100 ml of 0.1 N hypo decolourised iodine by the addition of x g of crystalline copper sulphate to excess of KI. The value of ‘x’ is (molecular wt. of CuSO4. 5H2O  is 250)

Cu+2SO41mole+2KI→K2SO4 +Cu+2I2 ;       2CuI2+2 →  CuI2+1 + I2I2+Na2S2O31mole→  2NaI  + Na2S4O6Eq.  wt.  of  CuSO4.5H2O =Mol.  wtchange in oxidation state of 'Cu'=2501=250100  ml  of  0.1  N hypo ≡  100  ml  of 0.1  N  CuSO4.  5H2Omass of  CuSO4.5H2O=N×E×V1000=250  ×  0.1 ×   1001000 = 2.5  g