
Concept explainers
(a)
Interpretation:
The mole fraction of 2-methylpentane and cyclohexane in liquid phase has to be given.
Concept Introduction:
Mole fraction: Mole fraction of a substance in a solution is the number of moles of that substance divided by the total number of moles of all substances present. The formula is,
(a)

Answer to Problem 12.86QE
The mole fraction of cyclohexane is
The mole fraction of 2-methylpentane is
Explanation of Solution
Given,
Weight of cyclohexane =
Weight of 2-methylpentane =
Vapor pressure of cyclohexane =
Vapor pressure of 2-methylpentane =
The moles of 2-methylpentane and cyclohexane are calculated from their molar masses.
Moles of cyclohexane=
Moles of 2-methylpentane=
The mole fraction of cyclohexane in the liquid phase is calculated as,
Mole fraction of cyclohexane=
Mole fraction of cyclohexane=
Mole fraction of cyclohexane=
The mole fraction of 2-methylpentane is calculated from the mole fraction of cyclohexane.
Mole fraction of 2-methylpentane=
Mole fraction of 2-methylpentane=
The mole fraction of cyclohexane is
The mole fraction of 2-methylpentane is
(b)
Interpretation:
The vapor pressures of cyclohexane and 2-methylpentane above the solution have to be given.
Concept Introduction:
The equilibrium between a liquid and its vapor produces a characteristic vapor pressure for each substance that depends on the temperature. The lowering of the vapor pressure is caused by a lesser ability of the solvent to evaporate, so equilibrium is reached with a smaller concentration of the solvent in the gas phase. The vapor pressure of a solution is expressed using Raoult’s law:
The vapor pressure of the solvent
(b)

Answer to Problem 12.86QE
The vapor pressure of cyclohexane is
The vapor pressure of 2-methylpentane is
Explanation of Solution
Given,
Weight of cyclohexane =
Weight of 2-methylpentane =
Vapor pressure of cyclohexane =
Vapor pressure of 2-methylpentane =
The moles of cyclohexane are calculated from its molar mass.
Moles of cyclohexane=
The mole fraction of cyclohexane in the liquid phase is calculated as,
Mole fraction of cyclohexane=
Mole fraction of cyclohexane=
Mole fraction of cyclohexane=
The vapor pressure of cyclohexane is given as,
Vapor pressure of cyclohexane=
Vapor pressure of cyclohexane=
Vapor pressure of cyclohexane=
The moles of 2-methylpentane are calculated from its molar mass.
Moles of 2-methylpentane=
The mole fraction of 2-methylpentane is calculated from the mole fraction of cyclohexane.
Mole fraction of 2-methylpentane=
Mole fraction of 2-methylpentane=
The vapor pressure of 2-methylpentane is given as,
Vapor pressure of 2-methylpentane=
Vapor pressure of 2-methylpentane=
Vapor pressure of 2-methylpentane=
The vapor pressure of cyclohexane is
The vapor pressure of 2-methylpentane is
(c)
Interpretation:
The mole fraction of 2-methylpentane and cyclohexane in vapor phase has to be given.
Concept Introduction:
Refer to part (a) and (b).
(c)

Answer to Problem 12.86QE
The mole fraction of cyclohexane in vapor phase is
The mole fraction of 2-methylpentane in vapor phase is
Explanation of Solution
The vapor pressure of cyclohexane is
The vapor pressure of 2-methylpentane is
The total vapor pressure is
The mole fraction of cyclohexane and 2-methylpentane are calculated as,
Mole fraction=
Mole fraction of cyclohexane=
Mole fraction of 2-methylpentane=
The mole fraction of cyclohexane in vapor pressure is
The mole fraction of 2-methylpentane in vapor pressure is
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Chapter 12 Solutions
Chemistry Principles And Practice
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