Which of the following statements are true for Mohr’s salt?
It decolorizes KMnO4 solution
It is a double salt
It is a primary standard substance
Mohr's salt or ammonium ferrous sulphate is the inorganic compound with the formula (NH4)2Fe(SO4)2.6H2O containing two different cations Fe2+and NH+4. It is classified as a double salt of ferrous sulphate and ammonium sulphate.
It is a standard laboratory reagent. Like the other ferrous sulphale salts, ferrous ammonium sulphate dissolves in water to give the aquo complex which has octahedral molecular geometry. Mohr's salt has a molar mass of 392.21 g/mol and it appears as a blue green solid.
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 for titration of KMnO4
In the titration with KMnO4 , the MnO−4 ion is reduced to Mn2+ in the presence of acid and Fe2+ ions of Mohr’s salt is oxidized to Fe3+ .