REDUCTION OF ACID POTASSIUM PERMANGANATE BY IODIDE, NITRITE AND EROMIDE

Acid potassium permanganate may be quantitatively reduced to Mn2+ by iodide or nitrite when conditions are suitable (N/\(Io\) to 5N-H2SO4); 5-o and 2.5 moles of \(KI\) and KNO2 respecti7ely are required per mole of KMnO4. On the other hand, redaction by KBr (N/\(Io\) to 2N-H2SO4) stops short at the MnO2 stage. The complete reduction to Mn2+ may perhaps be attained at 2 to 3N-H2SO4 but further increase in acid concentration (up to 8N) leads to evolution of oxygen and the consumption of KBr again drops steadily In the \(KI\) titration of KMnO4, there is an initial inflection at 0.5 mole \(KI\) and in the KNO2 titration, at 1.5 moles, but each of these shifts to larger amounts as the sulphuric acid concentration in the mixture is increased