Question

A solution is prepared by mixing 3.44 mol of acetone with 1.45 mol of cyclohexane at 30°c. calculate the χacetone and χcyclohexane in the vapor above the solution. p°acetone = 229.5 torr and p°cyclohexane = 97.6 torr.

Answer 1

First calculate the mole fraction of each substance:
acetone: 3.44 mol ÷ (3.44 mol + 1.45 mol) = 0.703
cyclohexane: 1.45 ÷ (3.44 mol + 1.45 mol) = 0.297
Raoult's Law: P(total) = P(acetone) · χ(acetone)  + P(cyclohexane) · χ(cyclohexane)
P(total) = 229.5 torr · 0.703 + 97.6 torr · 0.297
P(total) = 190.3 torr
χ for acetone: 229.5 torr · 0.703 ÷ 190.3 torr = .848
χ for cyclohexane:  97.6 torr · 0.297 ÷ 190.3 torr = .152