Question

The hardness of a water sample containing 10 ^–3 M MgSO₄ expressed as CaCO₃ equivalents (in ppm) is ______. 

(molar mass of MgSO₄ is 120.37 g/mol)

Answer 1

MgSO₄10^-3mol/lit = 10^-3mol/lit of CaCO₃

Hardness is ppm = 10^-3 x 100g x 1000(mg/g)

= 100mg/lit = (100 x 10^-3)/1000

= 100ppm

Answer 2

1 Litre has 10^–3 moles MgSO₄ 

So , 1000 litre has 1 mole MgSO₄ 

= 1 mole CaCO₃ = 100 ppm