Question

The density of 2.0 M solution of a solute is `1.2 g mL^(-1)`. If the molecular mass of the solute is `100 g mol^(-1)`, then the molality of the solution is
A. 2.0 m
B. 1.2 m
C. 1.0 m
D. 0.6 m

Answer 1

Correct Answer - A
2 M solution has 2 moles of solute dissolved in one litre (1000 mL) of the solution
Mass of the solution `= V xx d = 1000 mL xx 1.2 "g mL"^(-1) = 1200 g`
Mass of solvent `= (1200 - 200)g = 1000g = 1kg`
Molality of solution (m) `= ("No. of moles of solute")/("Mass of solvent in Kg")`
`("2 mol")/("1 kg")=2 "mol Kg"^(-1)=2`m.