THE DETERMIXXTIOX O F VhPOUR h N D LIQUID COMPOSITIONS I N BINARY SYSTEMS 11. ACETOSE-M'ATER A T 25°C'. BY W. G . BEARE, G . A . McVICAR .45D J . B. F E R G U S O S *
In 1900, Taylor' made a preliminary investigation of this system at z5OC. and more recently Morton2 completed a study of it at zo°C. Our own work dealt not only with the vapour and liquid compositions but also with the formula weight of acetone vapour at various pressures and the vapour pressures of dried and of slightly moist acetone at several temperatures.
Apparatus The original apparatus of Ferguson and FunnelP was modified so that the reaction chamber was immersed directly in the large water bath which had one side of plate glass. The temperature of the reaction chamber was thus rendered less dependant upon the fluctuations in the line voltage and less attention was required for a proper temperature control. From the air chaniber, copper sheeting was extended to below the water surface and the glass leads thus enclosed. This sheeting was in turn surrounded by a second copper sheath which was separated from the first by a large air space. The glass leads were thus amply protected from the cold air of the room. The use of the large water bath permitted the stopcock on the vacuum and mercury lines to be re-arranged so that the leads in the former were very desirably shortened. The magnetic hammer, A, and its connecting tubes were moved to the right of the air bath and the lead for t.he vacuum pump mas brought well down into the lower air bath before it emerged. Stopcock, 3, was removed and the mercury in both U tubes was controlled by a single stopcock. (See Ferguson and Funnell, Fig. I ) . The total volume of the vapour was 3477 cc. and the volume of vapour trapped off was 3 3 7 2 cc. These volumes are not those of the apparatus but those the vapour would occupy if at the temperature of the large air bath and differed from the actual volumes by a small correction. The water bath temperature was read on a Beckmann thermometer which was compared with a standard mercury thermometer which in turn was checked a t the transition temperature of Glauber's salt, 3 2,384OC. The temperature of the water bath was kept constant to + o.01"C. The large air bath was usually three degrees hotter than the water bath and kept constant to =to.r°C. during the critical periods of each experiment. The upper air bath was maintained a t 50 j, o.s"C. The manometer was read to 0.1mm. * This investigation was carried out by Messrs. Beare and McVicar under the direction of Prof. Ferguson. 'Taylor: J. Phys. Chem., 4, 3 j j (1900). * Morton: J. Phys. Chem., 33, 393 (1929). Ferguson and Funnell: J. Phys. Chem., 33, I (1929).
VAPOUR AND LIQUID COMPOSITIONS IN BINARY SYSTEMS
1311
Procedure A sample of known weight and composition was distilled into the evacuated apparatus using liquid air as a refrigerant. The mercury columns mere adjusted, the liquid air removed and the sample condensed in the reaction chamber. The air and water baths were brought up to their respective temperatures and the gas circulating pump started. After the pressure had been constant for at least an hour, the pump was stopped, the temperatures and pressure read and the sample trapped off by means of the mercury in the U tubes. The sample was then condensed in the small bulb using liquid air, and the bulb sealed off. I t was weighed, emptied, dried and re-weighed, allowance being made for the buoyancy of the air. This procedure was found to give slightly more consistent results than that used by Ferguson and Funnell.
Calculations The formula weight of acetone vapour was calculated using either the weight of the condensed vapour or the initial weight of the whole sample. In a few experiments, both methods were employed in order to check the experimental procedure. The vapour compositions and liquid compositions were obtained by the following two methods: (I) The weight of the total vapour was found from the weight of the yapour condensed, and the weight of the residue was obtained by difference. The composition of the residue was obtained from a total pressure curve and the composition of the vapour then calculated.
The composition of the condensed vapour was calculated from its (2). weight, original volume, temperature, and pressure; first on the assumption that the vapour was a perfect gaseous solution, each component having a normal formula weight, Le. 18.02 for water and 58.0j for acetone; a correction was then applied based upon the calculated partial pressure of acetone and the formula weight of pure acetone at this pressure. The total weights of the liquid and vapour were obtained as in ( I ) and the composition of the liquid calculated.
Materials (I).
Stock acetone, C. A. F. Kahlbaum's best pre-war acetone: Xus der
Bisulfit Verbindung.
