Hydrogen Ion Concentration pH

The most frequent technique for reducing the impact of moderate acid or alkali production during growth on media is through incorporation of 

As noted by Zoecklein et al. (1995), the pH of the must and wine establishes whether microbes will grow, which species (or strains) will grow, their rate of growth, and the concentration of sensorially important me- 

Hydrogen ion concentration plays a major role in the activity of various antimicrobial agents used in winemaking. As previously discussed and as seen in Figs 1.8, the percentage of molecular sulfur dioxide, increases with decreasing pH. This relationship also applies in the cases of sorbic and benzoic acids. 

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The role that acid and base catalysts play can be quantitatively studied by kinetic techniques. It is possible to recognize several distinct types of catalysis by acids and bases. The term specie acid catalysis is used when the reaction rate is dependent on the equilibrium for protonation of the reactant. This type of catalysis is independent of the concentration and specific structure of the various proton donors present in solution. Specific acid catalysis is governed by the hydrogen-ion concentration (pH) of the solution. For example, for a series of reactions in an aqueous buffer system, flie rate of flie reaction would be a fimetion of the pH, but not of the concentration or identity of the acidic and basic components of the buffer. The kinetic expression for any such reaction will include a term for hydrogen-ion concentration, [H+]. The term general acid catalysis is used when the nature and concentration of proton donors present in solution affect the reaction rate. The kinetic expression for such a reaction will include a term for each of the potential proton donors that acts as a catalyst. The terms specific base catalysis and general base catalysis apply in the same way to base-catalyzed reactions. 

S. Dikstein and A. Zlotogorsky, Skin surface hydrogen ion concentration (pH), in Cutaneous Investigation in Health and Disease — Non-Invasive Methods and Instrumentation (J.L. Leveque, ed.), pp. 59-62. Marcel Dekker, New York (1989). 

Stability constants, from which AG° values are calculated, provide a direct measure of the extent of complexing in solution, and these values have been used to determine cation selectivity by macrocyclic compounds. Several of the methods commonly used to determine log K values cannot be used with many of these systems. Thus, procedures based on change in hydrogen ion concentration (pH titration, hydrogen electrode, etc.) cannot be used in those cases where the ligand is uncharged and its concentration is not pH dependent. Spectral methods generally have not been used because of the usual lack of favorable absorption characteristics by the compounds, cations or cation-complexes in the cases studied. 

Hydrogen ion concentration (pH) was the second criterion by which growth of the bacilli was established. Sulfuric acid is a natural metabolic by-product of sulfur oxidation by the acidophillic Thiobacillus thiooxidans (5). As sulfur is used, acid is built-up in the medium thus lowering the pH. Studies in this laboratory have shown that the bacteria grow well in a pH as low as 0.5. 

Treated papers should maintain at a pH in the range 7 and 8.5. The pH should not be higher than 8.5 to prevent alkaline hydrolysis of cellulose. The acidity or alkalinity may be determined as the amount of water-soluble acidity or as the hydrogen ion concentration (pH) of the paper extract. The pH is more indicative of the stability of paper than is the total acidity. The pH can be determined by either a hot or cold extraction method. In the cold extraction method,... 

Hydrogen ion concentration (pH) has particular relevance to drug absorption since approximately 75 percent of all clinically utilized drugs can behave as either weak... 

Like most other catalysts, enzymes can be poisoned if the active sites become clogged by an unwanted molecule. Inorganic metal catalysts are easily spoiled by hydrogen sulfide (H2S) or arsenic, whereas enzymes are particularly vulnerable to changes in hydrogen ion concentrations (pH) and temperature. Enzymes work best at temperatures around 37 °C (body temperature) and at a pH around 7 (neutral), although the digestive enzymes in the stomach work at a much lower pH. 

Some individuals have advocated reporting of acidity of body fluids in terms of hydrogen ion concentration instead of pH. Their rationale is that pH is a measure of the chemical potential of hydrogen ions rather than a measure of the concentration of the ions,. Because chemical potential is a function of the activity coefficient, which is not known with certainty, the antilog of pH cannot be assumed to equal the hydrogen ion concentration. pH values should be treated as primary variables and reported as measured. 

Hydrolysis of meperidine hydrochloride in dilute hydrochloric acid is a specific hydronium ion catalyzed reaction which is first order with respect to hydrogen ion concentration. A positive, primary salt effect was noted in dilute acid solution. The hydrolysis of the protonated form of meperidine hydrochloride was found to be first order with respect to meperidine hydrochloride over a wide range of hydrogen ion concentration (pH 1-7) A catalytic effect with respect to meperidine hydrolysis was exhibited by di-hydrogen phosphate ion, the only phosphate ion studied in the investigation, and the possibility of similar effects with respect to other buffer systems should be recognized. The rate of hydrolysis was found to be very slow in the pH range of 3.5 to 5 with maximum stability at pH U.01. The calculated half-life for meperidine hydrochloride at pH U.9 is 23.8 years at 25 °C. 

Discuss how you might modify the logarithmic concentration diagram so that it shows the pH in terms of the hydrogen ion activity ah-instead of the hydrogen ion concentration (pH = — log Ah instead of pH = — log Ch ). Be specific in your discussion and show what the difficulties might be. 

The pH scale (Figure 3.16) conveniently expresses hydrogen ion concentration. pH is defined as the negative logarithm of the concentration of hydrogen ions ... 

Release of a proton in buffered solution - A proton is released in some hydrolysis reactions (see Figure 3.7), so hydrogen ion concentration (pH) influences the reaction. 

At low metal ion concentrations (10 mole/liter) and high hydrogen ion concentrations (pH, 1.00), the ionic equilibria involving hydroxyla-tion of the ion have been studied by /3-diketone extraction techniques... 

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