Concentrations and pH

Due to the low volume of solution used in incipient wetness impregnation, the concentration of the precursor in water is often high and sometimes close to the limit of solubility (which depends much on the counterion chosen and on the presence of ligands surrounding the metal ion). 

For values higher than 0.5 mol 1 , activities should be used instead of concentrations to predict the evolution of reactions, because the behavior of ions is influenced by that of the surrounding charged species (including coimpregnants) and the ionic strength acts on adsorption equilibria [44, 52, 53]. High concentrations also lead to an increase of the solution viscosity (Section 4.2). 

It is also possible to prepare catalysts by contacting the support with a suspension in which the precursor is not totally dissolved ( slurry or solvent-assisted spreading ) [54, 55). The equihbrium of dissolution is shifted by the adsorption of the precursor on the support surface, which depletes progressively the Kquid phase from the dissolved ions. Molybdenum-containing catalysts have been prepared from M0O3 by this method, with high yields in metal deposition [55]. Thanks to their viscosity, slurries are also convenient to impregnate foams [56]. 

It is finally recalled here that gases may be dissolved in the impregnation solution. Dissolved oxygen can cause the oxidation of air-sensitive complexes, possibly leading to less-soluble species [57]. Carbon dioxide contributes to the deposition of carbonate ions onto the support [58]. Upon NH3 dissolution (Section 4.2.1), the solution pH may change and pH-related reactions of precipitation or complexation occur. 

The pH is an important parameter in the impregnation process and its influence on the liquid and solid parts of the interface has been described in Chapters 2 and 3. The impregnation solution consists of a mixture of acidic and basic species, whose initial concentrations have been fixed to meet several constraints (mainly the active phase content and its distribution in the pores) and that are subjected to various pH-dependent and interrelated reactions of association or dissociation till equilibrium is reached. On the solid side, the pH rules the sign of the global surface charge and the number of charged sites, and it affects the dissolution of the oxide support both thermodynamically and kinetically. 

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Dg remains constant over a wide range of resin to liquid ratios. In a relatively short time, by simple equilibration of small known amounts of resin and solution followed by analysis of the phases, the distribution of solutes may be followed under many different sets of experimental conditions. Variables requiring investigation include the capacity and percent cross-linkage of resin, the type of resin itself, the temperature, and the concentration and pH of electrolyte in the equilibrating solution. 

Operation nd Control. Control of chromium chromate conversion coating baths is accompHshed by controlling chromium concentration and pH. The quaHty of the conversion coating is sensitive to aluminum accumulations in the coating bath as well as to rinse water purity. Sulfate contamination is a particular problem. 

There are four processes for industrial production of ahyl alcohol. One is alkaline hydrolysis of ahyl chloride (1). In this process, the amount of ahyl chloride, 20 wt % aqueous NaOH solution, water, and steam are controhed as they are added to the reactor and the hydrolysis is carried out at 150 °C, 1.4 MPa (203 psi) and pH 10—12. Under these conditions, conversion of ahyl chloride is 97—98%, and ahyl alcohol is selectively produced in 92—93% yield. The main by-products are diahyl ether and a small amount of high boiling point substance. The alkaU concentration and pH value are important factors. At high alkah concentrations, the amount of by-product, diahyl ether, increases and at low concentrations, conversion of ahyl chloride does not increase. 

The onset of action is fast (within 60 seconds) for the intravenous anesthetic agents and somewhat slower for inhalation and local anesthetics. The induction time for inhalation agents is a function of the equiUbrium estabUshed between the alveolar concentration relative to the inspired concentration of the gas. Onset of anesthesia can be enhanced by increasing the inspired concentration to approximately twice the desired alveolar concentration, then reducing the concentration once induction is achieved (3). The onset of local anesthetic action is influenced by the site, route, dosage (volume and concentration), and pH at the injection site. 

Electroplating. Aluminum can be electroplated by the electrolytic reduction of cryoHte, which is trisodium aluminum hexafluoride [13775-53-6] Na AlE, containing alumina. Brass (see COPPERALLOYS) can be electroplated from aqueous cyanide solutions which contain cyano complexes of zinc(II) and copper(I). The soft CN stabilizes the copper as copper(I) and the two cyano complexes have comparable potentials. Without CN the potentials of aqueous zinc(II) and copper(I), as weU as those of zinc(II) and copper(II), are over one volt apart thus only the copper plates out. Careful control of concentration and pH also enables brass to be deposited from solutions of citrate and tartrate. The noble metals are often plated from solutions in which coordination compounds help provide fine, even deposits (see Electroplating). 

Product recoveiy from reversed micellar solutions can often be attained by simple back extrac tion, by contacting with an aqueous solution having salt concentration and pH that disfavors protein solu-bihzation, but this is not always a reliable method. Addition of cosolvents such as ethyl acetate or alcohols can lead to a disruption of the micelles and expulsion of the protein species, but this may also lead to protein denaturation. These additives must be removed by distillation, for example, to enable reconstitution of the micellar phase. Temperature increases can similarly lead to product release as a concentrated aqueous solution. Removal of the water from the reversed micelles by molecular sieves or sihca gel has also been found to cause a precipitation of the protein from the organic phase. 

In addition to temperature and flow rate, the retention and selectivity in reversed phase are controlled by (i) the concentration and type of organic modifier and (ii) the type, concentration and pH of the buffer. 