A specific gravity determination gave D T = 0 . 7 9 2 3 6 .
This indicated a water content of 0.4 p e r ~ e n t . ~ Dried acetone; I j o cc. of the stock acetone was left over 50 grams of (2). pure calcium chloride for three weeks in the cold and shaken a t frequent intervals, then decanted off and distilled. The final product had a specific gravity of D T = 0.79072. The following values for dried acetone are given
' Young: "Distillation Principle8 and Processes," 261 (1922).
1312
W. G. BEARE,
G. .4.
JlcT'ICAR A S D J. B. FERGUSON
in the literature: 0 . j 9 0 0 7 , ~0 . 7 9 0 8 2 , ~0.j912,' 0 . 7 9 1 2 , ~o . j 9 0 1 ~and 0 . i 9 0 3 . ' ~ We therefore concluded that our dried acetone was practically free of water. Formula Weight Determinations The effect of pressure on the formula weight of pure acetone was previously investigated by Sameshirna." His results are included with our own in Table I. The variations in Sarneshima's results may have been due to the
TABLEI The Formula Weight of Pure Acetone Beare and IIcVicar 28OC. Sameshima 25OC. Pressure
83 mill 125.6 '32.7 147.2 '59.8 191.6
*
Pressure Formula Weight uncorr. corr. *
Formula Weight Method (1)
(2 )
57.82 58.41
58.01 58.41 58.42 58.;8 58.64 58.79
j6.7 nim i8.6 63.7 110.7
114.2 I
16.7
124.2 163.4 166.1 1j4.3 Corrected by Sameshima using van der Waals' equation.
5 j.99
ji.92
q8.47 58.48 58.64 58.37 j8.j8
58.39 58.39 58.49
I
58.4j 58.66 j9.08 59.06
58.22
58.42 58.29 58.44 58.86
58.82
TABLE I1 The Formula Weight of Pure Acetone Vapour calculated from Experimental Results obtained with Stock Acetone Temperat w e 29.5'c. 36.2 36.1 28.2 28.2 28.3 36.1 29.0 27.8 36.1 28.0 28.2
Pressure 125.1 mm 130.3 135.1 137.7 '37.9 164.0 197.1 199.1 203. j 221.9 224.4 224.9
Formula Weight (Method (2) 58.11 58.25
Method
(I)
58.20 58.03
58.64 58.84
International Critical Tables, 3, 27 (1928). Price: J. Chem. SOC.,115, 112 (1919). Reilly and Ralph: Proc. Roy. bublin Soc., 15, 598 (1919). SBramley: J. Chem. Soc., 109, 455 (1916). Perkin: J. Chem. SOC.,45, 478 (1884). l o Squibbs: J. Am. Chem. SOC., 17, 187 (1895). 1' Sameshima: J. Am. Chem. Soc., 40, 1482 (1918).
E
7
58.22 57.88 58.62 58.48 58.96 59.00 58.87
58.79 58.76
V.4POUR A S D LIQUID COMPOSITIONS I N BINARY SYSTEMS
Weight Percent Acetone in Liquid
FIG.I System Acetone-Water. Total Pressures at 25°C
FIQ.2 The Liquid and VaDour Comnosltions for the System Acetone-FTater at 2 5 T .
