Variation of pH Value

A pH increase from 6.85 to 7.05 results in a change in copper concentration of 55 pg L 1 in river water in contact with sediment containing 55 mg kg  

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Variation of pH value Variation of the ternary solvent mixture... 

Test D Variation of pH value. Seven samples were prepared according to the standard operational procedure, but the pH value was varied by addition ofNa2C03 or HCl. 

Figure 8.10 Variation of pH value after cathodic charging (-500mAg for 12h) of AC electrodes in 0.5 mol 1 Na2S04 solutions where the initial pH was adjusted by addition of 1 mol 1 HjSO or 1 mol h NaOH. (Adapted from Ref. [85].)...

It is also important to state the conditions at which the pFe is determined, as the value will change with the conditions (54). Fig. 4 shows an example of how the pFe value can vary over a range of pH values. This variation is due to the inclusion of a value known as the Ringbom coefficient in the determination of pFe values. The Ringbom coefficient, a, is determined from the mass balance equation as shown below for the ligand Ringbom coefficient. 

Using linear regression, it is possible to estimate the protonation constants of the Fe(II) complexes of siderophore complexes where the redox potentials have been measured over a range of pH values (59). This also explains the variation in reversibility of reduction as the pH changes, as the stability of the ferro-siderophore complex is much lower than the ferric complex, and the increased lability of ligand exchange and increased binding site competition from H+ may result in dissociation of the complex before the iron center can be reoxidized. 

P=f(Xp. pH). As described above, the magnitude of P is inexorably linked to the variations of x with pH and adsorption density. However, the response of x (and P) to T and pH varies among hydrous oxides. For example, Figure 9a shows the instantaneous (isotherm) proton coefficient (xp) "zones" determined for Cd ion adsorption onto (am)Fe20o O, a-A O and oc-TiC. The zones are defined by the calculated proton coefficients determined for a range of pH values and adsorption density. The "thickness" of each zone gives a qualitative comparison of the pH dependency of Xp at each adsorption... 

Potentiometric measurements give log(3/ values which are correct to within 10% but the relative accuracy is difficult to assess due to the successive, repetitive nature of the experiments. Probably the most significant source of error, as we have stated, is the variation of pH with time. At tracer concentrations the enthalpy AH0 can be determined only by the temperature differential method. However, the temperature differential method is not as precise as the calorimetric one. The enthalpy of formation for each complex is computed with the assumption that ACp is constant over the temperature range and that the range of error corresponds to 10%. 

Expected Range of pH Values. Changes in solution pH in rock-water systems may result from two primary causes. The first cause is due to changes in equilibrium constants with variation in temperature and pressure. For example, the neutral pH of pure water changes from 7.00 at 20°C to approximately 5.6 at 200°C and 300 bars pressure due to changes in the value of the dissociation constant for water. Precipitation, dissolution, oxidation, or reduction of phases with consumption or generation of hydrogen ion is the second primary cause of pH variation. 

E. Bosch, S. Espinosa, and M. Roses, Retention of ionizable compounds on high-performance liquid chromatography III. Variation of pK values of acids and pH values of buffers in acetonitrile-water mobile phases,/. Chromatogr. A 824 (1998), 137-146. 

Variation of pH from 7.0 to 6.1 resulted in little change qualitatively, although measured values were slightly higher. A single run at... 

The first dissociation constant of the sulfonephthalein is very large so that the hydrolysis of the HI" ions may be neglected. If we add to pure water an indicator solution for which the ratio [HI-]/[I 3 and the total amount of indicator are known, we should find that the ratio has changed due to the variation of pH with dilution. The [HI ] value diminishes with dilution and []I 3 increases if the indicator mixture has an acid reaction. 

The set of equations are solved with relevant boundary conditions, such as C(m)s at the outside surface of the diffusion layer, x = d, are equal to the values in the bulk solution in equibrium. Since the equations cannot be solved analytically, numerical solution was made by calculus of finite differences Gattrell et al. treated the problem more rigorously, and recently published the results. Figure 2 shows the variation of pH at the electrode surface with the concentration of the electrolyte HCO f the pH values are given for two different thicknesses of the diffusion layer and two constant current electrolysis at 5 and 15 niAcm ... 

References [180-182] report the changes in pH in a fresh titania dispersion at natural pH in water and in 0.005 M NaCl. A constant value was established in about 10 hours. The potential was studied as a function of exposure time (1-14 days) in [169]. The variation of pH with time on addition of base to titania is reported in [183]. 

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