Question

Mole fraction of a solute in benzene is $0.2$ then find molality of solute:

• A. 3.2
• B. 2
• C. 4
• D. 3.6

Answer 1

Answer: (A)

3.2

Answer 2

Let the solution be $x$ molal then moles of solute present in $1000\, g$ of benzene $=\frac{1000}{78}=12.82$ moles. $\therefore$ Mole fraction of solute $=\frac{x}{x+12.82}$ $0.2=\frac{x}{x+12.82}$ $0.2(x+12.82) =x$ $0.2 x+2.564 =x$ $2.564 =x-0.2 x$ $=0.8 x$ $x=\frac{2.564}{0.8}=3.2$