Question

A solution is composed of 1.50 mol cyclohexane (P∘cy=97.6 torr) and 2.70 mol acetone (P∘ac=229.5 torr). What is the total vapor pressure Ptotal above this solution?

As you saw in Part B, the vapor above the cyclohexane-acetone solution is composed of both cyclohexane vapor and acetone vapor. What mole fraction of the vapor above the solution, Xcy(vapor), is cyclohexane?

Answer 1

total pressure   = Xcy* P⁰ cy    + Xac *P⁰ ac

no of moles of cyclohexane   ncy   = 1.5moles

no of moles of actone         nac        = 2.7

mole fraction of cyclohexane Xcy = ncy/ncy + n ac

                                                         = 1.5/1.5 + 2.7

                                                          = 1.5/4.2   = 0.357

mole fraction of acetone Xac           = nac/ncy + n ac

                                                         = 2.7/1.5 + 2.7

                                                          = 2.7/4.2    = 0.643

total pressure   = Xcy* P⁰ cy    + Xac *P⁰ ac

                         = 0.357*97.6+ 0.643*229.5

                         = 182.4 torr >>>>>answer

part-B

no of moles of cyclohexane   ncy   = 1.5moles

no of moles of actone         nac        = 2.7

mole fraction of cyclohexane Xcy = ncy/ncy + n ac

                                                         = 1.5/1.5 + 2.7

                                                          = 1.5/4.2   = 0.357