Question

The vapor pressure of ethanol (CH3CH2OH) at 20c is 44 mm Hg, and the vapor pressure of Methanol (CH3OH) at the same temperature is 94 mm Hg. A mixture of 30.0 g of Methanol and 45.0 g ethanol is prepared and can be assumed to behave ideally. Anwser the following questions concerning this mixture.​

A) Which component is more volatile?

A2) Determine the mole fraction of both components of the liquid mixture?

B) Calculate the vapor pressure of methanol and ethanol above the solution.

P ethanol=      P Methanol=

C) Calculate the total vapor pressure?

P total=

D) What is the mole fraction of each component in the vapor phase?

Xethanol=? XMethanol?

E) What method can be used to seperate the 2 components from one another? Specifically describe how the ethanol and methanol will be seperated by this method? Be sure to address which component would be collected and which one would be left behind.

F) Sketch a simple apparatus that could be used to seperate this mixture with the method described above.

Answer 1

a) The component which is having more vapor pressure at the given conditinos is more volatile. Hence methanol is more volatile than ethanol.

Molecular weights : Methanol (CH3OH)=32 Ethanol (CH3CH2OH)=46

Mass of methanol =30 gm moles of methanol= 30/32=0.9375 Moles of ethanol=45/46= 0.9783

total moles = Moles of methanol + moles of ethanol = 0.9375+0.9783=1.9158

Mole fractions : Methanol 0.9375/1.9158 =0.489 and ethanol= 1-0.489= 0.511

b)Vapor pressures above the solutions, methanol =0.489* pure component vapor pressure= 0.489*94=46 mmHg and that of ethanol= 0.511* pure component vapor pressure =0.511*44=22.484 mm Hg

v)Total pressure = partial pressure of ethanol in the vapor space + Partial pressure of methanol in the vapor space= 44+22.484= 66.484 mm Hg

d)Mole fractions in vapor phase: Methanol= Partial pressure/ Total pressure = 46/66.484=0.692 and ethanol =1-0.692= 0.308

e) Relative volatility = 94/44 ( vapor pressur of methanol)/ Vapor pressure of methanol) = 2.13. Hence distillation can be used for separating the components since relative volatility is high. Vacuum distillation is good chioce.

f) top component will be richer in methanol and bottom will be richer in ethanol

sketch