1090
F. H. MACDOUGALL A N D LEOE. TOPOL
Vol. 56
IONIC EQUILIBRIA IN AQUEOUS AND MIXED SOLVENT SOLUTIONS OF SILVElt ACETATE AND SILVER MONOCHLOROACETA\TE BY F. H. MACDOUGALL AND LEOE. TOPOL’ School of Chemislry, University of Minnesota, Minneapolis Received April 18, 196)
The elcctroniotive forco of cells cont,aiiiiiigsilver ric:ctatc and sodiurn acetate in oiii! half-cell aiitl silver iiitratc and Nodiuiii nitrate in the other half-cell has been nirssured a t 25O, using as solvents 10, 20 and 30% ethanol-water and 10, 20 and 30% acetone-water mixtures. A similar study hits been made with silver monochloroacetate in water, and 10, 20 and 30% ethanol-water mixtures. In unsaturated solutions of silver acetate t n d silver chloroacetate equilibrium constants for the following equilibria have been determined: AgA Ft Ag+ A-; AgA2- + Ag+ 2A-. The relation between the value of a11equilibrium constant and the dielectric constant of the medium is given by the simple Born theory more satisfactorily than one might well expect. The activity-product constants obtained in previous studies of the solubility of silver acetate in various solvents have been corrected by mskina- use of the dissociation constants obtained by means of the electromotive force measurements.
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Introduction In our earlier work in this field,2-5measurements were made of the solubility of silver acetate i i i water and in mixed solvents in the presence of added electrolytes, including acetates and silver salts. Evidence was obtained leading to the view that in these solutions complex ions of the form AgA2- and Ag,A+ were formed. Estimates were made of the dissociation constants of these ions. Values of the activity product, K1 = U A g f a A g were also obtained 011 the assumption that in the solutions investigated silver acetate mas virtually completely dissociated. More recently, electromotive force measiiremei1ts were made of appropriate ~ e l l s . ~These . ~ measurements soon led to the conclusion that in 0.05 M silver acetate in aqueous solution the silver acetate is roughly 85% dissociated. This work also enabled us to obtain a more accurate estimate of Kz, the dissociation constant of the complex ion AgAZ-. In the present investigation, electromotive force studies have been extended to solutions of silver acetate in water-ethanol and water-acetone mixtures arid to solutions of silver monochloroacetate in mixtures of water and ethanol. Preparation of Silver Electrodes and of Solutions.this corincction, it must sufficc to refer to thc paper by JIacDougalI and P~terson.6,~Our silvcr c1cct;rodes were fourid i o agree wit.hin less t81ian0.04 millivolt. It, should bo atldcd t.liat solut,ions oC silver inonocliloroacct,al,(~ undergo H. S ~ J Whydrolysis forming olilorido ion. Tho rate of liytlrolysis increases ait,li i,hc tcnipcra(.uloaiitl dcert!rtsc!s with iii(:rvwiiig pw rent. of alcohol. This type of hydrolysis has I)wn frcqucii1,ly invc:si.igatotl.8 I3ccaausc: of t,lm occur111
( I ) This payer ia based on a thesis prcsrntcd by LCOE. Toid to Glic Graduate School of the Univernity of Minnrsota in partial frilfilliiicnt of thc requirements for thc dcarce of doctor of philosopliy. (2) P. H. MacDougall, J . Am. Chem. Soc.. 69, 1390 (1930); IC. €1. hiacDollgs~l and J. Rehner. Jr., ibid., 66, 368 (1934); P. TI. JlacDorigall and C. E. Bartscli, THISJOURNAL, 40, 649 (111345). (3) E. Larsson and B. Adcll. Z. anorg. alluem. Chew., 196, 354 (1831). (4) F. IC. Rlacl)ougall and W. L). Larson, ‘hiis J O U I t N A L . 41, 417 (l!l37). ( 5 ) F. 11. hlsr*l)r~iigall and AI. hllrn, ;bid., 46, 730 (1042); 49, 245 (1945); 1,’. I f . hlavI~oirgall,ibid., 46, 738 ( I ! l W . (6) F. I t . blnrDnugaIl and S. Prternon. ibid., 61. 1346 (1947). (7) J. V. Parker, C . Hirayama and k’. H. AlacUougall, ibid., 63, 912 (1949). (8) H. M. Dawson and E. R . Pycocli, J . C l e m . Soc., 778 (1934); 153 (1936); H. R.1. Dawson, E. R. Pycock and G . 17. Smith, ibid., 317 (1945); W . -4. Drushel and C. S. Simpson, J . Am. Chem. Soc., 39, 2435 (1917); 8. Matsuura, Bull. Chem. Soc. Japan, 8, 113 (1933); L. B. Nannings. Rec. trav. chin., 69, 76 (1950); G . Senter, Proc. Chem. SOC.. OS, 60 (1907); J . Chem. SOC., 91, 460 (1907); C . Senter and H. Wood
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rence of this hydrolysis, our results with chloroacctate solutions are probably less trustworthy than those with acetate solutions. The compositions of the water-alcohol and water-acetono mixtures were calculated from the densities mcasurcd at, 25’ .9,10 The dielectric constants, D wcrc interpolated from the values given by Akerlof.11 The Experimental Method.-All of the cells investigated were of the type AgA(ci) KNOs AgNOa(Ci’1 Ag NaA(c2) saturated NaNOa(c2’) Ag where the symbol A denotes either the acetate or the chloroacetate radical and where c is the molarity. I n any given cell, the concentrations CI and c: on the one hand and thc concentrations c2 and c: on the other hand were made &s nearly equal as possible. The cells used were similar to those employed by MacDougall and Peterson.6 The potentiometer was a Leeds and Northrup Type K-2 and the galvanometer was of the walltype. The t e m p r a t w e of t,he water-bath was maintained at 25.00 f 0.02 . Electromotive mcasuremcmts were mad(: a t hourly inlervals. Rcadings become const.ant after two to four hours and remained so for periods ranging from two hours t,o eight, days.
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1
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Experimental Data.-Table I gives the results obtained in the measurement of the electromotive force .at 25” of the cells which contained silver acetate in 10% ethanol.I2 TABLE I ELECTRUMOTIVE FORCE DATAOF SILVERACETAI~EAT 25” IN 10% I~THANOL Solvent = 9.23% ct.hanol; & = 0.98159; 1) = 73.24 C2
Cell 1 2
3 4
5 6 7 8 !I 10 11
Cl
A ~ A NaA 0.0083KL! 0 . 7 1 7 8
.0 I :%!I .0 I380 .01 1 I(; .0111ti
.I104 .008500
,005500 ,004502 ,008247 .02206
111ortlcr t.o
‘
CZ’
NaNOa AgNOa 0.008346 0 . 7 1 7 8 ,1025 ,01388 , 102fi .4105 . 4 105 ,01388 ,1434 .OlllF ,1434 ,3534 .01 I I6 ,5538 ,02044 ,01104 .0!044 ,1434 ,1434 ,005W4 ,1025 .I026 ,005504 ,8551) ,8559 .004590 ,2065 ,2056 ,008249 ,02206 .04111 ,04109
lie
I knsity 1 .01:
