Solutions and Colligative Properties - Result Question 25
####24. The vapour pressure of ethanol and methanol are 44.5 and $88.7 mm Hg$ respectively. An ideal solution is formed at the
Topic 2 Colligative Properties
Objective Questions I (Only one correct option)
Show Answer
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 $=p _{\text {ethanol }}+p _{\text {methanol }}$ $=0.51 \times 44.5+0.49 \times 88.7$
$$ =66.16 mm $$
Mole fraction of methanol in vapour phase
$$ \begin{aligned} & =\frac{p _{\text {methanol }}}{\text { Total vapour pressure }} \ & =\frac{43.463}{66.16}=0.657 \end{aligned} $$
