The acidic dissociation of many acids has been studied in detail, but weak bases have genera lly been neglected because of t he experimental difficulties encountered in the investigation of some of their buffer solutions by electromotiye-force methods. These difficulties may arise from volatility of the free base or the existence of extraneous electrode reactions such as the formation of ammine complexes at the s ilver-silver-chloride electrode. In th is study of ammonia, special saturators were used to prevent, insofar as possible, t he removal of ammonia from the solutions by the hydrogen gas. A co rrection was applied for the amou nt of diammine silver complex formed at the sil ver-silver-ch loride electrode, a nd t his silver ion was prevented by mechanical means from reaching the platinum electrodes.With these precautions, the acidic dissociation constant of ammonium ion at 0° to 50° C was determined f rom electromotive-force measurements on 19 b uffer solutions containing equal molalities of ammonia and ammonium chloride. The changes of free e nergy, heat content, entropy, and heat capacity that accompany the dissociation processes in the standard state were derived from the temperatu re coefficients of the acidic dissociation constant of ammonium ion and of the basic dissociation constant of ammonia. The activity coefficient o[ ammonium chloride in equ imolal buffer solutions at 25° C was calcu lated.
:TWf! nty-three butTer solu tions composed of approximately eCJual molal amounts of monoethanolamine (2-aminoethanol) and monoethanolammoniurn chloride ill water were studied by electromotive-force methods at 11 temperatures from 0° to 50° C. The values obtained for the acid ic dissociation constant, K bh , of the ethanolammonium ion are given in this range of temperatures bywhere T is the temperature on t he K elvin scale. The changes of free energy, heat content, entropy, and heat capacity that accompany the dissociation of 1 mole of ethanolamm.onium ion in the standard state were calculated from the dissociation constant and its tem perature coefficient. Dissociation of a mol e of ethanolammonium ion resu lts in a small decrease of h eat capacity. In this r espect ethanolammonium ion resembles ammonium ion rathe r than the methyl-substitu ted ammonium ions, for which rather large increases of heat capacity on di ssociation have been found.
The effects of small amounts of dissolved impurities on the potentials of silver-silverhalide electrodes immersed in solutions of alkali halides were studied. Traces of bromide exert disturbing effects on the potential of the silver-silver-chloride electrode. A convenient method for determining small amounts of bromide in the presence of chlorides and a satisfactory means of purifying sodium and potassium chlorides for precise electrochemical work are outlined. The procedure involves treatment of a saturated solution of the salt with chlorine, two successive precipitations with hydrogen chloride, and fusion of the airdried product. A method for diminishing hydrolysis of the salts during fusion is described.
I. Effect of Dissolved Impurities on the Potentials Silver-Halide Electrodes Immersed in Solutions Halidesof Silverof Alkali Small amounts of bromide are known to exert a large effect on the potentials of the saturated calomel electrod3 [1] 1 and the silver-silver-chloride electrode [2, 3]. Sodium chloride and potassium chloride, sufficiently pure for many physicochemical purposes, may, because of the presence of small amounts of bromide, be quite unsuitable for the most precise electromCltric work. A series of emf measurements was made to obtain quantitative information regarding this effect and to ascertain whether some of the other common impurities have a similar disturbing influence.
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