Base equilibrium constant

One can write acid-base equilibrium constants for the species in the inner compact layer and ion pair association constants for the outer compact layer. In these constants, the concentration or activity of an ion is related to that in the bulk by a term e p(-erp/kT), where yp is the potential appropriate to the layer [25]. The charge density in both layers is given by the algebraic sum of the ions present per unit area, which is related to the number of ions removed from solution by, for example, a pH titration. If the capacity of the layers can be estimated, one has a relationship between the charge density and potential and thence to the experimentally measurable zeta potential [26]. 

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. 

K. See Equilibrium constant Ka. See Acid equilibrium constant See Base equilibrium constant Kc. See Equilibrium constant Kf. See Formation equilibrium constant Kr See Equilibrium constant K,p. See Solubility product constant K . See Water ion product constant K-electron capture The natural radioactive process in which an inner electron (n = 1) enters the nucleus, converting a proton to a neutron, 514 Kelvin, Lord, 8... 

The acid-base equilibrium constant for the Me residue can be determined by spectroscopic pH titration. An example for the titration is shown in Fig. 2. The electrostatic potential

difference between the apparent pK on the charged surface (pKobs) and that on an intrinsic neutral surface (pK1) by... 

An indication of the nature of the transition state in aromatic substitution is provided by the existence of some extrathermodynamic relationships among rate and acid-base equilibrium constants. Thus a simple linear relationship exists between the logarithms of the relative rates of halogenation of the methylbenzenes and the logarithms of the relative basicities of the hydrocarbons toward HF-BFS (or-complex equilibrium).288 270 A similar relationship with the basicities toward HC1 ( -complex equilibrium) is much less precise. The jr-complex is therefore a poorer model for the substitution transition state than is the [Pg.150]

With reference to a solvent, this term is usually restricted to Brpnsted acids. If the solvent is water, the pH value of the solution is a good measure of the proton-donating ability of the solvent, provided that the concentration of the solute is not too high. For concentrated solutions or for mixtures of solvents, the acidity of the solvent is best indicated by use of an acidity function. See Degree of Dissociation Henderson-Hasselbalch Equation Acid-Base Equilibrium Constants Bronsted Theory Lewis Acid Acidity Function Leveling Effect... 

ACYL-PHOSPHATE INTERMEDIATE ACID-BASE EQUILIBRIUM CONSTANTS DEGREE OF DISSOCIATION HENDERSON-HASSELBALCH EQUATION Acid/base groups in enzymes,... 

A quantitative measure of the degree of dissociation is given by the equilibrium constant for the acid or base. The higher the equilibrium constant is, the greater the percent dissociation of the acid or base. Therefore, a higher equilibrium constant means a stronger acid or base. Equilibrium constants, K and K, are listed for several com-mon weak acids and bases in Table 13.4. 

Acid-base equilibrium constants have been used to calculate the a-values of azoles as substituents on an aromatic ring or on an aliphatic chain. An example of this last case is the determination of ct, values of 1- (acetic acids 740,741, and 721 (Table 11-5) (82KGS264). 

The value of does not depend on the medium composition, and in principle this is the only equilibrium constant needed. However, since activities of substrates and products are often hard to get at, concentration-based equilibrium constants are often used instead. Concentrations can, for example, be expressed as molar ratios (xA, etc.). For each substrate or product, mole ratio and activity can be interconverted using activity coefficients (yA, etc), where aA = yA xA. 

ADCA 7-Amino-3-desacetoxycephalosporanic acid APA 6 Aminopenicillanic acid HPG D-p-Hydroxyphenylglycine HPGA D-p-Hydroxyphenylglycine amide Keq Concentration based equilibrium constant Kth Thermodynamic equilibrium constant... 

Notation for acid and base equilibrium constants Kal refers to the acidic species with the most protons and refers to the basic species with the fewest protons. The subscript a in acid dissociation constants will usually be omitted. 

