T H E SOLUBILITY AND ACTIVITY COEFFICIENT OF SILVER ACETATE I N MIXED SOLVENTS‘ F. H. MAcDOUGALL AND CHARLES EDWARD BARTSCH School of Chemistry, University of Minnasota, Minneapolis, Minnesota Received January 86, 1096 INTRODUCTION
The experimental work described in this paper was undertaken in order to furnish an additional test of the applicability of the theory of Debye and Huckel (2) to strong electrolytes dissolved in mixed solvents. With this purpose in mind, we measured the solubility of silver acetate in various mixtures of water and ethyl alcohol in the presence of various amounts of a soluble nitrate. The nitrates used were those of lithium, sodium, potassium, calcium, strontium, and barium. The solubility of silver acetate in water at 25°C. has been determined by a number of investigators. We give herewith the results obtained in moles per liter: Raupenstrauch (lo), 0.0671; Goldschmidt (3), 0.0669; Jaques ( 5 ) , 0.0663; Hill and Simmons (4),0.0667; Knox and Will (6), 0.0667; MacDougall (7), 0.0664; MacDougall and Rehner (8), 0.0663. The value obtained in the present research was 0.06634. MATERIALS USED
The silver acetate, obtained from Mallinckrodt, was 64.62 per cent silver (theoretical, 64.64 per cent) and was used without further purification. It was kept in black lacquered bottles and stored in the dark. The nitrate salts were recrystallized from “conductivity” water and dried at 150OC. The water was “conductivity” water, nrepared by distillation of distilled water in a tin-lined vessel in the presence of sodium hydroxide and potassium permanganate. The ethyl alcohol used was approximately 95 per cent by volume and was tested according to Murray (9). It was found to be free from acetone, aldehyde, other organic impurities, and heavy metals. It was used without further purification. EXPERIMENTAL PROCEDURE
The mixed solvent was prepared by mixing weighed amounts of 95 per cent alcohol and conductivity water, but the exact alcoholic content of This paper gives the essential portions of the dissertation presented by Charles E. Bartsch to the Graduate Faculty of the University of Minnesota in partial fulfillment of the requirements for the degree of Doctor of Philosophy, June, 1935. 649
650
F. H. MACDOUGALL AND CHARLES E D F A R D BARTSCH
the mixture was calculated from its density. Mixtures containing approximately 10, 20, and 30 per cent by weight of alcohol were used as solvents. Weighed amounts of the solvent and of the nitrate salt were brought together in a glass-stoppered flask. When the nitrate had dissolved, equal portions of the solution were transferred to two amber-colored glass-stoppered bottles containing an excess of silver acetate. The bottles were sealed immediately with a heavy layer of paraffin. They were then rotated end over end in a water bath a t 25.00 & 0.05’C. for a t least forty-eight hours. For the purpose of sampling, the bottles were removed from the rotator and clamped upright and almost completely immersed in the bath. After half an hour, the paraffin was removed from the stopper, a siphon (containing a small cotton wad in the “bottle” end) was inserted in the liquid, and about 125 cc. of the liquid was blown by compressed air into a 250-cc. Erlenmeyer flask, immersed as completely as was permissible in the water bath. The Erlenmeyer flask was fitted with a rubber stopper t o minimize evaporation. From this flask two samples of 50 cc. each were withdrawn by means of an accurately calibrated pipet and weighed in glass-stoppered weighing bottles. Results for density and for analysis were accordingly obtained in quadruplicate for each concentration of added nitrate. The solutions containing 10 or 20 per cent alcohol were analyzed gravimetrically for silver; all other solutions were analyzed volumetrically. The volumetric analysis was carried out by the Volhard method for silver as suggested by Professor I. M. Kolthoff. The samples were transferred to 250-cc. Erlenmeyer flasks, acidified with 5 cc. of concentrated nitric acid, and diluted to 100 cc. Then 5 cc. of ferric nitrate indicator solution was added. The solutions were titrated immediately with 0.04 N potassium thiocyanate to a reddish-brown coloration. The solutions were then shaken until the color disappeared. The titration with potassium thiocyanate was continued until a faint rose coloration remained after vigorous shaking. The thiocyanate solution was standardized with a solution containing a known amount of silver acetate. The standardization was checked with a solution containing a known weight of silver nitrate. METHODS O F EXPRESSINQ COMPOSITION O F THE SOLUTIONS
If p is the fraction of alcohol in the mixed solvent, the number of moles of water, No,, and of ethyl alcohol, No,, in 1000 g. of solvent can be found from the equations 1000 (1 - p ) No, = 18.015 lO0Op
No, =
46.045
SOLUBILITY AND ACTIVITY COEFFICIENT
OF SILVER ACETATE
651
The molar concentration, c, of a solute salt is the number of moles of the salt in a liter of the solution. The molal concentration, m, is the number of moles in 1000 g. of mixed solvent. In calculating the mole fraction of a component of the solution we have assumed that $he dissolved silver acetate and added nitrate salt are conipletely ionized. If z is the mole fracin a solution in which the molalities of silver tion of Ag+ or of C2Ha0i acetate and added nitrate are m and m, respectively, then
where v is the number of ions obtainable on complete ionization of one molecule of added nitrate salt. The density of the solvent (alcohol-water mixture) is represented by do,that of the solution saturated with silver acetate and containing various amounts of nitrate salt by d. ACTIVITY COEFFICIENTS
If f, y, and yo bre the mole-fraction, molality, and molarity activity coefficients respectively of any solute then
f
Y =
ye
(3)
+
2m vma + No,+No,
=
do (1
d
+
m~
+ m.Ma),,
1000
(4)
M and M , are the molecular weights of silver acetate and added nitrate salt, respectively. According to Debye and Hiickel (2), the activity coefficient of a univalent ion (or of a uni-univalent salt) at 25'C. is given by the equations log,,f = log1020
- log102 = - 1 +BASS $ ~
(5)
B = -352.61
Dt
A =
2.914 X lo8a
Dt
(7)
where D is the dielectric constant of the solvent and a is a suitable mean ionic diameter. I n equation 5, z is the mole fraction of silver ion in a given saturated solution and z0is the extrapolated value of z for an ionic strength equal to zero; in other words, $0 is the activity of silver ion in any solution saturated with silver acetate.
652
F. H. IdACDOUGALL AND CHARLES EDWARD BARTSCH
The dielectric constant of an alcohol-wate: mixture was calculated by linear interpolation from the values given by Akerlof (1). EXPERIMENTAL DATA
In table 1 we give the solubility a t 25°C. of silver acetate in alcoholwater mixtures containing from 0 to 50 per cent ethyl alcohol. In tables TABLE 1
Solubility at 25°C. of silver acetate in mixtures of ethyl alcohol and water PER CENT ALCOHOL
SATURATED
TRATIOX O F
0.00 5.00 7.62 9.00 15.03 19,96
1 ,0048 0,9955 0.9898 0.9882 0.9784 0.9696
0.0663 0,0577 0.0523 0.0506 0.0413 0.03
1
25,06 29.82 30,05 40.27 50.14
SATURATED
MOLAR CONCENTRATION O F SILVER ACETATE
0,9616 0.9530 0.9526 0,9323 0.9102
0,0294 0,0251 0.0249 0.0180 0.0124
TABLE 2
Solubility at 25°C. of silver acetate in mixtures of.~ethyl alcohol and water containing potassium nitrate 9 . 4 1 PER CENT ALCOHOL
D
20.37
PER CENT ALCOHOL
= 73.14
D
= GG.78
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