CHEMICAL EQUILIBRIUM III (Lab #4) pH OF SOLUTIONS and IONIZATION CONSTANTS OF WEAK ACIDS AND BASES Los Angeles Trade-Tech College - CHEMISTRY 102 LABORATORY pH is a mathematical way of expressing the hydrogen ion concentration of solutions (the acidity or the basicit is as defined by the Arrhenius theory for acids and bases). It is defined as... = - log [H3O+] {the logarithm is to the base 10} antilog (pH) = 10-PH pH [H3O+] = By definition.... pOH =-log [OH-] and pH + pOH = 14 For a weak acid of the type... HXH* + X The mathematical expression of the equilibrium is written as... K = [H*][X] [HX] For a weak base of the type... MOH The mathematical expression Kb = M + OH- for the equilibrium is written as... [M'][OH] [MOH]