Question

A solution is prepared by mixing 2.88 mol of acetone with 1.45 mol of cyclohexane at 30°C. 2nd attempt 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: 2,88 mol ÷ (2,88 mol + 1,45 mol) = 0,665.
cyclohexane: 1,45 ÷ (2,88 mol + 1,45 mol) = 0,335.
Raoult's Law: 
P(total) = P(acetone) · χ(acetone)  + P(cyclohexane) · χ(cyclohexane).
P(total) = 229,5 torr · 0,665 + 97,6 torr · 0,335.
P(total) = 185,3 torr.
χ for acetone: 229,5 torr · 0,665 ÷ 185,3 torr = 0,823.
χ for cyclohexane:  97,6 torr · 0,335 ÷ 185,3 torr = 0,177.