1. pH and pOH
Acid
Neutral
Base

2. pH [H+] = 10-pH . . . . Hence “power of hydrogen.” pH = -log [H+]
Low pH = acid
pH = “power of hydrogen”
Power is the math power, as in 10 to the second power = 102
[H+] = concentration of H+ ion (molarity)
The higher the concentration, the stronger the acid, the lower the pH
[H+] = 10-pH Hence “power of hydrogen.”
Solving for pH:
pH = -log [H+]

3. pH examples
What is the pH of a solution if the H+ concentration is 3.4 X 10-3 M?
pH = -log [H+]
pH = -log (3.4 X 10-3 M)
pH = 2.5
What is the H+ concentration of an acid with a pH of 3.0?
[H+] = 10-pH
[H+] =
[H+] = M or 1.0 X 10-3 M

4. pOH [OH-] = 10-pOH pOH = -log [OH-] Low pOH = base
pOH = a measure of hydroxide ion concentration
pOH is derived from pH
[OH-] = concentration of OH- ion (molarity)
The higher the concentration, the stronger the base, the lower the pOH
[OH-] = 10-pOH
Solving for pOH:
pOH = -log [OH-]

5. pOH Examples
What is the pOH of a solution if the OH- concentration is 3.4 X 10-6 M?
pOH = -log [OH-]
pOH = -log (3.4 X 10-6 M)
pOH = 5.5
What is the OH- concentration of a base with a pOH of 2.0?
[OH-] = 10-pOH
[OH-] = 10-2
[OH-] = .010 M or 1.0 X 10-2 M

6. pH and pOH pH is a measurement of the [H+] pH = -log [H+]
pOH is a measurement of the [OH-]
pOH = -log [OH-]
pH and pOH must equal 14
pH + pOH = 14
pOH can be found when you know pH and vise versa
In pure water, pH and pOH are both 7.
All aqueous solutions have a pH and a pOH.

7. Example
If [H+] = 1.0 x 10-7 M, then what is the pH? pH = -log [H+] pH = -log (1.0 x 10-7) pH = 7.0 You must use the log key.

8. Example
If the [OH-] is 5.01 x 10-4 M, what is the pOH? pOH = -log [OH-] pOH = -log (5.01 x 10-4) pOH = 3.30

9. Sample Problem
In household bleach, the concentration of OH- ions is 5.00 x 10-2 M. What is the pH?
pOH = -log [OH-]
pOH = -log (5.00 x 10-2)
pOH = 1.30
pOH + pH = 14
pH =
pH = 12.7