Hydrogen ion concentration, effect

Hydrogen-ion concentration effect on enzyme kinetics, 292, 327 on phosphorylase action, 355 mutarotation measurement by, 52... 

A similar hydrogen ion concentration effect is observed with animal phosphorylase and glycogen. The ratio of concentration of inorganic phosphate to glucose-l-phosphate, reached from either side, is 5.7 at pH... 

Gladysheva, V. P. and Shatalov, A. Ya., Effect of Hydrogen-ion Concentration on the Performance of Differentially Aerated Couples , Izv. Vysshikh. Uchebn. Zavedenii, Khim. i Khim. Tekhnoi., 9, 48 (1966) C.A., 65, 5002a... 

The effects of concentration, velocity and temperature are complex and it will become evident that these factors can frequently outweigh the thermodynamic and kinetic considerations detailed in Section 1.4. Thus it has been demonstrated in Chapter 1 that an increase in hydrogen ion concentration will raise the redox potential of the aqueous solution with a consequent increase in rate. On the other hand, an increase in the rate of the cathodic process may cause a decrease in rate when the metal shows an active/passive transition. However, in complex environmental situations these considerations do not always apply, particularly when the metals are subjected to certain conditions of high velocity and temperature. 

This ease with which we can control and vary the concentrations of H+(aq) and OH (aq) would be only a curiosity but for one fact. The ions H+(aq) and OH (aq) take part in many important reactions that occur in aqueous solution. Thus, if H+(aq) is a reactant or a product in a reaction, the variation of the concentration of hydrogen ion by a factor of 1012 can have an enormous effect. At equilibrium such a change causes reaction to occur, altering the concentrations of all of the other reactants and products until the equilibrium law relation again equals the equilibrium constant. Furthermore, there are many reactions for which either the hydrogen ion or the hydroxide ion is a catalyst. An example was discussed in Chapter 8, the catalysis of the decomposition of formic acid by sulfuric acid. Formic acid is reasonably stable until the hydrogen ion concentration is raised, then the rate of the decomposition reaction becomes very rapid. 

The acidity of a solution has pronounced effects on many chemical reactions. It is therefore important to be able to learn and control the hydrogen ion concentration. This control is obtained through application of the Equilibrium Law. Common types of calculation, based on this law, are those needed to determine KA from experimental data and those using KA to find [H+], We will illustrate both of these types, using benzoic acid, QH6COOH, as an example. 

The industrial preparation of bromine takes advantage of this effect of hydrogen ion concentration on the direction of the spontaneous re-... 

This enables us to calculate the effect of change in the ratio [Mn04 ]/[Mn2 + ] at any hydrogen ion concentration, other factors being maintained constant. In this system, however, difficulties are experienced in the calculation owing to the fact that the reduction products of the permanganate ion vary at different hydrogen ion concentrations. In other cases no such difficulties arise, and the calculation may be employed with confidence. Thus in the reaction ... 

In some cases the use of nitrosylsulfuric acid may be avoided if 1-naphthalenesul-fonic acid is added to moderately concentrated sulfuric acid (20-60%). This greatly reduces the evolution of nitrous fumes compared with a solution of pure sulfuric acid of the same hydrogen ion concentration. It has not yet been investigated whether the phenomenon is due to the formation of an ion pair, [C10H7 —SO NO+], or whether it is simply a solubility effect. In any case, the total acidity range of 4-12 m has thereby become available for diazotization technically crude sulfonation mixtures are used after dilution with water, for example, a solution of total acidity 4 m, of which 2.7 m is due to sulfuric acid. A further advantage of the method lies in the stabilizing effect of the naphthalenesulfonic acid on the diazonium compounds formed (see Sec. 2.3). 

In a further study, Brubaker et have reported on the effects of the addition of chloride ion to the sulphate exchange system at virtually constant ionic strength (3.68 M sulphate and hydrogen-ion concentrations. For the concentration ratio [C1 ]/[T1(III)] of 9.2x10" to 9.5 at 24.9 °C results analogous to the effect observed in perchlorate media were obtained. The minimum in the rate corresponded to a ratio of 2.5. Results were also presented for the conditions, constant [CI ] and variable [804 ] and [If"] ( = 3.68 M). Brubaker et al have suggested that the exchange paths most likely to occur in sulphate media are... 

Habib and Hunt have continued the study of this reaction, obtaining further data with special reference to the effects of ionic strength, sulphate and hydrogen-ion concentrations. From data obtained on the dependence of the rate on the [H ] at various temperatures, values of the kinetic parameters differing slightly from those above have been obtained. Values of AFff and and AS and AS2 (at n = 1.0 M) obtained were 11.8, 5.3 kcal.mole and —17 and —31 cal.deg mole respectively. The value of 2 was estimated as 6.7 x 10 1. mole sec at 18 °C, n — 1.0 Af. 

Interest has been shown by several groups on the effect of solvent and of added anions upon the oxidation of alcohols. The oxidation of isopropanol proceeds 2500 times faster in 86.5 % acetic acid than in water at the same hydrogen ion concentration . The kinetics and primary kinetic isotope effect are essentially the same as in water. Addition of chloride ion strongly inhibits the oxidation and the spectrum of chromic acid is modified. The effect of chloride ion was rationalised in terms of the equilibrium,... 

A basic defect of these ideas is their failure to provide an explanation of the substantial effects of sofution composition, in particular the pH value, on the rate of the electrochemical reaction. Since hydrogen ions are not involved in the recombination step, the rate of this step according to Eq. (15.12) should not depend on solution pH. Yet in many cases the rate of hydrogen evolution at constant potential is proportional to the hydrogen ion concentration in solution. 

---