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
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Answer:
Correct Answer: 24. $(0.657)$
Solution:
Moles of ethanol $=\dfrac{60}{46}=1.3$
Moles of methanol $=\dfrac{40}{32}=1.25$
$\Rightarrow$ Mole fraction of ethanol $=\dfrac{1.3}{1.3+1.25}=0.51$
$\Rightarrow$ 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} & =\dfrac{p _{\text {methanol }}}{\text { Total vapour pressure }} \\ & =\dfrac{43.463}{66.16}=0.657 \end{aligned} $
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