Hydrogen ions reaction, ionic strength

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. 

However, the intercepts of log [Fe(II)]/[Ce(IV)] versus time plots deviate from the values expected for the initial concentrations of the reactants. This apparent zero-time oxidation , which is reproducible, is believed to result from a finite quenching time, and the reaction of Fe(ll) with a very reactive Ce(IV) species. Added amounts of Ce(III) and Fe(lII) leave the rate unaffected. At constant ionic strength, k varies inversely with hydrogen-ion concentration in the range 0.05 to 1.00 M for [H" "] > 1.0 M, k increases with increasing In general... 

Oxidation of arsenic(III) by chromate in alkaline medium was studied by Kolt-hoff and Fineman. They found the reaction to be first order with respect to both chromate and arsenic(rir). At pH greater then 9.1 the rate coefficient is independent of the hydrogen-ion concentration. The average value of the rate coefficient at 30° in solutions of pH 9.1 and ionic strength 1.75 was found to be (1.61+0.08) x 10 l.mole sec . ... 

Table 4.9 Changes in the Binding of Hydrogen Ions for the New Reactions in Gluconeogenesis at 298.15 K and 0.25 M Ionic Strength ...

Figure 4.6 Plot of the change in binding of hydrogen ions in the reaction ATP + H20 = ADP + Pj at / = 0, 0.10 and 0.25 M at 298.15 K. The more curved plot is at zero ionic strength. (See Problem 4.5.)...

Figure 9.4 Dependence of the binding of hydrogen ions on the pH at 298.15 K and ionic strength 0.25 M for the following five biochemical half-reactions (starting at the top) ...

These tables can be used to calculate ArG ° and ATH ° at pH 7 and ionic strengths of 0, 0.10, and 0.25 M or at ionic strength 0.25 M and pHs of 5, 6, 7, 8, and 9 for any reaction for which all the reactants are in these tables. They can also be used to calculate standard apparent reduction potentials. The species data can be used to calculate average bindings of hydrogen ions by reactants. Mathematica programs for carrying out these calculations are provided. 

In solutions of ionic strength of approximately 0.25 M, a hydrogen ion dissociates from HATP3- with an acid-base pK of approximately 6.47 [5], where pK is defined as — log10 Keq and Keq is the dissociation reaction equilibrium constant. The equilibrium expression is ... 

In comparisons of rate coefficients measured at different pH values, it is necessary to keep a constant ionic strength by addition of a neutral salt such as NaCl, KC1, NaNOs, or NaC104, as the pH of a buffer system may be altered by a change of ionic strength (secondary salt effect [1]). Furthermore, the catalytic rate coefficient of a hydrogen ion or hydroxide ion catalyzed reaction is dependent on the ionic strength also (primary salt effect [1], see also Vol. 2, p. 337). 

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