Solutions pH calculation

In the absence of diffusion limitations, Co(II) oxidation rate increases with solution pH under wall-jet conditions in the manner similar to the rise in the concentration of CoEn + species as a function of solution pH, calculated from the stability constants of corresponding complexes and the protonation of ethylenediamine [29,36]—their content at pH = 6 is negligible, about 25% at pH = 7, and over 80% at pH = 8 (see Figure 19.11A). From this correlation, a trivial conclusion could be drawn that CoEn "1" species are directly responsible for Co(II) oxidation current, which could be expressed in a simplified form as... 

FIGURE 10.1 Intrinsic exchange rates of several types of labile hydrogen atoms as functions of solution pH calculated based on the data compiled in Dempsey [71]. Reproduced with permission from Kaltashov and Eyles [72],... 

As we shall see for every kind of solution, pH calculations are, as a rule, always possible from a purely mathematical point of view. Indeed, the expressions of equilibria and those of charge and mass balances are always required to provide the same number of equations as the number of unknowns. However, the resulting polynomial equations may be difficult to solve because their order is higher than 2 in the existing unknown. Then numerical calculations may be made. Additionally, they can be performed with pocket calculators. Another way is to make approximations, which greatly simplify the solution of the problem (see below) in Eqs. (5.5) and (5.6), no parameter is characteristic of some particular acid, provided it is strong. The result is that every strongly acidic solution exhibits the same pH value for the same analytical concentration in the above Eqs. (5.1), (5.3), and (5.4), we have not set up... 

This relationship is one form of the Henderson-Hasselbalch equation It is a useful relationship m chemistry and biochemistry One rarely needs to cal culate the pH of a solution—pH is more often mea sured than calculated It is much more common that one needs to know the degree of ionization of an acid at a particular pH and the Henderson-Hasselbalch equation gives that ratio... 

Assay of beryUium metal and beryUium compounds is usuaUy accompHshed by titration. The sample is dissolved in sulfuric acid. Solution pH is adjusted to 8.5 using sodium hydroxide. The beryUium hydroxide precipitate is redissolved by addition of excess sodium fluoride. Liberated hydroxide is titrated with sulfuric acid. The beryUium content of the sample is calculated from the titration volume. Standards containing known beryUium concentrations must be analyzed along with the samples, as complexation of beryUium by fluoride is not quantitative. Titration rate and hold times ate critical therefore use of an automatic titrator is recommended. Other fluotide-complexing elements such as aluminum, sUicon, zirconium, hafnium, uranium, thorium, and rate earth elements must be absent, or must be corrected for if present in smaU amounts. Copper-beryUium and nickel—beryUium aUoys can be analyzed by titration if the beryUium is first separated from copper, nickel, and cobalt by ammonium hydroxide precipitation (15,16). 

Table 5-2. Selected rate constants and half-livese) for some reactions of substituted benzenediazonium ions with buffer solutions (pH 9.00) at 25 °C (rate constants from Virtanen and Kuok-kanen, 1977 half-lives calculated by the present author).

Suppose we are titrating the triprotic acid H P04 with a solution of NaOH. The experimentally determined pH curve is shown in Fig. 11.13. Notice that there are three stoichiometric points (B, D, and F) and three buffer regions (A, C, and E). In pH calculations for these systems, we assume that, as we add the hydroxide solution, initially NaOH reacts completely with the acid to form the diprotic conjugate base... 

A flow chart summarizes the major species in solution and the pH calculations for the four key regions of a weak acid titration curve. 

The starting pH of the solution is calculated using i and the initial molarity of the diprotic acid. We use the standard approach to a weak acid equilibrium ... 

C18-0136. A technician accidentally pours 35 mL of 12 M HCI into the I.O L of buffer solution freshly prepared as described in Problem 18.93. (a) Do a calculation to determine whether the buffer has been ruined, (b) Is it possible to bring the buffer solution back to the original pH calculated in Problem 18.93 If so, what reagent, and how much, must be added to restore the buffer ... 

M tris-HCl buffer solution (pH 7.94) was used as mobile phase. The peak separation obtained with a three column set (G 3000 PW + 2 G5000 PW) is comparable to the peak separation obtained in the present study for the molecular weight range, 120,000 to 3.6 X 10. Peak broadening appeared to be appreciable although no calculations of single-species variance were done. 

Aerosil was converted into the sodium form by treating it with a buffer solution (pH = 8.4) made of sodium hydroxide and sodium hydrogen carbonate solutions, after which it was filtered, washed free of alkali, and dried. This sodium-exchanged aerosil was then suspended in a solution of Ni(en)3(N03)2 prepared by adding the calculated amount of ethylene-diamine to a solution of nickel nitrate. The suspension was agitated for about 30 min and filtered off. The catalyst was then washed and dried at 100°C. 

Figure 2.82 (a) Reflectivity of Cu-on-Si electrode at various potentials in borate buffer solution (pH 8.4). A.B.C and D correspond to potentials indicated in the cyclic voltammogram of Figure 2.81(b). Solid lines represent calculated curves while symbols correspond to experimental data, Open circles, A, -0,12 V open squares, B, -0.80V both y-axes are reflectivity x 10". Filled circles, C, 0.40 V, reflectivity x 10" 3 open diamonds, D, —0.80 V, reflectivity x 10 s. (b) Schematic of multi-layer mode) for Cu-on-Si electrode (not to scale). The oxide film is represented as Cu20. From Melendres et ai (1991). 

