Chemistry 232
Tutorial Session # 1
G. Marangoni
1.
Date: January 18, 2008.
The densities of solutions of methanol and water of varying composition are given below.
Calculate the volume of 100 grams of each solution and plot either the mean molar
volumes or the mean molar excess volumes of these solutions and determine the partial
molar volumes of methanol and water in these solutions at the following compositions.
a)
0.250
b)
0.500
c)
0.750
d)
a solution composed of 50.00 cm3 of methanol and 50.00 cm3 of water.
Methanol (% by mass)
0.00
5.00
10.00
15.00
26.00
34.00
48.00
52.00
58.00
64.00
70.00
76.00
84.00
96.00
100.0
Density /(g/cm3)
0.99823
0.9896
0.9816
0.9740
0.9576
0.9450
0.9196
0.9114
0.8987
0.8856
0.8715
0.8586
0.8365
0.8034
0.7917
2.
The partial molar volumes of acetone and chloroform are 74.17 cm3/mol and 80.24
cm3/mol at X(Chl) = 0.4693. Find the volume of 1.000 kg of this solution.
3.
How many grams of sucrose (C12H22O11) have to be added to 90.0 grams of water in
order to reduce the vapour pressure above the solution to 95% of that of pure water at 298
K.
Please attempt the following questions. Answers will be posted
on the Chemistry 232 Website.
4.
The densities of solutions of 2-propanol and water of varying composition are given
below. Calculate the mean molar volumes of the solution or the mean mixing molar
volume of 100 grams of each solution and plot either the mean molar volumes or the
mean molar excess volumes of these solutions and determine the partial molar volumes
of methanol and water in these solutions at the following compositions.
a)
0.250
b)
0.500
c)
0.750
d)
a solution composed of 50.00 cm3 of 2-PrOH and 50.00 cm3 of water.
5.
The vapour pressure of benzene at 60 C is 400. Torr. The vapour pressure of a solution
of 19.0 g of an involatile solute in 500.0 grams of benzene was 386 Torr. Obtain the
molar mass of the compound.
6.
At 63.5C, the vapour pressures of water and ethanol are 175 torr and 400 torr,
respectively. Calculate the vapour pressure above a 50.0% by mass mixture of ethanol
and water (assume ideal solution behaviour).
Answers
4.
2-PrOH (% by mass)
0.00
5.00
10.00
16.00
20.00
24.00
32.00
40.00
48.00
60.00
68.00
76.00
84.00
92.00
100.00
Density /(g/cm3)
0.99823
0.9884
0.9816
0.9751
0.9696
0.9630
0.9478
0.9302
0.9113
0.8824
0.8632
0.8438
0.8243
0.8046
0.7848

/(g/cm3)
0.99823
0.9884
0.9816
0.9751
0.9696
0.9630
0.9478
0.9302
0.9113
0.8824
0.8632
0.8438
0.8243
0.8046
0.7848
Mass 2PrOH
0
5
10
16
20
24
32
40
48
60
68
76
84
92
100
Mass
H2O
100
95
90
84
80
76
68
60
52
40
32
24
16
8
0
Vsol'n
100.18
101.17
101.87
102.55
103.14
103.84
105.51
107.50
109.73
113.33
115.85
118.51
121.32
124.29
127.42
mole
H2O
5.55
5.27
4.99
4.66
4.44
4.22
3.77
3.33
2.89
2.22
1.78
1.33
0.89
0.44
0.00
mole
2-PrOH
0.00
0.08
0.17
0.27
0.33
0.40
0.53
0.67
0.80
1.00
1.13
1.26
1.40
1.53
1.66
X2-PrOH
0.00
0.02
0.03
0.05
0.07
0.09
0.12
0.17
0.22
0.31
0.39
0.49
0.61
0.78
1.00
Vmix
0.00
-0.07
-0.20
-0.40
-0.52
-0.62
-0.79
-0.89
-0.96
-0.99
-0.98
-0.91
-0.76
-0.48
0.00
Vmean
18.05
18.89
19.74
20.81
21.61
22.49
24.50
26.91
29.78
35.21
39.85
45.64
53.07
62.93
76.57
Plot of Vsol vs. X2-PrOH
90.00
80.00
70.00
Vsol / cm3 mol-1
%
MeOH
0
5
10
16
20
24
32
40
48
60
68
76
84
92
100
60.00
50.00
40.00
30.00
20.00
10.00
0.00
0.00
0.10
0.20
0.30
0.40
0.50
X2-PrOH
0.60
0.70
0.80
0.90
1.00
Plot of Vmix vs. X2-PrOH
0.00
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
Vmix / cm3 mol-1
-0.20
-0.40
-0.60
-0.80
-1.00
-1.20
X2-PrOH
VH2O /cm3 mol-1
17.1
16.9
15.9
17.4
X2-PrOH
0.250
0.500
0.750
0.191 (50:50)
5.
X Bz 
PBz 386 Torr

 0.965
400 Torr
PBz*
n Bz  6.40 mol
6.40 mol
 6.63 moll
0.965
 0.0350 x 6.63 mol  0.232 mol
nT 
n solute
M solute 
19.0 g
 81.9 g
mol
0.232 mol
V2-PrOH / cm3 mol-1
75.4
75.6
76.5
75.5
6.
Assume 100 grams
50.0 g
n H 2O 
18.02. g mol 1
 2.77 mol
50.0 g
n EtO H 
46.08 g mol 1
 1.09 mol
n H 2O
X H 2O 
n H 2O  n EtO H

2.77 mol
2.77 mol  1.09 mol
 0.718
PH O  X H O PH* O
2
2
2
 0.718 x 175Torr
 126Torr
*
PEtO H  X EtO HPEtO
H
 0.282 x 400Torr
 113Torr
PT  126Torr  113Torr
 239Torr