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The vapour pressure of ethanol and methanol are 44.5 mm and 88.7 Hg respectively. An ideal solution is formed at the same temperature by mixing 60 g of ethanol with 40 g of methanol. Calculate the total vapour pressure of the solution and the mole fraction of methanol in the vapour.

The vapour pressure of ethanol and methanol are 44.5 mm and 88.7 Hg respectively. An ideal solution is formed at the same temperature by mixing 60 g of ethanol with 40 g of methanol. Calculate the total vapour pressure of the solution and the mole fraction of methanol in the vapour.

Grade:upto college level

3 Answers

Deepak Patra
askIITians Faculty 471 Points
10 years ago
Hello Student,
Please find the answer to your question
Ptotal = pA + pB
Molecular weight of CH3OH = 12 + 3 + 16 + 1 = 32
Molecular weight of C­2H5OH = 24 + 5 + 16 + 1 = 46
According to Raoult’s law
Ptotal = p1 + p2
Where Ptotal = Total vapour pressure of the solution
P1 = Partial vapour pressure of one component
P2 = Partial vapour pressure of other componenet
Again, p1 = Vapour pressure (po1) * mole fraction
Similarly, p2 = Vapour pressure (po2) * mole fraction
Mole fraction of CH3OH = 40/32 /40/32+60/46 = 0.49
Mole fraction of ethanol = 60/46 /60/46+40/32 = 0.51
NOTE THIS STEP : Thus now let us first calculate the partial vapour pressures, i.e., p1 and p2 of the two component.
Partial vapour pressure of CH3OH(p1)
= 44.5 * 0.51 = 22.69 mm
∴ Total vapour pressure of the solution
= 43.48 + 22.69 mm = 66.17 mm
Mole fraction of CH3OH in vapour = 43.48/66.17 = 0.65

Thanks
Deepak patra
askIITians Faculty
Sandeep
13 Points
6 years ago
P=P1+P2MOLECULAR WEIGHT OF CH3OH=32(p1)MOLECULAR WEIGHT OF C2H5OH=46(p2)NOW WE HAVEP1=vapour pressure(P`1)×mole fractionP2=vapour pressure (P`2)×mole fraction ThenMole fraction of CH3OH=0.49Mole fraction of C2H5OH=0.51P1=44.5×0.49=22.69P2=88.7×0.51=44.8P=P1+P2=66.9mm=total vapour pressure of the mixture 66.9mm Mole fraction of CH3OH in vapour is 44.8/66.17 = 0.65
Abhishat Tiwari
15 Points
5 years ago
The vapor pressure of pure water is 760 mm at 25.c the vapour pressure of solution ccontanning 1(m) solution. Of glucose will be 
 

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