13 13
I314
TV. G. BEARE, G. A. McVICAR AND J. B. FERGUSON
fact that he used very small samples. Variations of similar magnitude were noted by us in our preliminary study in which we used stock acetone and calculated the formula weight of pure acetone vapour on the assumption that the vapour in each experiment was a perfect gaseous solution. We thought that these were due in part to our inexperience and in part to the uncertainty in the water content since a differenceof 0.I wt. percent would cause a difference of 0 . 2 in the calculated formula weight. These preliminary measurements are given in Table 11. Owing to the nature of the relation existing between the vapour and liquid compositions in this system, we found it impossible to get accurate measurements of the formula weight of acetone in mixed vapours containing much water vapour. Vapour Pressure Determinations The vapour pressure of pure water was determined a t 2 j"C. and found to be 23.7 mm, the value in I.C.T. being 23,7 j6 nim. Our vapour pressure measurements on dry and moist acetone are given in Table I11 which also includes the measurements of previous workers*? at the temperatures listed. Sameshima's results are essentially those given in I C.T. The vapour pressures of
TABLE I11 The T-apour Pressure of Acetone a t T-arious Temperatures Tempera- Price ture 2 o o c . 186.3 2 j 232.0 30 284.6
35
348.1
Regnault 179.6 281.0
Sameshima 184.8 229.2 282.7
Taylor
346.4
343.0
182.5 229.0 281.0
Beare and McVicar Dried Ac. Stock Ac. 184.5 183.6 229.6 228.0 283.7 282.3 347.7
345.7
the solutions are given in the subsequent tables. In figure I, our results and those of Taylor are plotted against liquid composition on a weight percent basis. As the liquid compositions were obtained by method (2), the total pressures curve affords a good check on the concordance of our experimental results. Taylor's results are indicated by the crosses. Pressures are recorded in this paper in millimeters of mercury a t 0°C. Vapour and Liquid Compositions For these experiments, stock acetone (99.67,) was used and allowance was made for the water present. Our results are given in Table IV. The mol. percentages given here are empirical, based upon the formula weights 18.02 for water and 58.05 for acetone. Experiments Nos. 3, 7 and g were carried out after the total pressure curve was established and were calculated by method (I). For the other determinations method ( 2 ) was employed. The results are given graphically in Fig. 2 . The upper curve gives the weight Price: loc. cit.; Sameshima: loc. cit.; Taylor: 100. cit.; Regnault: MBm. de Paris, 26, 339 (1862).
VAPOUR ANB LIQUID COMPOSITIONS IN BINARY SYSTEMS
0
e
N
P
W,
.
.
0
O
N
N
O
m
a
o
w
?
?
O
h
*
?
I.
x
W
o m r ?
m
?
?
o v i m
W m
E d
m m
m
r?
H
10
d
h
P-
m m
m
m W
X
X
m
CI:
m
d
0 N
X X
N c
d
m
X
9
r?
X
m
* d
?
N
H
3.
o
5 2
10
O
N
Y
n
? ? ? H
Y
m
? 3
n
W
N
d
3\
r?
IC m
n ?
m
10
c\
3.
m
rn
?
m
m w
m 3
*N
?
?
H
w
I
W N
I
m m N
c\
P h
E 0
N m
10 d
m
m
1N 0
VI
m
m
c
2 0 r-
h
N
W r-
N
*
m m
m
3
v,
3\
W r?
r3
m
W
2
r?
1315
a
? '3
h
G.
?
v)
m
t 0
W m
Y
m
H
N
d
G.
2 a2 G.
m N W
r-
h
e
N 3\
e
.e
, m
r. - e
m N
o
E
d
N
3
W
m
0
CC h
N O
W 1 N 0
-
r-
3
n
r?
G. H
O
W m
W
0
0
0
m m
W
? P 0
m
h
h
7
m m
W N
d
m
h
10 0
0 N
N N
m m ? m
d
H
H
o\
m E
m m n
9
?
Y
c
W G.
H
W
":
W N
*,-
m e
I
?
h
H
P-
W
10
h N
m v)
N h
rd
'D,
0
c
H
e
m
*
oc r? m c
W
3
h H
i
* I
3
r N
W H
N m 2 ? G. m W
h
0
G.
N
m m
rr:
m m
"1 m
? 2 m
0
I
m
o \ G. H
2
m m
*
W G.
c
N
?
e
m N G.
10
Cd C
N
H
?
m
"0. W 0
w d
? 09 N
N
1316
W. G. BEARE, 0.A . YcT’ICAR A X D J. B. F E R G U S O N
percent acetone while the lower curve gives the empirical mol. percent. Taylor’s results are given by crosses on the upper graph. A consideration of our results indicates that several points are a little off the smooth curvc Of these points Xos. 7 and 9 were obtained by method ( I ) and the deviations may be due to errors in the determination of the liquid composition by means of the total pressure curve. KO. I I appears to be slightly low in acetone and there must have been some accidental error in this experiment. These deviations are hardly noticeable on the weight percent graph but show up more prominently on the mol. percent graph which magnifies these errors.
