T H E CHANGE IN T H E TRANSFORMATION TEMPERATURE O F COPPER SULFATE AT 56°C. WITH T H E SOLVENT MEDIUM HAROLD J. ABRAHAMS
AND
WALTER W. LUCASSE
The John Harrison Laboratory of Chemistry, The University of Pennsylvania, Philadelphia, Pa. Received August 26, 2932
Studies of the resistance of saturated solutions of copper sulfate in water have shown a break in the curve a t about 56°C. (1). Electromotive force and solubility measurements have likewise indicated a change a t about this point. In summarizing his data, Etard (2) gives two equations, one for the solubility a t temperatures below 55°C. and another for that a t higher temperatures. The change taking place a t this temperature has been variously interpreted as a transition (3) from a n a to a /3 pentahydrate and as the point of formation of 3CuS0~.4CuO.l2HzO. I n the preceding paper, determinations of the transition points of salt hydrates have been given from a study of the resistance of solutions of constant concentration in several non-aqueous solvents. I n all cases, except for solutions of cobalt chloride in ethylene glycol, the transition temperature was found to be the same within the experimental error as that given by other methods. I n this system it was found that the break in the curve was about 1.6"C. below the transition point as indicated by other methods, or about four times the average deviation from the mean value found for this salt in other solvents. The transition temperature in general is lowered by the presence of foreign substances and different methods do not always yield the same value, but it was suggested that the effect in this case may have been due to the solvent. I n the present paper are given results for the transformation of copper sulfate in glycerolalcohol mixtures where the temperature is lowered several degrees. The apparatus and method was entirely the same as in the previous paper. The results are given in table 1 where the resistances a t various temperatures are given for solutions of copper sulfate in glycerol-alcohol mixtures of different proportions. The ethyl alcohol was purified and dehydrated as before. The copper sulfate and glycerol were of high quality and were not further purified. The solvent was made up by volume, seven parts of alcohol and three of glycerol, for example, being used for the 70 per cent alcohol solution. The solutions were prepared by shaking an excess of the pentahydrate with a quantity of the mixed solvent 521
522
HAROLD J. ABRAHAMS AND W A L T E R W. LUCASSE
in an air-tight container. After settling, a portion of the supernatant liquid was transferred to the cell. TABLE 1 The resistance of copper sulfate i n glycerol-alcohol mixtures BERIEFJ
1
Temperature
Reaistance
42 44 46 48 50 52 54 56 58 60
4234 3985 3759 3532 3353 3164 3004 2845 2760 2561
LIERIES
Temperature
36 38 40 42 44 46 48 50 52 54 56 58 60
I
6
1
FJERIES
Temperature
30 32 34 36 38 40 42 44 46 48 50 52 54 56 58
I
2
Temperature
5756 5302 4899 4538 4180 3874 3605 3333 3117 2920 2734 2579 2405
40.2 42 44 46 48.2 50.4 52 54 56 58 60
I
3
Temperature
Resistance
13500 12180 11130 10150 9256 8408 7698 7043 6398 5864 5388 4975 4661 4314 4025
42 44.2 46 48 50 52 54 56 58
2976 2811 2689 2552 2427 2313 2209* 2097 1998
SERIEFJ6
Resistance
BERIES
Resistance
Resistance
2546 2397 2230 2092 1946 1814 1732 1623 1536 1444 1365
I
-
SERIES
Temperature
42.2 44 46 48 49 50 52.2 54 55 56 58
1
1
7
Resiatance
15590 14380 13170 11930 11410 10960 9908 9182 8822 8476 7807
SERIES
Temperature
40 42 44 46 48 50 52 54 56 58 60 62
I
4
Resistance
2226 2120 2012 1913 1816 1734 1653 1572 1498 1434 1374 1312
SERIEB
I
8
Tempera- Resiatance ture
40 42 44 46 48.4 50 52 54 56 58 60.2 62 64
9577 9124 8699 8333 7887 7658 7330 7019 6765 6494 6236 6038 5823
In all cases, plots of the data obtained showed breaks in the curves a t temperatures below 56°C. Constants for the equation log R = a
+ bt
for the portion below and above the break were calculated and the values of the transformation temperature calculated as in the previous paper. In
523
TRANSFORMATION T E M P E R A T U R E O F COPPER S U L F A T E
table 2 the results are listed according t o the increasing alcoholic content of the solvent. The series number given in the first column refers to the data in table 1 and gives the order in which the determinations were made.
