Determination of the oxalate ion concentration using 0.02M potassium permanganate

Theory-

Permanganate is the general name for a chemical compound containing the manganate(VII) ion.Thus manganese in the +7 oxidation state, the manganate (VII) ion is a strong oxidizer.In an acidic solution, manganate (VII)is reduced to the colorless +2 oxidation state of the manganate(II) ion.

• In a strongly acidic medium,

• In a weak acidic or neutral medium,

• In an alkaline medium,

Since the manganate (VII) ion is violet and the manganate (II) ion is nearly colorless, the end point can be taken as the first permanent pink color appears in the solution.

In a basic solution, manganate (VII) is either reduced to the brown +4 oxidation state of manganese dioxide or to the green +6 oxidation state of manganate ion.

Permanganate solutions are unstable.Therefore it is not a primary standard.So permanganate solutions must be standardized before using for titrations.Oxalate can be used as a primary standard to standardize permanganate.

Initially the reaction is slow but later the reaction is catalyzed by formed manganate (II) ions,so becomes more rapid.

Permanganate also can be standardize with arsenic (III) oxide.

The reaction of arsenic (III) ions with permanganate ions take place without complication in acidic medium if a trace of an iodine compound (eg: Potassium iodate ) is added as a catalyst.This reaction generally carry out in HCl rather than sulfuric acid.

Permanganate titrations with,

• Hydrogen peroxide in acidic medium.


• iron (II) ion in acidic medium.

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