As the concentration of a solution increases, its vapor pressure decreases. For
ID: 592716 • Letter: A
Question
As the concentration of a solution increases, its vapor pressure decreases. For s nonvolatile solute B in a iquid solvent A, the relationship between concentretion and vapor pressure is expressed by Raoults aw if 0.490 mol of a nonvolatle nonelectrolyte are dissolved in 3.00 mol ofwater, what is the vapor pressure P,o of the resuiting solution? The vapor pressure of pure water is 23.8 torr st 25 C Express your ans wer with the a Hints where PA is the vapor pressure of the solution, XA is the mole fraction of solvent, snd is the vspor pressure of the pure solvent In a two-component solution consisting of A and B, tho mole fraction, X of component A is defined as PLo 20.5 toir Submit My Answers Give Up Incorrect; Try Again; 4 attempts remaining Solutions containing volatile solutes In solutions composed of two lquids (A and B each iquid contributes to the total vapor pressure above the solution. The total vapor pressure is the sum of the partial pressures of wherP, and are the vapor pressures of pure A and B. respectively. Part B A solution is composed of 1.50 mol cyclohexane Express your answer with the appropriate units 97.6 torr) and 2.50 mol aceo 229.5 torn. What is the total vapor pressure iotal above this solution? Hints Pold-180 torr Submit My AnswerS Give Up Correct similar manner but would involve three terms rather than two. For third volatile oomponent had been present in this solution, the total pressure would be calculated n example total 'a Part C As you saw in Part B, the vapor above the cyalohexane-acetone solution is composed of both cyolohexane vapor and acetone vapor What molo fraction of the vapor above the solution, X (vapor). is cyclohexane? Express your answer numerically. Hints Xey(vapor) Submit My Answers Give UpExplanation / Answer
Part A)
mole fraction of water = moles of water/total moles
= 3.90/(3.90 + 0.480)
= 0.89
So,
vapor pressure of solution = moles fraction of water x vapor pressure of pure water
= 0.89 x 23.8 torr
= 21.2 torr
Part B)
Total moles = 1.5 + 2.5 = 4 mol
total vapor pressure of solution,
= (1.5/4)97.6 + (2.5/4)229.5)
= 180.04 torr
Part C)
mole fraction of vapor which is cyclohexane = moles of cyclohexane/total moles
= 1.50 mol/4 mol
= 0.375
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