Question

What is the molality of aqueous solution of urea having mole fraction of solute 0.03?

Answer 1

1. Molarity of water = 55.5 M

55.5 moles is present in 1 L of water.

2. So,

$$\begin{gathered} {\chi }_{urea}=\frac{n_{urea}}{n_{urea}+n_{water}} \\ 0.03=\frac{n_{urea}}{n_{urea}+55.5} \\ {n}_{urea}=1.71 \end{gathered}$$

​3. Molality = $\frac{n_{urea}}{Massofsolventinkg}=\frac{1.71}{1kg}=1.71molal$