Potassium Dichromate

Potassium Dichromate
Chemical Formula K2Cr2O7
Formula Weight 294.18
Equivalent Weight 49.03 (Molar = 6 Normal)
CAS No. 7778-50-9

Potassium Dichromate is a versatile, powerful oxidizing agent (although not as powerful as Potassium Permanganate) that also meets the requirements of being a primary standard. Potassium Dichromate is commonly used in acid solution to standardize Ferrous salt solutions using Ferroin indicator:

Cr2O72- + 6 Fe2+ + 14 H+ → 2 Cr3+ + 6 Fe3+ + 7 H2O

Potassium Dichromate is also used to standardize Sodium Thiosulfate solutions. In acidic solution, Potassium Dichromate oxidizes Potassium Iodide to Iodine; the Iodine thus generated can then be titrated with the Thiosulfate solution using Starch Indicator:

Cr2O72- + 6 I- + 14 H+ → 2 Cr3+ + 3 I2 + 7 H2O

Hexavalent Chromium compounds (the form present in the Dichromate ion) are carcinogenic, and this fact should be considered when evaluating Potassium Dichromate against other oxidizers such as Ceric Sulfate, Potassium Iodate and Potassium Permanganate.