Solutions and Colligative Properties 1 Question 25
24. The vapour pressure of ethanol and methanol are 44.5 and $88.7 \mathrm{~mm} \mathrm{Hg}$ respectively. An ideal solution is formed at the
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Solution:
- Moles of ethanol $=\frac{60}{46}=1.3$
Moles of methanol $=\frac{40}{32}=1.25$
$\Rightarrow$ Mole fraction of ethanol $=\frac{1.3}{1.3+1.25}=0.51$
$\Rightarrow$ Vapour pressure of solution $=p_{\text {ethanol }}+p_{\text {methanol }}$ $=0.51 \times 44.5+0.49 \times 88.7$
$$ =66.16 \mathrm{~mm} $$
Mole fraction of methanol in vapour phase
$$ \begin{aligned} & =\frac{p_{\text {methanol }}}{\text { Total vapour pressure }} \ & =\frac{43.463}{66.16}=0.657 \end{aligned} $$
