1. Calculating Ion Concentration from pH

2. Calculating [Ion] from pH
We use logarithms to do this
N = 10x, then log N = x
[H+] = 10-pH
[H+] = invlog(-pH) [OH-] = invlog(-pOH)
On the calculator press 2nd log-pH#

3. Calculations of [H+] or [OH-]
Ex 1: What are [H+] and [OH-] in a healthy person’s blood that has a pH = 7.40 at temp 298 K?
Kw = [H+] x [OH-]
1 x = [3.98 x 10-8] x [OH-]
3.98 x x 10-8
2.51 x = [OH-]
[H+] = invlog(-pH)
[H+] = invlog(-7.40)
[H+] = 3.98 x 10-8

4. Calculations of [H+] or [OH-]
Ex 2: What are [H+] and [OH-] at a pH = 2.3?
Kw = [H+] x [OH-]
1 x = [0.0050] x [OH-]
2.0 x = [OH-]
[H+] = invlog(-pH)
[H+] = invlog(-2.3)
[H+] =

5. Calculations of [H+] or [OH-]
Ex 3: What are [H+] and [OH-] at a pH = 5.54?
Kw = [H+] x [OH-]
1 x = [2.88 x 10-6] x [OH-]
2.88 x x 10-6
3.47 x = [OH-]
[H+] = invlog(-pH)
[H+] = invlog(-5.54)
[H+] = 2.88 x 10-6