Solutions containing volatile solutes where P ?A and P ?B are the vapor pressure

Question

Solutions containing volatile solutes

where P?A and P?B are the vapor pressures of pure A and B, respectively.

If 0.720mol of a nonvolatile nonelectrolyte are dissolved in 3.60mol of water, what is the vapor pressure PH2o of the resulting solution? The vapor pressure of pure water is 23.8 torr at 25 degree C. Ptotal=PA+PB=XAPA degree +XBPB degree Whewre PA degree and PB degree are the vapor pressures of pure A and B respectively. A solution is composed of 1.80mol cyclohexane (P degree cy= 97.6 torr) and 2.00mol acetone ( P degree ac. = 229.5 torr). What is the total vapor pressure Ptotai above this solution? Express your answer with the appropriate units.

Explanation / Answer

part A):

According to Raoult's law when non -volatile solute dissolved in solvent then

Po -Ps/Po= mole fraction of solute

Po-------------> prue solvent vapour pressure = 23.8 torr

Ps----------------> solution vapour pressure =?

mole fraction = 0.720/(0.720+3.6) = 0.167

23.8-Ps/23.8 = 0.167

Ps = 19.82

solution vapour pressure = Ps = 19.82 torr

part B)

Ptotal = mole fraction of Cy x partial pressure pf Cy+ mole fraction of acetone x partial pressure of acetone

         = (1.8/1.8+2) x 97.6 + (2/1.8+2) x229.5

         = 46.23 + 120.78

          =167 torr

total pressure = 167 torr

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