Question

The density of 3m solution of na2s2o3 is 1.58g ml calculate mole fraction of na2s2o3

Answer 1

Density of solution =1.25g/ml

Mass of solution = 1000×1.25=1250g

Molarity of solution = 3M

Mass of 3 moles of solute (Na2S2O3)=3×158g/mol=474g

Mass of solvent =1250g−474g=776g

Na2S2O3↔2Na++S2O2−3

1 mole of Na2S2O3 will furnish 6 mole of Na+ and 3 mole of S2O2−3

Mass of 1 mole of Na+=23.11g/mol

Mass of 6 mole of Na+=6×23=138g

Mass of 1 mole of S2O2−3=112g/mol

Mass of 3 mole of S2O2−3=3×112=336g

Molality of Na+=(mass of Na+×1000)/Molecular mass of Na+× Mass of solvent )

Molality of Na+=(138×1000)/(23×776)=7.73m

Molality of S2O3=(mass of S2O3×1000)/Molecular mass of S2O2−3× Mass of solvent )

Molality of Na+=(336×1000)/(112×776)=3.86m