Question

8 g of NaOH is dissolved in 18 g of $H_{2}O$. Find the mole fraction and molality (mol $k{g}^{-1})$ of NaOH in the resultant solution.

• A. 0.2, 11.11
• B. 0.167, 11.11
• C. 0.167, 22.2
• D. 0.2, 22.2

Answer 1

The correct option is B 0.167, 11.11

Number of moles of NaOH $n_{NaOH}=\frac{8}{40}=0.2$ mol
Number of moles of $H_{2}O$ in 18 g of $H_{2}O,n_{H_{2}O}=\frac{18}{18}=1$ mol
Mole fraction, ${\chi }_{NaOH}=\frac{n_{NaOH}}{n_{NaOH}+n_{H_{2}O}}$
$\therefore {\chi }_{NaOH}=\frac{0.2}{1+0.2}=\frac{0.2}{1.2}=0.167$
$\text{Molality}=\frac{\text{Number of moles of soliute}}{\text{Mass of solvent in kg}}$
$\text{Molality}=\frac{0.2\times 1000}{18}=11.11m$