The definition of pH is pH = —log[H+] (which will be modified to include activity later). Ka is the equilibrium constant for the dissociation of an acid HA + H20 H30+ + A-. Kb is the base hydrolysis constant for the reaction B + H20 BH+ + OH. When either Ka or Kb is large, the acid or base is said to be strong otherwise, the acid or base is weak. Common strong acids and bases are listed in Table 6-2, which you should memorize. The most common weak acids are carboxylic acids (RC02H), and the most common weak bases are amines (R3N ). Carboxylate anions (RC02) are weak bases, and ammonium ions (R3NH+) are weak acids. Metal cations also are weak acids. For a conjugate acid-base pair in water, Ka- Kb = Kw. For polyprotic acids, we denote the successive acid dissociation constants as Kal, K, K, , or just Aj, K2, A"3, . For polybasic species, we denote successive hydrolysis constants Kbi, Kb2, A"h3, . For a diprotic system, the relations between successive acid and base equilibrium constants are Afa Kb2 — Kw and K.a Kbl = A w. For a triprotic system the relations are A al KM = ATW, K.d2 Kb2 = ATW, and Ka2 Kb, = Kw. 

Recall that the relations between acid and base equilibrium constants are... 

The ability to make good estimates of acid-base equilibrium constants is an invaluable aid in thinking about organic reactions and processes. Moreover, experimental workup procedures often require pH control that can be easily understood on the basis of pKa considerations. Thus the concept of acid strength is exceedingly important and should be mastered. 

The acid equilibrium constant KL involves the COOH termination the base equilibrium constant K2 involves the amine termination. At the isoelectric point (pH = (l/2)(pRi pR2) the amino acid is a zwitterion or betaine The proton is detached from the carboxylate end and is attached at the amine end. Dipeptides are formed by the addition of any two amino acids and a loss of a water molecule, for example ... 

Such constants depend not only on temperature but also on the -> ionic strength of the solution, have units of concentration (e.g., molarity) raised to some power, and are related to the activity based equilibrium constant Ka by the expression... 

These two solids will, of course, exhibit different catalytic effects. The equilibrium constant of reaction (XIV) is KAgCiIKAgBT which in water at 25°C equals 500. The tendency for reactions like (XIII) and (XIV) to occur can thus be calculated from known solubility products and stability constants. In the case of solids like oxides or carbonates, one must also take into account the relevant acid-base equilibrium constants because here dissolution can occur if the solution is made sufficiently acid or alkaline. 

The acid-base equilibrium constants of 3-oxy-7-nitrobenzofurazans were determined with the help of UV spectroscopy [1106, 1234], Kinetics of the reaction of methoxydegalogenization and hydrolysis of 4-chloro-7-nitro-2,l,3-benzoxadiazole has been investigated [1106], UV-spectra of some nitrobenzofurazan derivatives are described [1242-1244],... 

Influence of Ionic Strength. It should be noted that eorrections to take aecount of ionic strength as discussed in Section 3.2.1.2 apply not only to the acid-base equilibrium constants but also to the stability constants for complex formation. 

A.2.1 Chemical Exergy of Hydrogen and Carbon Monoxide Derived Using Eugacity-Based Equilibrium Constants... 

Sections 3.3.1 and 4.2.1 dealt with Bronsted acid/base equilibria in which the solvent itself is involved in the chemical reaction as either an acid or a base. This Section describes some examples of solvent effects on proton-transfer (PT) reactions in which the solvent does not intervene directly as a reaction partner. New interest in the investigation of such acid/base equilibria in non-aqueous solvents has been generated by the pioneering work of Barrow et al. [164]. He studied the acid/base reactions between carboxylic acids and amines in tetra- and trichloromethane. A more recent compilation of Bronsted acid/base equilibrium constants, determined in up to twelve dipolar aprotic solvents, demonstrates the appreciable solvent influence on acid ionization constants [264]. For example, the p.Ka value of benzoic acid varies from 4.2 in water, 11.0 in dimethyl sulfoxide, 12.3 in A,A-dimethylformamide, up to 20.7 in acetonitrile, that is by about 16 powers of ten [264]. 

For HA a weak acid the products of the dissociation are hydrogen ion (H" ) and an anion (A ), which is the conjugate base. Equilibrium constants for acids can be written in the following form ... 

McCoy (1993) has considered polymerization reactions that are reversible (i.e., oligomers may depolymerize), and may be either random or proportioned fissions. If the bimolecular kinetic constant and the molar concentration based equilibrium constant K are the same for all steps, and if the cracking reactions... 

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