1. pH

2. Definitions and Formulas
The pH scale is defined as the negative log of the concentration of H+:
pH = -log[H+]
The pOH scale is defined as the negative log of the concentration of OH-, [OH-].
pOH = -log[OH-]
With this scale, calculating the pOH can be done in the same manner as the pH scale.
pH + pOH = 14

3. Examples
What is the pH of a solution that contains 25 g of hydrochloric acid (HCl) dissolved in 1.5 L of water?

4. Quiz Determine the pH of a .0034 M HNO3 solution.
Determine the pOH of the solution in #1.
What is the pH of a 2.4 x 10-5 M HCl solution?

5. Auto-Ionization of Water
In water, Kc= [H+][OH-]
55.5 M
[OH-]= Kw [H30+]= Kw
[H30+] [OH-]
ion product constant for water  Kc (55.5M) = [H+][OH-] = Kw
 Kw= [H30+] [OH-]
 Kw=
Example: What is the hydroxide ion concentration in an aqueous solution that is 4.0 x 10-5 M H30+?
[OH-] = (1.0 x 10-14)
(4.0 x 10-5)
=2.5 x M

6. Practice
What is the hydronium ion concentration in an aqueous solution containing 3.5 x 10-7 OH-?
[H30+] = (1.0 x 10-14)
(3.5 x 10-7)
=2.9 x 10-8
What is the hydroxide ion concentration in an aqueous solution containing 8.34 x H30+ ?
[OH-] = (1.0 x 10-14)
(8.34 x 10-12)
=1.20 x 10 -3

7. Strong Acids dissociate completely in water to form hydronium ion(s)
Examples
HCl
HNO3
H2SO4

8. Strong Bases dissociate completely in water to form hydroxide ions
Examples:
NaOH
KOH
Ca(OH)2