Question

The density of 3 molal sodium thiosulphate is 1.25 g/cm³. The mole fraction of sodium thiosulphate is

Answer 1

(i) Mass of 1000 mL of Na2S2O3 solution = 1.25×1000=1250g

Mass of Na2S2O3 in 1000 mL of 3 M solution

=3×MolmassofNa2S2O3

=3×158=474g

Mass percentage of Na2S2O3 in solution

=1250474×100=37.92

Alternatively, M=mAx×d×10

3=158x×1.25×10

x=37.92

(ii) No. of moles of Na2S2O3=158474=3

Mass of water =(1250−474)=776g

No. of moles of water =18776=43.1

Mole fraction of Na2