10 g of a mixture of sodium chloride and anhydrous sodium sulphate is dissolved in water. An excess of barium chloride solution is added and 6.99 g. of barium sulphate is precipitated according to the equation :-
Na2SO4+BaCl2⟶BaSO4+2NaCl
Molecular weight of BaSO4=137+32+64=233
Molecular weight of Na2SO4=2∗23+32+64=142
233gof BaSO4 is obtained from 142g of Na2SO4
6.99g of BaSO4 will be obtained from 142233×6.99 = 4.26g of Na2SO4
Percentage of Na2SO4 in 10g of mixture = 4.2610×100= 42.6%