Question

The density of a 3 M sodium thiosulphate solution (Na₂S₂O₃) is 1.25 g per mL. 

Calculate

(i) the percentage by weight of sodium thiosulphate

(ii) the mole fraction of sodium thiosulphate and

(iii) the molalities of Na+ and S₂O₃^2- ions.

Answer 1

Given, molarity of Na₂S₂O₃ = 3 mol/L 

:. Moles of Na₂S₂O₃ = 3

Thus, weight of Na₂S₂O₃  = 3 x 158 = 474 g

and volume ( V) of solution = 1 L = 1000 mL 

.'. Weight of solvent = 1250 - 474 = 776 g