Solubility acidity constant determination from

Establishment of solid/solution equilibria was followed as a function of time. Resulting equilibrium solutions were filtered through 0.45 pm filters, which might not have been sufficiently effective to retain small colloids. On the other hand, concentrations of dissolved Zr in the equilibrium solutions were determined by complexometry, which wouid not detect colloidal Zr. The solubility data were interpreted by presence of the dominant solution species Zr(OH)j and Zr2(OH) with complexation constants determined from the potentiometric titrations, using solubility constants of Zr(OH)4 as the only fitting variable. However, as can be seen in Figures D-6 to D-9 the experimental data can be equally well fitted by presence of polymeric species, for example by the presence of the two tetramers Zr (OH) and Zr4 (OH) 5. The results were not substantially influenced by NO3 complexation. In most cases, the contribution of NOj complexes represented less than 1% of the total speciation. A maximum of 17% N07 complexes is predicted for the most acid medium in 2 M NaN03. 

The general approach illustrated by Example 18.7 is widely used to determine equilibrium constants for solution reactions. The pH meter in particular can be used to determine acid or base equilibrium constants by measuring the pH of solutions containing known concentrations of weak acids or bases. Specific ion electrodes are readily adapted to the determination of solubility product constants. For example, a chloride ion electrode can be used to find [Cl-] in equilibrium with AgCl(s) and a known [Ag+]. From that information, Ksp of AgCl can be calculated. 

In determinations of sulphurous acid and sulphites, excess of standard 0.05M iodine is diluted with several volumes of water, acidified with hydrochloric or sulphuric acid, and a known volume of the sulphite or sulphurous acid solution is added slowly and with constant stirring from a burette, with the jet close to the surface of the liquid. The excess of iodine is then titrated with standard 0.1M sodium thiosulphate. Solid soluble sulphites are finely powdered and added directly to the iodine solution. Insoluble sulphites (e.g. calcium sulphite) react very slowly, and must be in a very fine state of division. 

A potentiometric method for determination of ionization constants for weak acids and bases in mixed solvents and for determination of solubility product constants in mixed solvents is described. The method utilizes glass electrodes, is rapid and convenient, and gives results in agreement with corresponding values from the literature. After describing the experimental details of the method, we present results of its application to three types of ionization equilibria. These results include a study of the thermodynamics of ionization of acetic acid, benzoic acid, phenol, water, and silver chloride in aqueous mixtures of acetone, tetrahydrofuran, and ethanol. The solvent compositions in these studies were varied from 0 to ca. 70 mass % nonaqueous component, and measurements were made at several temperatures between 10° and 40°C. 

Many water-insoluble drugs are either weak bases or weak acids. There exists an equilibrium of ionized and unionized species for a weak base or a weak acid in an aqueous solution. The pH car affect the equilibrium between ionized and nonionized solute species, and consequently can have an effect on the capacity of micellar solubility. An example of this is the decreased uptake of 4-chlorobenzoic acid by polysorbate 80 micelles observed when the pH is changed from 3 to 4.4 (Collette and Koo, 1975). Another example regarding the effect of SDS micelles orKthefp atenolol, nadolol, midazolam, and nitrazepam is provided by Castro et al. (1998). Apparent acidity constants (p of the drugs were determined potentiometrically or spectrophotometrically in... 

The acidity constant of a given acid in any solvent SH can then be calculated from Eq. (4-15) when its acidity constant in water at infinite dilution, the acidity constant of another acid HB in water and in solvent SH, and the activity term are all known. The values y A 7hb can be obtained from solubilities, partial pressures, distribution coefiicients, etc. The ratio /y can be determined potentiometrically, or from the solubility of salts. The values of. STsh calculated in this way correspond satisfactorily with the measured values. 

The coefficients in equations (26) and (27) for the dissociation of a number of acids and the solubility of calcium carbonate are given in Table A6.5 (Millero, 1979, 1995). The results for carbonic and boric acid are taken from the measurements of Culberson and Pytkowicz (1968). The effect of pressure on the solubility of calcite and aragonite has been determined from the measurements of Ingle (1975). The effect of pressure on the dissociation constants of water, hydrogen sulfate, hydrogen sulfide, ammonia, and hydroffuoric and phosphoric acids have been estimated from molal volume and compressibility data. 

Fini A, de Maria P, Guarnieri A, Varoli L. Acidity constants of sparingly water-soluble drugs from potentiometric determinations in aqueous dimethyl sulfoxide. J Pharm Sci 1987 Jan 76(l) 48-52. 

Gelbach and King [42GEL/K1N] prepared their specimen of Ag2Se04(s) by slow precipitation from 10% silver nitrate and magnesium selenate solutions. The solubility in six solutions of selenic acid in the concentration range from 0.00 to 0.12 M was determined. Equilibrium was approached from under- as well as supersaturation. The solubility in water was found to be 2.42 x 10 M. No solubility product was calculated from the data. This has been done here with log K° = 1.75 for the protonation constant... 

