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Q.
Mole fraction of a solute in benzene is $0.2$ then find molality of solute:
Bihar CECEBihar CECE 2004Solutions
Solution:
Let molality of solution $=x$
$\therefore $ Moles of solute in $1000 \,g$ 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 $0.2 x+2.564=x$
$2.564=x-0.2 x$
$x=\frac{2.564}{0.8}=3.2$