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)

Let molality of solution $=x$
$\therefore$ Moles of solute in $1000g$ benzene
$=\frac{1000}{78}=12.82$
Mole fraction of solute $=\frac{x}{x+12.82}$
Given mole fraction of solute $=0.2$
$\therefore 0.2=\frac{x}{x+12.82}$
or $0.2(x+12.82)=x$
or $0.2x+2.564=x$
$2.564=x-0.2x$
$x=\frac{2.564}{0.8}=3.2$