1. Calculations of pH
Definition: pH is abbreviation for
french pouvoir hydrogene. It is
expressed as the negative log of the
concentration of hydronium ion
pH = -log [H3O+]
pH < 7 = acid

2. pOH
pOH is the concentration of hydroxide
ion
pOH = -log [OH-]
pH > 7 is a base
pOH < 7 is a base
pH + pOH of a solution = 14
 If you know pH, you can
calculation pOH and vice versa

3. Calculating pH from [H3O+]
pH of an acid with 1 x 10–6 M [H3O+] is 6
 pOH is 8 (6 + 8 = 14)
pH of an acid with 1x 10-5 M [H3O+] is 5
 pOH is 9 (5 + 9 = 14)
Practice: What is the pH of the following?
 1 x 10-3 M HCl
 1 x 10-5 M HNO3
 1 x 10-4 M NaOH
 1 x 10–2 M KOH

4. Using a Calculator
[H3O+] = 3.4 x 10-5 M, find pH
pH = -log [3.4 x 10-5]
pH = 4.5
Steps: 3.4 EE 5 +/-log +/-
Practice: find pH
 [H3O+] = 6.7 x 10-4
 [H3O+] = 2.5 x 10-2
 [H3O+] = 2.5 x 10-6

5. Calculating [H3O+] from pH
If pH = 7.52, find [H3O+] and [OH-]
 pH = -log [H3O+]
 [H3O+] = antilog(-pH)
 [H3O+] = antilog(-7.52)
 Steps 7.52 +/- 2nd 10x
 [H3O+] = 3.02 x 10-8
 [H3O+] [OH-] = 1 x 10-14
 [OH-] = 3.3 x 10-7
 Practice, find [H3O+] and [OH-] from pH
 pH = 5.0
 pH = 12.0
 pH = 1.5