Part A If 0.740 mol of a nonvolatile nonelectrolyte are dissolved in 3.50 mol of
ID: 878305 • Letter: P
Question
Part A
If 0.740 mol of a nonvolatile nonelectrolyte are dissolved in 3.50 mol of water, what is the vapor pressure PH2O of the resulting solution? The vapor pressure of pure water is 23.8 torr at 25 C .
Express your answer with the appropriate units.
19.6 torr
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For solutions that contain solutes that dissociate, the number of moles of particles produced must be taken into consideration in determining the mole fraction of the solvent. For solutions that contain solutes that are volatile, the vapor pressure of the solution will be determined by both the solvent and the solutes.
Solutions containing volatile solutes
In solutions composed of two liquids (A and B), each liquid contributes to the total vapor pressure above the solution. The total vapor pressure is the sum of the partial pressures of the components:
Ptotal=PA+PB=XAPA+XBPB
where PA and PB are the vapor pressures of pure A and B, respectively.
Part B
A solution is composed of 1.60 mol cyclohexane (Pcy=97.6 torr) and 2.20 mol acetone (Pac=229.5 torr). What is the total vapor pressure Ptotal above this solution?
Express your answer with the appropriate units.
174 torr
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If a third volatile component had been present in this solution, the total pressure would be calculated in a similar manner but would involve three terms rather than two. For example,
Ptotal=PA+PB+PC=XAPA+XBPB+XCPC
Part C
As you saw in Part B, the vapor above the cyclohexane-acetone solution is composed of both cyclohexane vapor and acetone vapor. What mole fraction of the vapor above the solution, Xcy(vapor), is cyclohexane?
PH2O =19.6 torr
Explanation / Answer
Answer –
We are given moles of cyclohexane = 1.60
Moles of acetone = 2.20 moles
So total moles = 1.60 + 2.20 = 3.8 moles
We know, mole fraction = mole / total moles
Mole fraction cyclohexane =1.60 mole / 3.8 mole
= 0.421