Potassium Permanganate

Potassium Permanganate
Chemical Formula KMnO4
Formula Weight 158.03
Equivalent Weight 31.61 (Molar = 5 Normal)
CAS No. 7722-64-7

Potassium Permanganate is a versatile and powerful oxidant that can be used to determine many substances by direct or indirect titration. A unique advantage of Potassium Permanganate is that it serves as its own indicator. Titrations with Permanganate must be carried out in strong acid solution. Sulfuric Acid is generally used for this purpose because Nitric Acid and Hydrochloric Acid can participate in competing oxidation-reduction reactions, reducing the accuracy of the titration.

Potassium Permanganate is not considered a primary standard substance and solutions of it are usually standardized with Arsenic Trioxide or Sodium Oxalate, both of which are available from the National Institute of Standards and Technology (NIST). RICCA CHEMICAL COMPANY uses the latter in standardizing our Potassium Permanganate titrants. The reactions involved with both standards are:

2 MnO4- + 5 H3AsO3 + 6 H+ → 2 Mn2+ + 5 H3AsO4 + 3 H2O

MnO4- + 5 H2C2O4 + 6 H+ → 2 Mn2+ + 10 CO2 + 8 H2O

The Arsenious Acid in the first reaction is produced by neutralization of the alkaline solution used to dissolve the Arsenic Trioxide. The Oxalic Acid in the second equation is formed when the Sodium Oxalate is dissolved in the acid solution before the titration is begun. Since the Manganese is reduced from the +7 to the +2 (Manganous) state, the equivalent weight of Potassium Permanganate is one-fifth its molecular weight.

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