Question

Why 2N h2so4 solution is added in a titration between kmno4 and feso4 .7h2o

Answer 1

Mohr’s salt is a double salt of ferrous sulphate and ammonium sulphate and its composition is FeSO4.(NH4)2SO4.6H2O.

Simplest reason for using sulphuric acid in the preparation of a standard solution of Mohr’s salt in redox titration is to prevent hydrolysis of the Fe2+ ions.

Ferrous ions of Mohr’s salt undergo hydrolysis in aqueous solution. To prevent the hydrolysis, Conc. H2SO4 needs to be added to the Mohr’s salt crystals during the preparation of its standard solution.

Another reason is also to prevent the oxidation of Fe2+ ions of Mohr’s salt to Fe3+ ions. As this titration is generally carried out with KMnO4 or K2Cr2O7 and both are good oxidising agents.

Note : HCl or HNO3 cannot be used as HNO3 is also a very good oxidising agent and if we use HCl, Cl- of HCl will be oxidised by KMNo4 or K2Cr2O7 to chlorine gas.

HAPPY LEARNING!!