Question

Vapour pressure of chloroform (CHCl₃) and dichloromethane (CH₂Cl₂) at 298 K are 200 mm Hg and 415 mm Irrespectively, (i) Calculate the vapour pressure of the solution prepared by mixing.25- 5 g of CHCl₃ and 40 gof CH₂Cl₂ at 298 K and (ii) mole fractions of each component in vapour phase.

Answer 1

Let CH₂Cl₂ = A

CHCl₃ = B

Molar mass of A,

M_a = 12 × 1 + 1 × 2 + 2 × 35.5

= 85 g mol^-1

Molar mass of B,

MB = 12 × 1 + 1 × 1 + 3 × 35-5

= 119.5 g mol^-1

Mass of A,

W_A = 40 g Mass of B,

W_B = 25.5 g

Vapour pressure of A,

p°_A = 415 mm of Hg

Vapour pressure of B,

p°<subB = 200 mm of Hg

x_B = 1 – x_A

= 1 – 0.688

= 0.31

p = p_A + P<subB

= p°_A x_A + p°_B x_B

= 415 × o.688 + 200 × 0.312

= 285.52 + 62.4

= 347.92 mm of Hg

Mole fraction of components in gas phase,

PA = y_A.p

p°_A x_A = y_A.P

415 × 0.688 = y_A × 347.92

y_A = 285⋅52347⋅92 = 0.82

= 1 – 0.82

= 0.18