Effect on pH

The possible consequences of a drop in pH are manifold. The pH greatly affects the mechanism of the Maillard reaction itself (see Chapter 2), it affects microbial activity, and it may cause polymeric material, particularly proteins, to lose solubility and thus alter texture. 

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A more recently introduced product is polyalurninum—siHcate—sulfate or PASS, made by Handy Chemical of Quebec. It is said to be more effective than alum in cold water, have only a slight effect on pH, and leave less residual aluminum in the water. It is sold as a solution (8). 

In sodium chloride solutions the ion transport number for Na+ is about 0.4 compared to about 0.6 for CU. Thus a CX membrane would be expected to polarize at lower current densities than an AX membrane. Careful measurements show that CX membranes do polarize at lower current densities however, the effects on pH are not as significant as those found when AX membranes polarize. Such differences ia behavior have beea satisfactorily explaiaed as resultiag from catalysis of water dissociatioa by weaMy basic groups ia the AX membrane surfaces and/or by weaMy acidic organic compounds absorbed on such surfaces (5). 

We have seen how to estimate the pH of a solution of a weak acid or base (Chapter 10), but suppose that a salt of the acid or base is also present. How does that salt affect the pH of the solution Suppose we have a dilute hydrochloric acid solution and add to it appreciable concentrations of the conjugate base, the Cl- ion, as sodium chloride. Because the acid is strong, its conjugate base is extremely weak and so has no measurable effect on pH. The pH of 0.10 M HCl(aq) is about 1.0, even after 0.10 mol NaCl has been added to a liter of the solution. Now suppose instead that the solution contains acetic acid to which sodium acetate has been added (the acetate ion, CH jC()2, is the conjugate base of CH COOH). Because the conjugate base of a weak acid is a base, we can predict that adding acetate ions (as sodium acetate) to a solution of acetic acid will increase the pH of the solution. Similarly, suppose we have a solution of ammonia and add ammonium chloride to it. The... 

Fig. 15.1. Calculated effects on pH of reacting hydrochloric acid into a 0.2 molal NaCl solution and a 0.1 molal Na2CC>3 solution, as functions of the amount of HC1 added. The two plateaus on the second curve represent the buffering reactions between COJ- and HCOJ, and between HCO3 and C02(aq).

Fig. 15.6. Effects on pH (top) and C02 fugacity (bottom) of reacting HC1 into a fluid not in contact with calcite (fine lines) and with the same fluid when it maintains equilibrium with calcite over the reaction path (bold lines).

Fig. 15.10. Calculated effects on pH of reacting sodium hydroxide into an initially acidic solution that is either closed to mass transfer (fine line) or in equilibrium with atmospheric C02 (bold line).

The second proton that can dissociate has a negligible effect on pH (Kti very small)... 

Chirife and Buera (1996) likened the solute-specific effect on aw to that on pH. The solute effect on pH has not precluded the widespread usage of pH in food preservation. Rather, it is important to understand and quantify its limitations, but not discontinue its usage. For example, it is important to quantify the specific inhibitory effects of various food grade acids and to establish safe pH limits corresponding to the less inhibitory ones rather than... 

First, the effect of SL is immediately apparent. Low SLs can be employed in the laboratory to minimize pH shifts. At high SLs, oxides exhibit a dramatic effect on pH. In fact, this plot predicts that the final pH of DIs is almost always at the PZC of the oxide, unless the starting solutions are extremely acidic or basic [11]. Alternatively, in DI the hydroxyl groups on the oxide surface far outnumber the protons or hydroxide ions initially in solution, and the surface never becomes significantly charged. 

In the absence of precipitation or effects on pH or osmolality, the maximum concentration of the main mutagenicity study is a concentration that reduces survival to approximately 20% of the control value. 

In this section, you compared strong and weak acids and bases using your understanding of chemical equilibrium, and you solved problems involving their concentrations and pH. Then you considered the effect on pH of buffer solutions solutions that contain a mixture of acid ions and base ions. In the next section, you will compare pH changes that occur when solutions of acids and bases with different strengths react together. 

Alberty analyzed the anion effect on pH-rate data. He first considered a one-substrate, one-product enzyme-catalyzed reaction in which all binding interactions were rapid equilibrium phenomena. He obtained rate expressions for effects on F ax and thereby demonstrating how an anion might alter a pH-rate profile. He also considered how anions may act as competitive inhibitors. The effect of anions on alcohol dehydrogenase has also been investigated. Chloride ions appear to affect the on- and off-rate constants for NAD and NADH binding. See also pH Studies Activation Optimum pH... 

The specific assay conditions have altered or modified the protein(s) or system such that the experimentally observed pHopt is not the physiological pHopt. For example, some component may be missing from the reaction mixture, a component that is present in the reaction mixture (and not present in physiological contexts) has altered the system, a nonphysiological ionic strength or temperature has altered the pHopt, etc. See Anion Effects on pH-Rate Data... 

Although neutralized wastewater falls a clear IS ft before entering the settlement basin, and settled effluent passed through a straw bale filter, operating data reveal no evidence of any effect on pH of carbon dioxide stripping in the fall, or of straw bale filtration on metals concentrations.14... 

In most solutions of weak acids, the concentration of hydronium ions is so high that [H30+] > 1CT6 (that is, pH < 6). Under these conditions, Xw/[H30+] < 10-8 and we can ignore this term in both the numerator and the denominator of Eq. 19. The expression for fCa simplifies to the familiar one we use when the autoprotolysis of water has an insignificant effect on pH (Section 10.10) ... 

The pH of a solution at the stoichiometric point of an acid-base titration depends on the properties of the salt formed in the neutralization reaction. At the stoichiometric point of the titration of formic acid, HCOOH (1), with sodium hydroxide, the solution consists of sodium formate, NaHC02, and water. Formate ion, HC02 (2), is a base, and the Na+ ions have virtually no effect on pH so overall the solution is basic, even though the acid has been completely neutralized. 

Fig. 5.8. Effect on pH of lofting (convecting) tropospheric chemistries to higher altitudes...

Aldehydes, introduction in polysaccharides, 189-190 Aligned fiber moderators, flow rate, 346r Amine functions, effect on pH sensitivity of poly(ortho esters), 176-178 Aminobenzoate esters, correlations of partition coefficients for solvent pairs, 62,63/... 

Table VII Aging Tests on Washed Paper, Effect on pH, Foldur Kraft Paper...

Figure 7. Effect on pH of Foldur Kraft paper after chemical feeder...

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