4 Normal)|
*Basis used for standardizing RICCA CHEMICAL COMPANY Potassium Iodate solutions
Potassium Iodate is an oxidizing agent and a good primary standard with the one drawback of having a relatively low equivalent weight. It is used primarily as a stable source of Iodine, which is liberated in the presence of Iodide ion and acid, in the titration of Thiosulfate and Sulfite solutions. The Iodide can be included in the Iodate solution or added before the acid is added and titration is begun. In solutions of moderate acidity (0.1 - 2.0 M HCl), the reactions involved are:
IO3- + 5 I- + 6 H+→ 3 I2 + 3 H2O
2 S2O32- + I2 → S4O62- + 2 I-
SO32- + I2 + H2O → SO42- + 2 I- + 2 H+
In this series of reactions, the equivalent weight of Potassium Iodate is one-sixth the molecular weight. RICCA CHEMICAL COMPANY Potassium Iodate and Potassium Iodate-Iodide titrants are intended for use in weakly acidic medium, and the normalities are calculated on this basis.
In stronger Hydrochloric Acid solutions, Iodate oxidizes the Iodine generated in the first reaction above to Iodine Monochloride, and the equivalent weight of Potassium Iodate is one-fourth the molecular weight.
Potassium Iodate can also be used as a basimetric standard for standardization of strong acids. A slight excess of both Potassium Iodate and Potassium Iodide is added, and the Iodine generated (see the first equation above) is then titrated with standard Sodium Thiosulfate using Starch indicator.