TABLE 2 The transformation temperature of copper sulfate SERIES
PER CENT ALCOEOL
7 2 5 6
20 30 50 60 70 80 80 90
1
3 4 8
a
10zb
5.0385 4.7283 4.3700 3.9936 4.1621 3.9381 3.7850 4.3649
-2.002 -2.004 -1.698 -1.463 -1.276 -1.106 -1.094 -0.9635
a'
4.9587 4.5172 4.2248 3.9094 4.1066 3.9087 3.7342 4.2855
t
ioza'
-1.841 -1.576 -1.405 -1.292 -1.164 -1.048 -0.9949 -0,8140
49.6 49.3 49.6 49.2 49.6 50.7 51.3 53.1
9)
L
20
bo
YO
80
% Aicoho1
Comporit i o n o f glycerol -alcohol migt u t e FIG,1
The third and fourth columns give the values of the constants for the equation below the transformation temperature and the next two columns the corresponding values for the curve above this point. In the last column
524
HAROLD J. ABRAHAMS AND WALTER W. LUCASSE
are listed the calculated transformation temperatures of the salt in the solvent of composition given in the second column. A plot of these temperatures as a function of the alcoholic content of the solvent is given in figure 1, where the abscissae show the solvent composition and the ordinates the corresponding temperatures. Measurements in solutions of lower alcoholic content were difficult because of the high viscosity of the glycerol, and at higher concentrations because of the slight solubility of copper sulfate in alcohol. The smooth curve passing through the experimental points has been extended as a broken line in each direction to the pure components of the solvent. The previous studies have shown that the transition points of the various salts used have been the same in solutions of ethyl alcohol as the values determined by other methods than the one used here, and the form of the curve with increasing alcoholic content makes it logical to extrapolate to 56°C.as the temperature a t which the transformation would take place in this solvent, could sufficient amount be dissolved to determine the point. It is possible that a t concentrations of glycerol greater than 80 per cent the curve again rises rapidly to 56°C. Should the curve be of that form, i t would show the mutual lowering of the transition point by the added component of the solvent in each case. I n the range measured, however, the curve shows no tendency t o rise in the region of higher glycerol content. In view of the work with other solvents and with alcohol-water mixtures, it seems unlikely, also, that traces of water or other impurities in the glycerol would lead to a constant depression in the material used. Nor does it seem likely that the form of the curve shown in the figure is due to any reaction or dehydrating effect of the glycerol. The measurements for series 1,3,5,and 7 were carried out as soon as the solutions were made up; those for 2, 6,and 8 about five hours after making the solutions; and for series 4 about forty-eight hours after. It appears from this study, therefore, that copper sulfate undergoes a definite transformation a t about 56°C.and that this temperature may be lowered by the solvent medium (4). As in all of the cases studied, since the solutions were saturated only at room temperatures, the break in the curve is due to a change in the system as a whole and not to the different temperature-solubility relationships of the two forms. Conclusions as to whether this change is between two forms of the pentahydrate or of a more complicated nature cannot be drawn, although it would seem that the formation of the compound indicated above would cause a more pronounced break in the temperature-resistance curve. REFERENCES (1) COHEN:Z. physik. Chem. 31, 164 (1899). (2) ETARD:Compt. rend. 104, 1615 (1887); Ann. chim. phys. [7] 2, 503 (1894). See
however, AGDEAND BARKHOLT: Z. angew. Chem. 39,851 (1926). (3) Landolt-Bornstein Tabellen, Volume I, p. 651. J. Springer, Berlin (1923). (4) MACLEOD-BROWN: Chem. News 109, 123 (1914).
