Question

A solution is prepared by urea and water. If mole fraction of water is 0.8 in the solution. Find the ratio of mass of water and urea.

• A. $\frac{5}{6}$
• B. $\frac{6}{5}$
• C. $\frac{1}{4}$
• D. $\frac{4}{1}$

Answer 1

Answer: (B)

$\frac{6}{5}$

Let $x_1$ and $x_2$ be the mole fraction of water and urea respectively.

Therefore, $x_1+x_2=1$ and $x_1=0.8$. Hence, $x_2=0.2$.

$\frac{x_1}{x_2}=\frac{W_1\times M_2}{W_2\times M_1}$

W and M are weight and molar mass.

$M_1=18g.{mol}^{-1}$

$M_2=60.0g.{mol}^{-1}$

Therefore, $\frac{W_1}{W_2}=\frac{0.8\times 18}{0.2\times 60}$

$\frac{W_1}{W_2}=\frac{6}{5}$

Hence the correct option is B.