Answer to Question #166835 in Physical Chemistry for Fiza Shaikh

Question

A water sample contains Ca(HCO3)2=32.4 mg/l, Mg(HCO3)2=29.2mg/l, CaSO4=13.6 mg/l. Calculate the temporary,permanent and total hardness of water sample

Answer 1

Hardness is expressed in terms of CaCO3.

0.001 mole MgSO4 means 0.12 grams or 120 mg of MgSO4 dissolved in 1 litre of solution.

Assuming density of water to be unity, 1000 ml = 1000g

1000g H20 contains = 120mg of MgSO4.

=> 10^6 g H20 = 120g MgSO4.

Now, to calculate hardness :-

1 mole MgSO4 = 1 mole CaCO3.

=> 120g MgSO4 = 100g CaCO3.

This molar mass is equal to the calculated mass of MgSO4.

Thus, hardness of water will be 100 ppm