Below is a benzene - toluene pressure - composition diagram for a constant tempe
ID: 898656 • Letter: B
Question
Below is a benzene - toluene pressure - composition diagram for a constant temperature of 298 K. Use this diagram to answer the following questions. Is the solution an ideal solution? Suppose that the pressure and the composition corresponds to point d, and you increase the pressure. At what pressure would you first observe condensation of liquid? Suppose that you increase the pressure to point c. At point c liquid and vapor are in equilibrium. What is the composition of the vapor corresponding to point c? What is the composition of liquid corresponding to point c? What would be the approximate ratio of the total number of moles in the vapor to the total number of moles in the liquid at point c. Suppose that you increase the pressure to point b. At point d liquid and vapor are still in equilibrium. What would be the approximate ratio of the total number of moles in the vapor to the total number of moles in the liquid at point b. Suppose that you continue to increase the pressure. At what pressure would all of the vapor have condensed into liquid? What would be the composition of the last vapor that condensed?Explanation / Answer
A. The solution is not an ideal solution. The actual liquid-vapour curve deviates from the ideal curve.
B. From the curve it is seen that at a pressure around 56 torr the condensation of liquid is observed first.
C. The horizontal line drawn from the point C intersects the vapour curve at 72 % of Benzene composition. So, the vapour contains 72 % of Benzene and 28% of Toluene.
D. The horizontal line drawn from the point C intersects the liquid curve at 45 % of Benzene composition. So, the vapour contains 45 % of Benzene and 55% of Toluene. This observation is justified. Boiling point of toluene (110.6 oC) is higher than that of benzene (80.1 oC). So, at liquid phase content of toluene will be higher than that of benzene.
E. No. of moles in vapor phase : No. of moles in liquid phase
= Distance of liquid line from point C : Distance of vapor line from point C
= 8 : 1 (Aprox.)
F. No. of moles in vapor phase : No. of moles in liquid phase
= Distance of liquid line from point B : Distance of vapor line from point B
= 1 : 4 (Aprox.)
G. From the curve it is seen that at a pressure around 76 torr the condensation of liquid is over.
H. At the point of last condensation the composition is 70% of benzene and 30% of toluene. This composition is identical in vapor as well as liquid.
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