Further, for studying the role of pH and salt concentrations on bulk-electrostatic and non-bulk electrostatic contributions the same approach was made to experiments on the influence of the alcohols mentioned above on the oxygen affinity at various KC1 concentrations and pH-values 144,146). The results obtained indicate that at a low alcohol concentration the bulk-electrostatic contributions are dominant and that with increasing size of the alkyl group, alcohol and KC1 concentration, the nonbulk electrostatic, hydrophobic contributions increase. Recent results of kinetic measurements of 02 release show that cosolvents such as alcohols and formamide influence mainly the allosteric parameter L, i.e. -the equilibrium between T and R conformation and that the separation of the alcohol effects into bulk-electrostatic and hydrophobic (non-bulk electrostatic) contributions is justified. 

In either case, the ratio nHBlnB- changes. This in turn changes the H+ ion concentration and pH of the buffer. The effect ordinarily is small, as illustrated in Example 14.4. 

Hydronium ion, 187 concentration calculation, 192 concentration and pH, 190 model, 186 Hydroquinone, 345 Hydrosphere, 437 composition, 439 Hydroxide ion, 106, 180 Hydroxides of lhird row, 371 Hydroxylamine, 251 Hydroxyl group, 329 Hypobromiie ion, 422 Hypochlorite ion, 361 Hypochlorous acid, structure, 359 Hypophosphorous acid, 372 Hypothesis, Avogadro s, 25, 52... 

For each run, calculate and plot the cell biomass concentration, glucose concentration, ethanol concentration, and pH as a function of time. Identify the major phases in batch fermentation lag, exponential, stationary and death. 

The complexation of Pu(IV) with carbonate ions is investigated by solubility measurements of 238Pu02 in neutral to alkaline solutions containing sodium carbonate and bicarbonate. The total concentration of carbonate ions and pH are varied at the constant ionic strength (I = 1.0), in which the initial pH values are adjusted by altering the ratio of carbonate to bicarbonate ions. The oxidation state of dissolved species in equilibrium solutions are determined by absorption spectrophotometry and differential pulse polarography. The most stable oxidation state of Pu in carbonate solutions is found to be Pu(IV), which is present as hydroxocarbonate or carbonate species. The formation constants of these complexes are calculated on the basis of solubility data which are determined to be a function of two variable parameters the carbonate concentration and pH. The hydrolysis reactions of Pu(IV) in the present experimental system assessed by using the literature data are taken into account for calculation of the carbonate complexation. 

The present study is conducted under consideration of thus mentioned difficulties. The solubility measurement is applied to the present investigation, selecting the pH range 6 v 12 in which the carbonate concentration can be maintained greater than 5xl0 6 M/l. The carbonate concentration and pH of experimental solutions, both being mutually dependent in a given solution, are taken into account as two variable parameters in the present experiment and hence the final evaluation of formation constants is based on three dimensional functions. For calculation purpose, the hydrolysis constants of Pu(IV) are taken from the literature (18). In order to differentiate the influence of hydrolysis reactions on the carbonate complexation so far as possible, the calculation is based on the solubilities from solutions of carbonate concentration > 10-1 M/l and pH > 8. 

Successful and reproducible preparation of highly dispersed catalysts crucially depends on the state of the carrier surface and on the concentration and pH of the impregnating solution. It is an art and a science for which several goodbooks and reviews exist.1 5... 

The capacity of a buffer is determined by its concentration and pH. A more concentrated buffer can react with more added acid or base than can a less concentrated one. A buffer solution is generally most effective in the range... 

The biosorption capacity of heavy metals increased with initial metal concentration and pH. 

The latter reaction displayed an induction period independent of reactant concentrations and pH. The initial decompositions may be... 

The composition of the solution depends on concentrations and pH value. In highly diluted solutions, mainly monomeric and dimeric species are present (Doesburg et ciL, 1999). 

Therefore, it is likely that Ag-rich electrum and large amounts of sulfide minerals including argentite could precipitate due to CO2 loss and pH increase under low /sj and /02 conditions. Therefore, this mechanism (boiling and gas loss from the hydrothermal solution with different /sj, /o2> CO2 concentration and pH) could explain why the Ag content of electrum correlates with Ag/Au total production ratio (Fig. 1.124). 

It is thought from this reaction, that Au-rich electrum precipitates from ore fluids with high Cl concentration and low pH. Therefore, it is considered that different Cl concentration and pH are important factors causing different relationship between Ag content of electrum and Ag/Au total production ratio of Kuroko deposits and epithermal vein-type deposits. 

The most widely employed transition metal oxidants for alcohols are based on Cr(VI). The specific reagents are generally prepared from chromic trioxide, Cr03, or a dichromate salt, [Cr207]2-. The form of Cr(VI) in aqueous solution depends upon concentration and pH the pKx and pK2 of H2Cr04 are 0.74 and 6.49, respectively. In dilute solution, the monomeric acid chromate ion [HCr03] is the main species present as concentration increases, the dichromate ion dominates. 

Electrophoretic separations occur in electrolytes. The type, composition, pH, concentration, viscosity, and temperature of the electrolytes are all crucial parameters for separation optimization. The composition of the electrolyte determines its conductivity, buffer capacity, and ion mobility and also affects the physical nature of a fused silica surface. The general requirements for good electrolytes are listed in Table 1. Due to the complex effects of the type, concentration, and pH of the separation media buffer, conditions should be optimized for each particular separation problem. 

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