The mass of potassium dichromate crystals required to oxidise 750 cm3 of 0.6 M Mohr's salt solution is (Given, molar mass : potassium dichromate = 294, Mohr's salt = 392)

Mohr's salt is FeSO4·NH42SO4·6H2OOnly oxidisable part isFe2+Fe2+⟶Fe3++e-×6Cr2O72-+14H++6e-⟶2Cr3++7H2O6Fe2++Cr2O72-+14H+⟶6Fe3++2Cr3++7H2O Millimoles of Fe2+=750×0.6=450 Moles of Fe2+=4501000=0.450 mol6 moles of Fe2+≡1 molCr2O72-∴0.450 mole Fe2+≡0.4506=0.075 mol Cr2O72-= 0.075 x 294 g= 22.05 g