Acidity constant definition

K is the true value of the acidity constant, which depends only on temperature. Using the definition of pH (Eq. 10.1), Eq. (10.4) becomes... 

For an acid-base couple, the relation is (Fig. 3.29) This allows the definition of the acidity constant of... 

The "salt" or conjugate base, A, is the ionized form of a weak acid. By definition, the dissociation constant of the acid, Ka, is... 

The polar O-H bond of alcohols makes them weak acids. By the Bronsted-Lowry definition, acids are hydrogen ion donors and bases are hydrogen ion acceptors in chemical reactions. Strong acids are 100% ionized in water and weak acids are only partially ionized. Weak acids establish an equilibrium in water between their ionized and unionized forms. This equilibrium and the strength of an acid is described by the acidity constant, Ka. Ka is defined as the concentrations of the ionized forms of the acids (H30+ and A-) divided by the un-ionized form... 

Basicity can also be expressed with acidity constants. With amines, Ka defines the equilibrium in the direction of the ammonium salt ionizing to the free amine and hydronium ion in water. Since this is the opposite of the definition of Kb, small Ka s and large pKa s mean strong basicity. 

The Arrhenius Acid-Base Definition The Acid-Dissociation Constant (KJ Relative Strengths of Acids and Bases... 

Boyle s law The gas law stating that, at constant temperature and amount of gas, the volume occupied by a gas is inversely proportional to the applied (external) pressure V - IP. (144) Bronsted-Lowry acid-base definition A model of acid-base behavior based on proton transfer, in which an acid and a base are defined, respectively, as species that donate and accept a proton. (587) buffer (See acid-base buffer.)... 

The acidity constant, K, is a measure of the acidic strength of a compound. The pKg is by definition -log Kg. As the strength of an acid increases, its Kg increases and its pKg decreases. For example, CjHj in (b) has a larger pKg than water. Therefore it is a weaker acid than water. 

Knowledge Required (1) The interpretation of acid equilibrium constants, K. (2) Meaning of terms associated with weak and strong acids and bases. (3) Brpnsted-Lowry acid-base definition. 

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. 

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