Question

A 5 M aqueous solution of ethanol has a density of 1.025 g/mL. Find its molality

• A. 5.12 m
• B. 6.29 m
• C. 6.69 m
• D. 4.85 m

Answer 1

The correct option is B 6.29 m

5 M ethanol $\Rightarrow$ 5 moles (5 mol $\times$46 g/mol) of solute in 1000 mL solution
$\Rightarrow$Mass of solution $=$volume $\times$density
$1000\times 1.025=1025g$
$\Rightarrow$Mass of solvent =1025-(5$\times$46)=795 g
$\Rightarrow Molality=\frac{\text{no. of moles of solute}}{\text{Mass of solvent in kg}}=\frac{5\times 1000}{795}=6.29m$