Potassium permanganate is prepared from the mineralpyrolusite, MnO_(2). Its crystals have deep purple colour. It acts as an oxidizing agent in the neutral, alkaline as well as acidicmedium. In acidicmedium , it is used in volumetric analysis for estimationof ferrous salts, oxalates etc. The titrations are carried out in presence of H_(2)SO_(4). However ,before using it as a titrant, it is first standized with standard oxalic acid solution or Mohr salt solution. In one of the experiments on titration , 13.4 g of dry pure sodium oxalate ( molar mass =134 g mol^(-1) ) was dissolvedin 100mLof distilled waterand then 100 mL of 2MH_(2)SO_(4) were added. The solution, was cooledto 25.30^(@) C. Now to this solution , 0.1 M KMnO_(4) solution was added till a very faint pink colour persisted. Mohr salt, FeSO_(4). (NH_(4))_(2) SO_(4). 6 H_(2)O is preferred over FeSO_(4). 7 H_(2)O for standardization of KMnO_(4) solution because.

Potassium permanganate is prepared from the mineralpyrolusite, MnO_(2)

1.	Potassium permanganate is prepared from the mineralpyrolusite, MnO_(2). Its crystals have deep purple colour. It acts as an oxidizing agent in the neutral, alkaline as well as acidicmedium. In acidicmedium , it is used in volumetric analysis for estimationof ferrous salts, oxalates etc. The titrations are carried out in presence of H_(2)SO_(4). However ,before using it as a titrant, it is first standized with standard oxalic acid solution or Mohr salt solution. In one of the experiments on titration , 13.4 g of dry pure sodium oxalate ( molar mass =134 g mol^(-1) ) was dissolvedin 100mLof distilled waterand then 100 mL of 2MH_(2)SO_(4) were added. The solution, was cooledto 25.30^(@) C. Now to this solution , 0.1 M KMnO_(4) solution was added till a very faint pink colour persisted. Mohr salt, FeSO_(4). (NH_(4))_(2) SO_(4). 6 H_(2)O is preferred over FeSO_(4). 7 H_(2)O for standardization of KMnO_(4) solution because.
Answer» Mohr salt is a DOUBLE salt while ferrous sulphate is a single salt. Mohr salt is not hygroscopic but `FeSO_(4).7 H_(2)O` is hygroscopic Mohr slat contains only ferrous ions whereas ferrous sulphate contains some ferric ions. Mohr salt solution can be titrated even in the absenceof `H_(2)SO_(4)` Solution :`FeSO_(4). 7H_(2)O` contains some ferric ions due to aerial OXIDATION.