Titrimetric Determination of Nitrites

Nitrites are oxidised in acid solutions by permanganate which is reduced to Mn(Il), the permanganate acts as a self indicator. Due to the volatility of HNO2 (formed in acidified solutions of nitrite) and their oxidation in air, nitrite cannot be directly titrated against permanganate. It is more appropriate to add an aliquot of the nitrite solution beneath the surface to a known excess of permanganate, back titrating the excess with a standard reductant e.g. iron(Il) solution. 

Weigh out accurately 1 g purest potassium nitrite, dissolve in boiled-out water and make up to 250 cm in a volumetric flask. Deliver from a burette 30.0 cm of standardised 0.02 M permanganate solution into a 600 cm beaker. Add 30 cm of 1 5 v/v of sulphuric acid solution and dilute to about 300 cm. Heat the beaker to 40 C and add slowly, while stirring magnetically, 25.0 cm of the freshly prepared nitrite solution, which is placed in a burette. Ensure that the tip of the burette is below the surface of the 

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