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,
$m=\frac{x_B\times 1000}{\left(1-x_B\right)\times m_A}\dots \left(i\right)$
where, $x_B$= mole fraction of solute
$m_A$ = molar mass of solvent
$0.8=\frac{x_B\times 1000}{\left(1-x_B\right)\times 18}$
$x_B=0.014$
Let $w_B=xg,w_A=100g$
$m=\frac{w_B\times 1000}{60\times w_A}$
$0.8=\frac{x\times 1000}{60\times 100}$
$x=4.8\%$