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

Mohr's salt is FeSO4.NH42SO4.6H2Oonly  oxidisable  part  Fe2+  isFe2+→  Fe3++e− ×  6 Cr2O72−  +  14H+ + 6e− →  2Cr3+ +7H2O6Fe2+  + Cr2O72−  +  14H+ →6 Fe3++2Cr3+  +  7H2OMillimoles  of  Fe2+ =M1V1= 750  ×  0.6=450Moles of  Fe2+ = 4501000  =  0.450  mol6  mol  Fe2+ ≡  1  mol  Cr2O72−∴    0.450  mol  Fe2+ ≡  0.4506 =  0.075  mol  Cr2O72−                        =0.075  ×   294  g=22.05  g