Solutions of barium iodate thermally equilibrated with excess barium iodate monohydrate by stirring approximately one hour in a constant-temperature bath were titrated with 0.01043 N thiosulfate solution after reaction with excess potassium iodide in acid solution. Solubilities in grams per liter calculated from four or more determinations at each temperature were as follows 20°, 3.70 X 10 25°, 4.25 X 10-> 30°, 4.83 X lO" 35°, 5.42 X 10 The increase in solubihty is very nearly linear with increase in temperature. The solubility product constant for temperatures between 20 and 35° can be found from the equation. 

The synthesis of manganese acetate tetra-p-aminophenylporphyrinate (MnAc-TAPhP) chemically immobilized on different polymeric supports was carried out, and its catalytic activity during cholesterol oxidation by molecular oxygen was studied [107]. Soluble porphyrin-containing polymers were obtained by copolymerization of methacrylate or 4-vinylpyridine with the product of interaction of acrylic acid chloride with MnAcTAPhP. Cholesterol oxidation was performed in a 1 1 mixture of ethanol and chloroform. The effective rate constants, / eff, were determined from the initial rate of product formation. 

The measurement of formal potentials allows the determination of the Gibbs free energy of amalgamation (cf Eq. 1.2.27), acidity constants (pATa values) (cf. Eq. 1.2.32), stability constants of complexes (cf. Eq. 1.2.34), solubility constants, and all other equilibrium constants, provided that there is a definite relationship between the activity of the reactants and the activity of the electrochemical active species, and provided that the electrochemical system is reversible. Today, the most frequently applied technique is cyclic voltammetry. The equations derived for the half-wave potentials in dc polarography can also be used when the mid-peak potentials derived from cyclic voltammograms are used instead. Provided that the mechanism of the electrode system is clear and the same as used for the derivation of the equations in dc polarography, and provided that the electfode kinetics is not fully different in differential pulse or square-wave voltammetry, the latter methods can also be used to measure the formal potentials. However, extreme care is advisable to first establish these prerequisites, as otherwise erroneous results will be obtained. 

Physical-chemical data concerning ionic equilibria can be obtained from conductimetric studies. Con-ductimetric measurement has led to the determination of acid and base dissociation constants, stability constants, and solubility product constants. Further details may be found in modern texts of physical chemistry. 

In more efficiently designed and operated sulfur burners such as those used in the paper industry and in the manufacture of sulfuric acid (Shreve, 1944), the sulfur is melted, atomized in compressed air, and burnt in a separate combustion chamber. In these burners gas of a constant composition, 19-20 volume per cent SOa, without any sublimation and with only 0.14% of the sulfur transformed into SOs, can be obtained. Sulfur dioxide is a colorless gas having a characteristic odor, a normal molecular volume of 21.89 1., and a molecular weight of 64.06 g. It is soluble to the extent of 36.4 volumes in one volume of water at 20° C. Its solubility in water decreases from 8.6% by weight at 20° C. to 0.1% at 100° C. At atmospheric pressure SO2 liquefies at —10° C. at 20° C. liquid SO2 exerts a pressure of 3.25 atm. or 40.6 p.s.i. The solubility of sulfur dioxide in water has been determined accurately by Beuschlein and... 

The solubility of HNO3 in sulfuric acid will determine whether the products of reactions (7) to (10) remain in solution or enter the gas phase. The effective Henry s law constant, H, for HNO3 in sulfuric acid as a function of temperature for solutions between 58 wt.% and 87 wt.% has been determined [35]. The data in Ref. [35] have been reanalyzed to correct an error of a factor of the square root of k in one of the equations, and with a steeper dependence of the viscosity (from which the diffusion... 

The analytically pure amino acids required for the measurement of physical properties of amino acids, the determination of amino acids by colorimetric and microbiolo cal methods and the study of the metabolic functions of amino acids, may be prepared by reciystallisation from water, dilute HCl, or an aqueous solution of methanol, ethanol or other alcohol. An amino acid is recrystallised und conditions such as those outlined in Table II until inorganic impurities have been removed, and the value found for a physical property (such as specific rotation or solubility) or a constituent (such as nitrogen) is in close agreement with the standard or theoretical figure. If no standard figure few a physical property is available the product is recrystallized until a constant value is obtained. 

A tenside with a relatively strong lipophilic group and weak hydrophilic group is mainly soluble in oil and preferentially stabilizes a w/o emulsion, and vice versa. This fact led to the development of a standard with which the relative strength or activity of the hydrophilic and lipophilic groups of emulsifiers can be evaluated. It is called the HLB value (hydrophilic-lipophilic balance). It can be determined, e. g., from dielectric constants or from the chromatographic behavior of the surface-active substance. The HLB value of the fatty acid esters of polyhydroxy alcohols can also be calculated as follows (SV =... 

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