JEE Main · 2021 · 16 Mar 2021 · Shift 2 · Solutions

At 363 K, the vapour pressure of

A

is 21 kPa and that of

B

is 18 kPa. One mole of

A

and 2 moles of

B

are mixed. Assuming that this solution is ideal, the vapour pressure of the mixture is _____ kPa. (Round off to the nearest integer).

Answer: 19

Solution

In an ideal solution each component obeys Raoult's law and the total vapour pressure is the sum of the two partial pressures. The mole fractions are

x_{A} = \frac{1}{3}

and

x_{B} = \frac{2}{3}

, so

p = p_{A}^{\circ} x_{A} + p_{B}^{\circ} x_{B} = 21 \times \frac{1}{3} + 18 \times \frac{2}{3} = 7 + 12

The vapour pressure of the mixture is 19 kPa.

JEE Main · 2021 · 16 Mar 2021 · Shift 2 · Integer answer

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