This document discusses autoionization of water and concepts related to acid-base chemistry including: - In neutral solutions, the concentrations of H3O+ and OH- are equal to each other based on the water ion product constant. - Solutions can be classified as neutral, acidic, or basic based on the relative concentrations of H3O+ and OH-. - Strong acids and bases completely ionize in solution, allowing their concentrations to determine H3O+ or OH- concentrations. - Weak acids and bases only partially ionize in solution, with their extent of dissociation determined by their acid or base ionization constant (Ka or Kb).

1. Auto Ionization of water
2H2O (l)  H3O+ + OH-
KW = [H3O+][OH-]
= 1.0 x 10-14 (ion product
constant for water at 250)
 NEUTRAL SOL’N: [H3O+] = [OH-]
 ACIDIC SOL’N: [H3O+] > [OH-]
 BASIC SOL’N: [H3O+] < [OH-]
 What is the concentrations of H3O+ &
OH- in neutral solutions?

2. Exercises
 Indicate whether the solution with the
following ion concentration is neutral, acidic,
or basic.
 [H+] = 4 x 10-9
 [OH-] = 1.01 x 10-7
 [OH-] = 7 x 10-13
 Given the following concentrations of OH-;
determine [H+].
 2 x 10-6
 0.010
 1.8 x 10-9

3. Ionization of Strong Acids and Bases
 Strong acids and bases completely
ionize in aqueous solution
HA + H2O  H3O+ + A-
B + H2O  OH- + BH+
 If [HNO3] = 0.05 M, [H+] = ?
 If [Mg(OH)2] = 0.25 M, [OH-] = ?
Consider the mole ratio of acid to H+ and base to
OH-

4. pH Box
Inter-converts pH to pOH to [OH-]
to [H+] and to pH again.

6. Examples
[H+] [OH-] pH pOH
0.012 M HCl 0.012 8.3 e -13 1.92 12.08
0.082 M NaOH 1.2 e-13 0.082 12.91 1.09
0.37 M
1.4e-14 0.74 13.87 0.13
Ba(OH)2

7. Exercise
 If a lemon juice has a concentration of
3.8 x 10-4 M, what is its pH?
 A feminine wash has a pH of 5.5, what is
the concentration of H3O+ present in this
soap?

8. Ionization of Weak Acids & Bases
 Weak acids and bases partially ionize
 The extent of dissociation depends on KA
and KB of each acid and base.
 KA = acid ionization constant
For the reaction:
HA + H2O  H3O+ + A-

9. Ionization of Weak Acids & Bases
 KB = base ionization constant
For the reaction:
XOH (aq)  OH- + X+
% Ionization = ( conc. Of H+ / conc of HA) x 100
= ( conc. Of OH-/ conc of XOH x 100)

10. pKA Box

11. Calculating KA from pH
 A student prepared a 0.10 M solution of
formic acid & measured its pH using a
pH meter. The pH at 250C was found to
be 2.38.
 Calculate KA for formic acid at this
temperature
 What is the % ionization of the solution?

12. Step by Step Solution
 Write the reaction, KA expression and
the equation
 Calculate [H+] from pH
 Tabulate (ICE)
 Substitute
Answer: KA = 1.8 x 10-4 % I = 4.2%

13. Using KA to calculate pH
 Calculate the pH of 0.3M solution of
acetic acid at 250C given KA = 1.8 x 10-5

14. Step by Step Solution
1. Write the reaction
2. Write the dissociation constant
expression and its value
3. Express the concentrations of the
unknown using the table (ICE)
4. Substitute the equilibrium conc’n into
the expression
Answer: pH = 2.64