Question

The vapour pressures of two volatile liquids A and B at 25°C are 50 Torr and 100 Torr, respectively. If the liquid mixture contains 0.3 molar fraction of A, then the mole fraction of liquid B in the vapour phase is `x/17`. The value of x is ______.

Answer 1

The vapour pressures of two volatile liquids A and B at 25°C are 50 Torr and 100 Torr, respectively. If the liquid mixture contains 0.3 molar fraction of A, then the mole fraction of liquid B in the vapour phase is `x/17`. The value of x is 14.

Explanation:

Given: `p_A^circ = 50` Torr

`p_B^circ = 100` Torr

x_A = 0.3 ⇒ x_B = 0.7

`P_"Total" = P_A^circ x_A + P_B^circ x_B`

= 50 × 0.3 + 100 × 0.7

= 15 + 70

= 85 torr

partial pressure of B:

`p_B = p_B^circx_B`

= 100 × 0.7

= 70 Torr

`y_B = p_B/p_"Total"`

= `70/85`

= `14/17`

∴ x = 14; y = 17