Question

Some vapor pressure data for ethanol/water are given below.

From this data, determine the Henry’s Law constant for each substance.

XEthanol	PEthanol (/torr)	PWater (/torr)
0.00	0.00	23.78
0.02	4.28	23.31
0.05	9.96	22.67
0.08	14.84	22.07
0.10	17.65	21.70
0.20	27.02	20.25
0.30	31.23	19.34
0.40	33.93	18.50
0.50	36.86	17.29
0.60	40.23	15.53
0.70	43.94	13.16
0.80	48.24	9.89
0.90	53.45	5.38
0.93	55.14	3.83
0.96	56.87	2.23
0.98	58.02	1.13
1.00	59.20	0.00

Estimate, based on your plot, the composition of the distillate resulting from the room temperature distillation of a solution of X_Ethanol = 0.25.

Answer 1

Henry's law states that at a constant temperature, the partial pressure of a gas that dissolves in a given volume of solution is proportional (approximately) to its mole fraction in the solution.

p(ethanol)=KH*X(ethanol) ,KH=Henry's law constant

KH(ethanol)=p(ethanol)/X(ethanol)

KH(water)=p(water)/x(waterr)

A plot of X Vs p gives a straight line graph (linear) of the form y=mx+c with slope =m=KH,intercept=c=0

p (y-axis) and X(x-axis)

KH for ethanol from graph=50.387 torr

Xethanol=0.25

p(ethanol)=50.387 torr*0.25=12.597 torr

KH for water from graph=18.066 torr