S E U T K A 4 LSAAL'l' AC'1'IOS ~~
os A4cTL)s o L ~ - B I I , I ' l ~ I € ~ s ' . .~
~
R T TS'ILLIAAII NOLAXD H E S D E R S ( 1 S .\XI) H V ( ; H ST()TI' l A Y I , ( )I
.
and neutral salts in the light of recent work on the activity of the undissociated molecule, t o trace out if possible any parallelism The observationq of Ostwald were extended t o acids other than the strong acids, hydrochloric and nitric, both of similar salt effect I t was hoped t h a t a n investigation of other acids and their ialts might yield some points of support for one or the other of the hypotheses which have been put forward
Experimental The method emploj-ed in the present investigation consisted essentially in rotating the s?-stem-acid, solute, and neutral salt in sealed bottles in a well regulated thermostat until equilibrium had been eitablished. Tests were made from time to time t o iniure that the equilibrium point had been reached Half normal acid n a i found to be the most coni-enient strength for the purpose required These acid solutioni were originally of normal concentration in order t o allow for the addition of the neutral salt solution and water sufficient to reduce the normality to one-half. Carefully prepared b a r j t a of knon n itrcngth Y,as used in standardizing the acids The neutral salt iolutioii5 were made twice normal, from material5 of the highest grade procurable, by weighing carefull!- the potassium salt\ and making up to the abo\e normalit? a i t h water In the caic.s of potassium mono- and trichloroacetates the salt solutions ere made u p as follows : A four tirnei normal kolutiori of the acid was carefully prepared and neutraliztd in '1 u hite Forcelain dish with concentrated carbonate-free potassium hj-droxide solution Two hundred and using phenolphthalein as indicator fiftj- cubic centimeters of the four times normal acid were, after neutralization, rnadc up t o fi\-e hundred cubic centimeters, therebj- giving the desired t u ice normal solution of the potassium salt The salts -calcium oxalate and tartrate-used for the solubility determinations were of high grade and quality. A detailed account of the procedure employed in the
.Yeiitral Salt .-iction
OH
A c i d Solubilities
669
present investigation ma!- here be given. Choosing the s>-stem-calcium oxalate, hydrochloric acid, and potassium chloride: 100cc of the normal hydrochloric acid were drawn out by means of a pipette calibrated t o deliver this amount and placed in a calibrated 2 0 0 cc flask which was used for S o n - if 0 .I -1- neutral salt was mixing each solution desired, I O cc of the twice normal potassium chloride solution were added t o the acid in the flask. The mixture was then made u p to 2 0 0 cc with distilled water and, after mixing thoroughly, was poured into a 250 cc reagent bottle which was fitted with a ground glass stopper. These reagent botties were found t o be very suitable as rotating flasks. X small and approximately constant quantity of calcium oxalate was then added, the bottle sealed with paraffine and rotated a t 25' C , the temperature being kept constant to within 0 0 1 degree. The rotation was effected by attachment to spider wheel arrangements suitably fastened on a shaft placed in the thermostat a t an angle of fort\--fi\-e degrees, which shaft was itself driT-en by means of a worm wheel arrangement from the stirring gear of the thermostat This rotation around an inclined shaft enbures a steady and eficient mixing of the se\-eral phases present in the flask. -After the equilibrium point had been reached the bottles were removed from the rotator and suspended in the thermostat ox-er night t o allow the precipitate to settle, since the latter was light and did not settle readily T o prex-ent sdspended particles from being drawn off n i t h the liquid to be analyzed a piece of filter paper was placed over the end of a calibrated pipette and I j o cc of the clear solution were rerno\-ed for analysis. Sufficient ammonium oxalate was added t o insure complete precipitation of the calcium, and the latter \vas precipitated as the oxalate by neutralizing the hot acid solution with ammonium hydroxide. -After standing over night the precipitated calcium oxalate was filtered washed with dilute ammonia solution, ignited in a platinum crucible and weighed as the oxide. T h e appended tables represent the most reliable d a t a
