The hardness of water sample containing 0.002 mole of magnesium sulphate dissolved in a litre of water is expressed as

The hardness of water sample containing 0.002 mole of MgSO4 dissolved in 1 L of water.Hardness is measured in terms of ppm of CaCO3MgSO4≡CaCO3≡ 0.002 mol L-1 CaCO3= 0.002 x 100 gL-1              =0.002×100g in 103mL=0.002×100×106103g in 106mL(ppm)=200 ppm