species present (H O + , F – and HF) in the solution and its pH. Table . The Values of the Ionization Constant of Some Weak Bases at K Base K b Dimethylamine, (CH ) NH . × – Triethylamine, (C H ) N .
× – Ammonia, NH or NH OH . × – Quinine, (A plant product) . × – Pyridine, C H N . × – Aniline, C H NH .
× – Urea, CO (NH ) . × – and HA at equilibrium. Also, determine the value of K a and p K a of the monobasic acid. pH = – log [H + ] Therefore, [H + ] = –pH = – .
× – p K a = – log( – ) = Alternatively, “Percent dissociation” is another useful method for measure of strength of a weak acid and is given as: Percent dissociation = [HA] dissociated /[HA] initial × % ( . ) Problem . Calculate the pH of .08M solution of hypochlorous acid, HOCl. The ionization constant of the acid is .
× – . Determine the percent dissociation of HOCl. HOCl(aq) + H O (l) H O + (aq) + ClO – (aq) Initial concentration (M) . Change to reach equilibrium concentration (M) – x + x +x equilibrium concentartion (M) .
– x x x K a = {[H O + ][ClO – ] / [HOCl]} = x / ( . –x) As x << . , therefore . – x .