As the concentration of a solution increases, its vapor pressure decreases. For
ID: 861776 • Letter: A
Question
As the concentration of a solution increases, its vapor pressure decreases. For a nonvolatile solute B in a liquid solvent A, the relationship between concentration and vapor pressure is expressed by Raoult's law: PA=XAP?A where PA is the vapor pressure of the solution, XA is the mole fraction of solvent, and P?A is the vapor pressure of the pure solvent. In a two-component solution consisting of A and B, the mole fraction, X, of component A is defined as XA=moles Amoles A + moles B.Part A If 0.340mol of a nonvolatile nonelectrolyte are dissolved in 3.90mol 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. PH2O = SubmitHintsMy AnswersGive UpReview Part 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=XAP?A+XBP?B where P?A and P?B are the vapor pressures of pure A and B, respectively. Part B A solution is composed of 1.50mol cyclohexane (P?cy=97.6 torr) and 2.50mol acetone (P?ac=229.5 torr). What is the total vapor pressure Ptotal above this solution? Express your answer with the appropriate units. Ptotal = SubmitHintsMy AnswersGive UpReview Part Part C This question will be shown after you complete previous question(s).
Explanation / Answer
Part A
Total moles = moles of non electrolyte + moles of water = 0.34 + 3.90 = 4.24
Mole fraction of water = 3.90/4.24 = 0.92
According to Raults law, PH2O = XH2O * P0H2O = 0.92 * 23.8 torr = 21.896 torr
Part B
Total moles = moles of cyclo hexane + moles of acetone = 1.50 + 2.50 = 4.00
Total vapour pressure = 1.50/4.00 * 97.6 torr + 2.50/4.00 * 229.5 torr = 36.6 + 143.4375 = 180.0375 torr
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