obtained with the se\.eral acids and their corresponding salts. A11 determinations which in any wa:\-seemed doubtful were carefully rechecked and, of the series communicated, several separate and distinct determinations were performed a t each concentration of salt. The results obtained could readily he duplicated. In the case of the weaker acids, in which the osalate of calcium had too small a solubility to crisure accurac!. of working and reproducilility of results, the more soluble tartrate was substituted. 'I'he general lieha\-ior towards solution in the acids and mistures with salts r to var!- consideralily though '!'al)lcs IL. :itid 1. indicate t h a t the magnitude of the influi~riceof the neutral halt varied. 'l'he tahlei which ~ o l l o ~represent v :I summary o f tlic. rcsults ohtainrtl. C'clumii I ;;ivc>G the normalit!- oi the qalt i t i the half norma1 acid mlutioii i~mplo\-etl. 'l'lie second coluniii gi1-c.. t h c weight i i i gr;tiii\ of C a ( oi the c~:ilciuni osalatc or tartrate t l i w ) l ~ ~ ci dn 1 ~ 5 ~c'c': of t h e wlution 111 the last colu m n tlic pcrccnt:txc c1iaiix:c i l l w l L i l ) i l i t > - i, gi\.cii. the 1)ohitii.c \ i y i indicatiiix iiic\rc:i5c., thc. iii'gatii i' sign ;i tleu-easc. ( )rigi 11a 11>. t h ? in \.it i ga t i ( I t i . LY cxr e CY) i i (1 IIc' t et 1 t ) (1c t c rni i t i ? t Ii e \.arintii)ii i i i so1uI)ilit~~ jjro(lilcc.(l I)!, s i l t i n iticrv:isiiig c % o i i L y c i i o .I iioriiial. '!'!iv r v ~ i i l t iIvith \\-c.ak ac'itli \ l i ( i \ t i ' ( l 11 iriterc+t :ittac'!icc! t o t l i e , iriBuc.iii~c.of \-?I->- ~ i i i ; t i l roiireiitratioii. ( ) i s a l t . Half 110riii:~la c 4 c l \ v a \ ~ i i e di i i ;ill r : i ~ c ~ ~ ancl t h t . taljlc. rvfc,r t o ~ 0 1 1 i I ) i l i t i c ~a~t 2 , i (Icgrc.c-. Cciitiq-:i(!c. (
'1%\l demonstrated that the influence of potassium chloride on tlie potentials of hydrogen i i i hydrochloric acid bolutioris seeins t o indicate that the concentration of the hydrogeii ion is iiicreased 11. additioii of salt. This would mean that the la-\\-of mass action or i n other words the theory of isohydric solutions. was iiot directl!- applicahle to the case i n question. On the. other hand. the earlier \vork of \\-alpole? a1o:ig the sanie lilies with mixtures of acetic acid and sodium acetate indicates that in this case the Ian of mass action is obeyed within the limits of the error of the experiment. If some explanation were forthcoming as to why the hydrogeiiion concentration iii hydrochloric acid is apparently increased bj- potassium chloride an expianation of the present phenomena might lie made possiblc. One experiment i n tlie present series is explainable from the standpoint of the results of Hariied. Reference to Table I 1 will ‘how that tlie influence of potassium nitrate on solu1iiIitJ- in hydrochloric w i d is of the same order of magnitude as that of potasslum chloride. This is in accord with the result of Hariied that sodium bromide had a similar influence on the electromotive force measurements to t h a t of sodium chloride. As was s h o ~ v nalso by Harned, this result is in full theoretical accord with the law of mass action as usually applied if the equilibrium constants of the several substances concerned in the equilibrium are equal. T h a t this is substantiall!, true a recent paper of -4rrhenius:’ demonstrates.
Summary
II series oi‘ solubility determinations with hydrochloric, . _
trichloracetic, monochloracetic. and acetic acids in presencr. of varying concentrations of their respecti\-e potassium salts has been made for calcium oxalate and calcium tartrate ab substrate From the eiperimental figures it has been shown t h a t the influence of the neutral salt on solubilitj- is a progressive function of the acid strength, causing greatest de crease for weakest acids and greatest increase for the strong est T h e phenomena in question have been duly considered with regard t o the se\-era1 theories of mass action and intermediate product formation, hydration of salts, and activit? of both hydrogen ion and undissociated molecule, yet no strict mathematical formulation has been obtained t o elucidate the phenomena Keutral salts of uncommon ions have been shown to have effects similar to those pos5essing common ions under certain circumstances
