Question

In an aqueous solution mole fraction of water is 0.75. The molality of the solution is:

• A. $1.85m$
• B. $18.5m$
• C. $1m$
• D. $2.75m$

Answer 1

Answer: (B)

$18.5m$

Mole fraction of $H_{2}O$ in solution $=0.75$

$\therefore$ Mole fraction of solute in solution $=1-0.75=0.25$

Hence each mole of solution, $0.25$ mole of solute is dissolved.

$0.75$ mole of water $=18\times 0.75=13.5gm=0.0135Kg$

Molality $\left(m\right)=$ no. of moles of solute / mass of solvent

$=\frac{0.25}{0.0135}=18.5m$

$\therefore$ Correct answer is $B$.