JEE Main 2023 · Chemistry · Solutions, Solid State and Surface Chemistry · easy

Liquids A and B form an ideal solution. Their vapour pressures in the pure state at a given temperature are 80 and 60 torr respectively. A solution…

Single correct option

Liquids A and B form an ideal solution. Their vapour pressures in the pure state at a given temperature are

80

and

60\ \mathrm{torr}

respectively. A solution is made from

2\ \mathrm{mol}

of A and

3\ \mathrm{mol}

of B. The mole fraction of A in the vapour in equilibrium with this solution is

Show answer and solution

Answer: (B) $0.47$

Liquid mole fractions:

x_A=0.4

x_B=0.6

. Partial pressures (Raoult):

p_A=0.4\times80=32

torr,

p_B=0.6\times60=36

torr. Total

=68

torr. Dalton:

y_A=p_A/p_{\mathrm{total}}=32/68=0.47

. The vapour is richer in the more volatile component A than the liquid (

0.40

), so the answer must exceed

0.40

;

0.40

is the liquid composition, not the vapour composition.

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