Redox Chemistry Problem?

Question

Calculte the purity of a sample of iron II ammonium sulfate (FeSO4 (NH4)2 SO4, 6H2O0. A quantity of 7.5g of it was dissolved in acid solution and then completely oxidised by 25mL of 0.12M pottassium dichromate (K2Cr2O7).

Answer 1

In a redox reaction, FeSO4 (NH4)2 SO4, 6H2O gives up 1 electron, while K2Cr2O7 acquires six (two Cr(IV) being reduced to Cr(III))

So M(K2Cr2O7) x V (L)(K2Cr2O7) x 6 = moles electrons transferred = mol Fe2+

Now you can work out what actual mass of FeSO4 (NH4)2 SO4, 6H2O you had.  Divide that by 7.5 g, and you will have your answer.