This method is official in major pharmacopoeias and is widely used for its accuracy and simplicity in pharmaceutical analysis.
The assay of hydrogen peroxide (H2O2) is typically performed using redox titration with a standardized solution of potassium permanganate (KMnO4) in an acidic medium.
Principle– The principle behind this method is the oxidation-reduction reaction between the hydrogen peroxide (the reducing agent) and the potassium permanganate (the oxidizing agent).Hydrogen peroxide is an oxidising agent because it can easily liberate oxygen but when it is titrated against acidic medium KMnO4,it has been act as reducing agent.
The Chemical Reaction
The reaction is carried out in the presence of dilute sulfuric acid (H2SO4).
The balanced chemical equation
2KMnO4+5H2O2+4H2SO4→2MnSO4+5O2+K2SO4+8H2O
In this reaction:
- The permanganate ion (MnO4−), in which manganese has an oxidation state of +7, is reduced to the manganese ion (Mn2+), with an oxidation state of +2. This causes a color change from purple to a colorless solution.
- The hydrogen peroxide (H2O2) is oxidized to oxygen gas (O2) and water.
The Titration Process
The titration is performed by adding the potassium permanganate solution from a burette to a known volume of the hydrogen peroxide sample in a conical flask. Since the potassium permanganate solution is intensely purple, it acts as its own indicator. The endpoint of the titration is reached when the first drop of potassium permanganate solution turns the mixture a faint, persistent pink color, indicating that all the hydrogen peroxide has reacted and the permanganate is now in excess.
The assay of hydrogen peroxide (H₂O₂) using potassium permanganate (KMnO₄) as a titrant is a standard method outlined in the Indian Pharmacopoeia (IP). The reaction is monitored until the endpoint, indicated by the persistence of a pink color due to excess KMnO4.
PROCEDURE-
Take 10 ml of sample solution in a 250 ml of volumetric flask and add purified water upto the mark. From this solution take 25 ml of solution in a conical flask and add 5N Sulphuric acid and titrate it against 0.1 N Potassium permanganate solution until faint pink colour was obtained.
Each ml of 1N KMnO4 is equivalent to 0.01701 gm of H2O2
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