Question

The molarity of `NaNO_(3)` solution is 1 M. The density of solution is 1.25 g/ml. Calculate molality of solution. (Molar-Mass of `NaNO_(3)=85 g`).

Answer 1

1 M means that 1 mole of `NaNO_(3)` (i.e. 85 g) is present in 1000 ml of solution.
Mass of solution = Volume of solution `xx` density
`= 1000 xx 1.25 = 1250 g`
Mass of solvent = Mass of solution - Mass of solute
`= 1250 - 85`
= 1165 g
Molality (m) `=("Number of moles of solute")/("Mass of solvent (in kg)")`
`=(1)/(1165//1000)=(1000)/(1165)`
`= 0.858 m`