Determination of hydrogen ion concentration

To determine the acidity constant of chloracetic acid in water by kinetic determination of the hydrogen-ion concentration. 

Bronsted and Grove (J. Amer. Chem. Soc. 1930, 52, 1394) showed that the hydrolysis of dimethyl acetal in water is specifically catalysed by hydrogen ions there is no spontaneous reaction, nor does the reaction show general acid catalysis. Their measured values of the first-order rate constant k, determined by a dilatometric method in solutions of perchloric acid over a range of concentrations in water at 20 °C are given in table 1. 

Grove (J. Amer. Chem. Soc. 1930,52,1404) studied the rate of hydrolysis of the acetal in solutions of chloracetic acid at 20 X and obtained the results given in table 2, each recorded value being the mean of those obtained in two experiments. 

The first point to be established is the dependence of the rate constant on the hydrogen ion concentration. Perchloric acid is a strong acid and is assumed to be completely ionized in water. The constancy or other- 

From the measurements in perchloric acid solutions, where h = [HCIO4], using the mean value in each pair of solutions of the same concentration, we construct table 3. 

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Herczeg, A.C., and Hesslein, R.H. (1984) Determination of hydrogen ion concentration in softwater lakes using carbon dioxide equilibria. Geochim. Cosmochim. Acta 48, 837-845. 

Fels was the first to take advantage of such buffer mixtures. They were frequently employed by SSrensen. In the colori-metrie determination of hydrogen ion concentration they are almost indispensable. We see that the hydrogen or hydroxyl ion concentration always lies in the neighborhood of the dissociation constant of the acid or base used. When the acid and salt concentrations are equal,... 

The best buffer mixtures are obtained by mixing equivalent amounts of acid and salt. The application of buffer mixtures will be taken up later under the discussion of the colorimetric determination of hydrogen ion concentration. 

The transformation range is different for each indicator. Apart from the personal element involved in making observations, the interval depends upon the depth of the liquid layer being observed, the indicator concentration, and the temperature. The influence of indicator concentration especially has never been sufficiently considered. Since this effect is of utmost importance in the colorimetric determination of hydrogen ion concentration as well as in many titrations, it will be discussed thoroughly in the next section. 

It need not be emphasized again that these considerations are of utmost importance in connection with the colorimetric determination of hydrogen ion concentration. The concentration error is most likely to occur when p-nitrophenol is employed as the indicator, appreciably less when phenolphthalein is involved, and least important when the very insoluble thymolphthalein is used, r... 

A second difficulty enters when one of the two forms is insoluble. This must be guarded against, especially in the colorimetric determination of hydrogen ion concentration. The azo dye dimethylamino-azo-benzene (dimethyl yellow) will serve to illustrate this difficulty. Dimethyl yellow is a weak base wdth a pBOH = 10. It is very insoluble and shows a yellow color. The red colored salt, on the other hand, is much more soluble in water. In the equation... 

The influence of neutral salts and proteins on the transformation range will be considered in great detail in connection with the colorimetric determination of hydrogen ion concentration (Chapter Ten). In the same chapter will be reported the results of L. Michaelis and M. Mizutani, who have measured the dissociation constants of the nitro indicators in solutions of differing alcohol concentrations. 

Determination of hydrogen ion concentration with indicator papers. 

Gutstein, M. (1932). Determination of hydrogen-ion concentration in living yeast and bacterial cells. Protoplasma 17, 454—470 (in German). 

Prior to the development of the glass electrode and pH meter, the color indicator application found a wide use for the direct determination of hydrogen-ion concentration. William Mansfield Clark (De Lamur Professor Emeritus of Physiological Chemistry at Johns Hopkins University) spent most of his lifetime investigating organic substances suitable for acid-base indicators. He never accepted the pH meter. In his classic book Oxidation-Reduction Potential of Organic Systems he stated ( ) ... 

In the determination of hydrogen ion concentration in a weak acid solution, use of the quadratic equation can sometimes be avoided using a method known as successive approximation. Consider the example of a 0.0150 M solution of hydrofluoric acid, (HF). The K for HF is 7.10 X 10 . To determine the hydrogen ion concentration in this solution, we construct an equilibrium table and enter the initial concentrations, the expected change in concentrations, and the equilibrium concentrations of aU species ... 

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