The density of 3 M solution of sodium thiosulphate `(Na_(2)S_(2)O_(3))` is 1.25 g/mL. Calculate
molality of `Na^(+) " and "S_(2)O_(3)""^(2-)`ions

Explanation

Molarity of `Na_(2)S_(2)O_(3)`
`" "=("moles of "Na_(2)S_(2)O_(3))/"wt. of solvent in grams" times 1000`
`=3/776 times 1000=3.865`
`therefore` 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.
`therefore` molarity of `Na^(+)=2 times 3.865=7.73m`
Molarity of `S_(2)O_(3)^(2-)=3.865m`