a. A mixture of 60 mol % n-propylcyclohexane and 40 mol % n-propylbenzene is dis

Question

a. A mixture of 60 mol % n-propylcyclohexane and 40 mol % n-propylbenzene
is distilled through a simple distillation apparatus; assume that no
fractionation occurs during the distillation. The boiling temperature is
found to be 157 ?C (760 torr) as the first small amount of distillate is collected.
The standard vapor pressures of n-propylcyclohexane and n-propylbenzene
are known to be 769 torr and 725 torr, respectively, at 157.3 ?C.
Calculate the percentage of each of the two components in the first few
drops of distillate.

b. A mixture of 50 mol % benzene and 50 mol % toluene is distilled under
exactly the same conditions as in Part a. Using Figure 4.3, determine the
distillation temperature and the percentage composition of the first few
drops of distillate.

Explanation / Answer

(a)

For propylcyclohexane

P = P0* X= 769 * 0.6 = 462.4 torr

For cpropylbenzene

P = P0* X= 725 * 0.4 = 290 torr

P (total )= 462.4 + 290 = 752.4 torr

mole fraction of propylcyclohexane = 462.4*100/ 752.4= 61.45 %

mole fraction of propylbenzene = 290*100/752.4= 38.54 %

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According to the diagram, the solution will boil at 93oC where the composition is 50-50%

composition will be 30 % benzene and 70% toluene

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In case a more efficient fractional distillation is required. Because the boiling point difference of the two pure liquid is very close to the boiling point of the mixture. If the temperature slightly increase the whole solution distill together

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