Question

A mixture of ethyl alcohol and propyl alcohol has vapour pressure of $290mm$ at $300K$. The vapour pressure of propyl alcohol is $200mm$. If mole fraction of ethyl alcohol is $0.6$ its vapour presssure at same temperature will be:-

• A. $360$
• B. $350$
• C. $300$
• D. $700$

Answer 1

Answer: (B)

$350$

as $P_{sol}=X_{sol}.P_{sol}^o$ $X\to$ mole fraction
$P^o\to$ pure vapour pressure of solution
$290mm=X_{ethanal}.P_{ethanal}^o+X_{propanal}.P_{propanal}^o$
$290mm=0.6\times P_{ethanal}^o+(1-0.6)\times 200mm$
on solving
$P_{ethanal}^o=350$ $nm$