Discussion Sameshima thought that the increase in the formula weight of acetone vapour with pressure, was caused, in part, by adsorption on the walls of his apparatus which had a volume of 267.91 cc. and was probably constructed of soft glass. He does not’ give the dimensions of the vapourizing chamber but it is most improbable that the ratio of exposed surface to volume would be similar t o the ratios for our apparatus. The latter were 3477/1848 and 3372/1106, respectively, for the total system and for the part cut off by the Ltubes. Our apparatus was constructed of Pyrex glass. Although adsorption errors may effect the determinations to the extent of 0.1 to 0.2 in the calculated formula weight, the increase is apparently a real one. The vapour and liquid compositions are in fair agreement with the earlier results of Taylor. The simple distillation method, used by him, could not be expected to yield exact results especially with solutions weak in acetone. Evidently the distillation m e t b d , when carefully used, may yield results which approximately indicate the relations in such a liquid system. I n the ideal case, the product, of the total pressure and the mol. fraction of a component in the vapour gives a partial pressure, a simple function of which is a measure of the thermodynamic potential of that component. This partial pressure may then be used to check the experimental results by means of the equation of Duhem-RIargules. In practice, the question arises as to whether the calculated partial pressures may legitimately be used in this manner. As a first approximation, we have assumed that the deviations from the behaviour of perfect gaseous solutions shown by the acetone-water vapours are due to the variation in the forniula weight of the acztone vapour with pressure. The potential of the acetone in the vapour would then bp identical with the potenbial of pure acetone vapour at the same temperature and a t a pressure equal to the partial pressure calculated using the forniula weight for acetone vapour corresponding to this pressure. Now it so happens that the partial pressures calculated in this manner differ but slightly from those calculated using a formula weight of j 8 . 0 j for the acetone vapour. This is indicated by the values given in Table V. The former are listed as actual while the latter as empirical partial pressures. One should not conclude that, because these pressures are practically identical, the effect of pressure on the formula weight may be neglected. This would involve the assumption that acetone vapour was a perfect gas, an
1317
VAPOUR A S D LIQUID COYPOSITIOSS I N BIPiARY SYSTEMS
Emp. Mol. Percent Acetone in Liquid
FIG.3 Total and Partial Pressures for the System Acetone-Water a t zj"C.
TABLE
v
The Total and Partial Pressures for the System Xcetone-Rater at Reference No.
Total Pressure
I
23.7
2
50.1
5 4
61.8 81.3 91.9 126.1 126.6 144.3 I j0.6 '59.8 176.1 184.4 199.1 213.j 229.6
6 7 8 9 IO
I1 I?
I3
'4 15
Empirical pressures water acetone
Actual pressures water acetone
23.; 23.9 23.4 23.0 22.1
26.2 38.4 58.3 69.8
23.7 23.87 23.4 23.0
20.8
10j.3
20.7
105.4
20.1
106.5
20.0
106.6
19.9 18.6 19.8
124.4
20.0
'23.3
19.3 16.7
132.0 140.6 155.9 16j.1 182.4
131.8 '40.3 1jj.8 164.8
12.4
201.1
18.8 '9.5 20.3 19.6 16.9, 12.4
0
229.6
20.2
0
22.1
0
0
26.23 38.41 j8.28 69.76
182.2 201.1
229.6
2
j"C.
1318
W. G. BEARE, G. A . McVICAR AND J. B. FERGUSON
assumption that a change in formula weight from 58.05 to 58.8 involves a negligible energy change. Since we do not know anything about this energy change, we have plotted our partial pressures against empirical mol. percent acetone in the liquid and these and the total pressures are given in Fig. 3. Since the experimental errors are magnified by such plotting, the curves are as smooth and as regular as one would expect were there no formula weight complication. They appear to agree with the Duhem-Rlargules equation, although from the nature of the case the comparison is not an exact one.
Summary The apparatus designed by Ferguson and Funnel1 has been used to study the system acetone-water. The study included: ( I ) . The formula weight of acetone vapour a t various pressures. (2). The vapour pressures of dried and moist acetone a t zoo, z s o , 30' and 3 j"C. (3). The liquid and vapour compositions for the system a t 25'C. (4). The total pressures at z j"C. The results are briefly discussed. Department o j Chemistry, University of Toronto, October 16, 1999.
