Question

Molality of a solution in aqueous medium is $0.8$. Calculate its mole fraction and the percentage by mass of solute if molar mass of solute is $60$

• A. $4.5\%$
• B. $4.6\%$
• C. $4.7\%$
• D. $4.8\%$

Answer 1

Answer: (D)

We know that,
$m=\frac{x_{B}\times1000}{\left(1-x_{B}\right)\times m_{A}} \ldots\left(i\right)$
where, $x_{B}$= mole fraction of solute
$m_{A}$ = molar mass of solvent
$0.8=\frac{x_{B}\times1000}{\left(1-x_{B}\right)\times18}$
$x_{B}=0.014$
Let $w_{B}=x\,g, w_{A}=100\,g$
$m=\frac{w_{B}\times1000}{60\times w_{A}}$
$0.8=\frac{x\times1000}{60\times100}$
$x=4.8\%$