At the 50.0% point, half (1.88 mmol H30+) will remain unreacted and only half (7.50 mL titrant) of the titrant solution will be added. From this information, and the original 25.00-mL volume of the solution, we calculate [H30+] and then pH. 

When an acid in solution is exactly neutralized with a base the resulting solution corresponds to a solution of the salt of the acid-base pair. This is a situation which frequently arises in analytical procedures and the calculation of the exact pH of such a solution may be of considerable importance. The neutralization point or end point in an acid-base titration is a particular example (Chapter 5). Salts may in all cases be regarded as strong electrolytes so that a salt AB derived from acid AH and base B will dissociate completely in solution. If the acid and base are strong, no further reaction is likely and the solution pH remains unaffected by the salt. However if either or both acid and base are weak a more complex situation will develop. It is convenient to consider three separate cases, (a) weak acid-strong base, (b) strong acid-weak base and (c) weak acid-weak base. 

Suppose a buffer solution of pH = 2.00 is needed. Suggest a conjugate acid-base pair for this solution, and calculate the ratio of the concentration of conjugate base to acid that is needed to prepare it. 

At the equivalence point, all the weak acid has been converted to its conjugate base. The conjugate base will react with water, so treat it as a weak base solution and calculate the [OH ] using IQ. Finally, calculate the pH of the solution. 

Abstract This chapter first explains the natural flotability of some minerals in the aspect of the crystal structure and demonstates the collectorless flotaiton of some minerals and its dependence on the h and pH of pulp. And then the surface oxidation is analysed eletrochemically and the relations of E to the composition of the solutions are calculated in accordance with Nemst Equation. The E h-pH diagrams of several minerals are obtained. Thereafter, electrochemical determination such as linear potential sweep voltammetry (LPSV) and cyclic voltammetry (CV) and surface analysis of surface oxidation applied to the sulphide minerals are introduced. And recent researches have proved that elemental sulfur is the main hydrophobic entity which causes the collectorless flotability and also revealed the relation of the amount of sulfur formed on the mineral surfaces to the recoveries of minerals, which is always that the higher the concentration of surface sulphur, the quicker the collectorless flotation rate and thus the higher the recovery. 

Similarly, for the system of iron/calcium/phosphate, the percentage distribution of various complexes can also be calculated using solution equilibrium calculations as shown in Fig. 6.26. It follows that depending on solution pH, the dominant complexes is CaPO at pH= 10, whereas CaHP04(aq) and CaH2P04are dominant at pH = 8. 

The extent to which the pH of a solution is buffered against additions or removals of protons is measured by the solution s pH buffer capacity. This is defined as the amount of strong acid or base required to produce unit change in pH. The buffering depends on the transfer of protons between donors and acceptors, i.e. Bronsted acids and bases, which form conjugate acid-base pairs. The pH buffer capacity of a solution is calculated from the buffer capacities of the individual acid-base pairs present. 

The presence of the cation protonated on N-1 cannot account for the fluorescence of aqueous acidic adenine solutions (pH = 2), since the 1-methyl derivative does not fluoresce under the same conditions (Borresen, 1967). It has therefore been suggested that other tautomeric forms of the cation are also present, the fluorescent tautomer probably being protonated on the amino-group with another proton on N-7. Quantum mechanical calculations (Veillard and Pullman, 1963) indicate similar proton affinity for N-1 and N-3, and a lesser one for N-7. There are numerous calculations in the literature on the electronic structure of adenine (see Boyd, 1972, and references quoted therein) and a recent one on N-7-H and N-9-H tautomers protonated on N-1 (Jordan and Sostman, 1972). The N-9-H form is preferred according to hoth MINDO and CNDO/2 calculations. 

Fig. 5. Apparent pH calculated through distributions of Fe(OH)2+/ Fe3+ (blue diamonds) and Fe(0H) Fe(0H)3 (brown squares), versus the -log[H+] computed from the number of protons added to the solution on the acid side, or from the amount of added hydroxide, taking Kw=14, on the base side.

Baciocchi et al43 have reported the existence of the pH-dependent mechanistic dichotomy for the deprotonation of 4-methoxybenzyl alcohol radical cation in aqueous solution. In neutral and acidic solutions the 4-MeOC6H4CH2OH + radical cation undergoes C-H deprotonation, while in basic solution (pH 10), the reaction is initiated by deprotonation of the OH group. DFT calculations were carried out and reveal that the OH induced O-H deprotonation is consistent with the charge controlled reaction, while the C-H deprotonation, observed when the base is HjO, appears to be effected by frontier orbital interactions43. 

Wollast, et al., 1968) at 1 atmosphere, 25°C, demonstrates the inherent stability of this mineral at surface conditions. These experimental studies establish the necessity of an alkaline solution (pH 8) and sili v on-centration in aqueous solution controlled by the presence of amorphous silica (20-150 ppm). Calculations based upon laboratory synthesis data suggest that sepiolite could form in equilibrium with quartz (i.e., 10 ppm... 

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