Question

The vapour pressure of two pure liquids, A and B that form an ideal solution are 300 and 800 torr respectively, at temperature T. A mixture of the vapour of A and B for which the mole fraction of A is 0.25 is slowly compressed at temperature T. Calculate (a) the composition of the first drop of the condensate.
Upto two decimal places and multiply the answer by 100.

Answer 1

$P{y}_A=P_A^o{x}_A$------------------------------(1)

$y_A=0.25$

$P_A^o=300torr$, $P_B^o=800torr$ ---------------------------(2)

$P=P_A^o{x}_A+P_B^o(1-x_A)$

Putting value of P from equation (1) in (2), we get

$1700\times x_A=800$

Hence, $x_A=0.47$