Page 72 - [B._MURPHY,_C._MURPHY,_B._HATHAWAY]_A_working_meth

56 Chapter 5
(a) If the highest concentration that remains is that of an acid
or base, acid or base dissociation occurs:

Acid dissociation: HA + H20 * H30+ + A-,
Ka = {[H30+I[A-I)/[HAI;
Base dissociation: B + H20 + BH+ + OH-,
1
Kb = { [BH ' [OH-] ) /[B1.
(b) If the highest concentration that remains is that of an
anion or cation, anion or cation hydrolysis occurs:

Anion hydrolysis: A- + H20 * HA + OH-,
Kh = ([HA][OH-])/[A-]
Cation hydrolysis: CH+ + H20 * C + H30+,
Kh = ([CI[H30'1)/[cH']

9. Calculate the concentration of all reactants and products in
solution, letting x = [H30+].
10. Use the equilibrium expression to calculate the value of x:
VAA + WB * VCC + mD, Kc = { [C]" [D]-}/{ [A]'* [BIVB}, i.e.
of the form, productslreactants:
(a) K, = K, for acid dissociation; (b) K, = Kb for base
dissociation; (c) K, = Kh for anion or cation hydrolysis, where:

and K, =
11. Calculate the pH of the solution: pH =-loglo[H30+], where
pH + pOH = 14.

Worked Examples

Example No. 1: In a titration of 35 crn3 0.1 M CH3C02H with 0.1
M NaOH, determine the pH of the solution after the addition of 15
cm3 of base, given that Ka(CH3C02H) = 1.8 x

Solution:
1. Acid/base reaction.
2. NaOH-strong base; CH3C02H-weak acid.