1g of NaCl is dissolved in 10g of a solution the density of which is 1.07g//"cc". Find the molality and molarity of NaCl.

1g of NaCl is dissolved in 10g of a solution the density of which is 1

1.	1g of NaCl is dissolved in 10g of a solution the density of which is 1.07g//"cc". Find the molality and molarity of NaCl.
Answer» Solution :(i) LET us consider one litre of sodium thiosulphate solution `:.` WT of the solution `=` DENSITY `xx` volume (mL) `=1.25xx1000=1250g` Wt. of `Na_(2)S_(2)O_(3)` present in 1L of the solution `=` molarity `xx` mol.wt. `=3xx158=474g` Wt `%` of `Na_(2)S_(2)O_(3)=(474)/(1250)xx100=37.92%` (ii) Wt. of solute `(Na_(2)S_(2)O_(3)=474g` Moles of solute `=(474)/(158)=3` Wt. of solvent `(H_(2)O)=1250-474=776g` Moles of solvent `=(776)/(18)=43.11` `:.` mole fraction of `Na_(2)S_(2)O_(3)=(3)/(3+43.11)=0.063` (iii) MOLALITY of `Na_(2)S_(2)O_(3)=("moles of " Na_(2)S_(2)O_(3))/("wt.of solvent in grams")xx1000` `=(3)/(776)xx1000=3.865m` `:.1` mole of `Na_(2)S_(2)O_(3)` contains 2 moles of `NA^(+)` ions and 1 mole of `S_(2)O_(3)^(2-)` ions `:.` molality of `Na^(+)=2xx3.865=7.73m` Molality of `S_(2)O_(3)^(2-)=3.865m`