Hydrogen potentials of mixtures of acetic acid and sodium acetate / by G.S. Walpole.

  • Walpole, George Stanley.
Date:
[1914?]
Catalogue details

Licence: In copyright

Credit: Hydrogen potentials of mixtures of acetic acid and sodium acetate / by G.S. Walpole. Source: Wellcome Collection.

    19/26 page 2517
    question. Points A and B, representing the change of E.M.F., jorrected for diffusion potential, on twenty-fold dilution, of 0'2(W- icetic acid and “standard acetate” respectively, have been deter- i uined with the highest possible accuracy, using special electrodes i md a silica electrode vessel. These form part of a series of deter- ninations to be published in a later paper. It will be seen that the rough statement that the hydrogen Dotential of acetic acid—acetate mixtures is independent of dilution lolds rigidly for only one particular acetic acid-acetate mixture, and is, with the exception of solutions approximating in composi- *■ tion to pure sodium acetate, more nearly correct for solutions that are more alkaline than those which are more acid than “standard Acetate,” The Electrometric Standardisation of Sodium Acetate. If 20 c.c. of iV-hydrochloric acid and 20 c.c. of TF-sodium acetate [ are mixed, an error of 1 in 1000 in the relative strengths of the hydrochloric acid and sodium acetate solutions, or in the measure¬ ment of either, would produce an error of O'94 millivolt in the potential reading of a hydrogen electrode in equilibrium with the : solution. Now this mixture, if the measurement of the liquids is theoretically exact, is a solution which is 0'20iV with respect to both sodium chloride and acetic acid. In spite of its sensitiveness to strong acids, and the salts of strong bases and weak acids, it can I be reproduced readily with great exactness from pure JT-sodium chloride and N-acetic acid, and, moreover, since [H*]= JklHAc]= Jka(C- [IT]), B slight error in the concentration of the acetic acid will have a still smaller effect on the hydrion concentration of the solution. These facts have been made the basis of the method employed bo prepare iF-sodium acetate solution. I have adopted the defini¬ tion: “ Normal sodium acetate solution is a solution of pure sodium acetate of such concentration that when 20 c.c, are taken, mixed with 20 c.c. of iT-hydrochloric acid, and diluted to 100 c.c., the potential of a hydrogen electrode in equilibrium with it is the same as that of a hydrogen electrode in equilibrium with a solution 0'20 normal with respect to both acetic acid and sodium chloride.” To facilitate the preparation of normal sodium acetate in accord¬ ance with this definition a small part of the lower curve of IFig. 1 is reproduced in Fig. 3 on a different scale. The E.M.F. lvalues have been taken, however, from column 6, and not column 8, and are therefore the direct results obtained against the decinormal electrode when the connecting fluid is saturated potassium chloride solution. The rapid change of E.M.F. with the composition of the
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