An ideal solution was obtained by mixing methanol and ethanol. If the partial vapour pressure of methanol and ethanol are `2.619 kPa` and `4.556 kPa`, respectively, the composition of vapour (in terms of mole fraction) will be

Options

A. 0.635 methanol, 0.365 ethanol
B. 0.635 methanol, 0.365 ethanol
C. 0.574 methanol, 0.326 ethanol
D. 0.173 methanol, 0.827 ethanol

Answer

B

Explanation

Method I : Trick
Ratio should be same of pressures and mole fractions which tally from option (b) i.e., 1 : 2.
Method II : Calculation
Partial pressure of methanol = 2.619 kPa .
Partial pressure of ethanol = 4.556 kPa .
Total pressure = partial pressure of methanol + partial pressure of ethanol
= 2.619 + 4.556 = 7.175 kPa
`chi_("methanol")=("Partial pressure of methanol")/("Total pressure")`
`=(2.619kPa)/(7.175kPa)=0.365`
`chi_("ethanol")=(4.556kPa)/(7.175kPa)=0.634`