1. Acids and Bases pH Calculations
pH scale

2. pH Scale
Created to express acidity as a more simple number than molarity.
pH stands for “power” of the hydrogen ion concentration.
pH = - log [H+]
If [H+] = 1 x then pH = 7 (neutral)
[H+] = 1 x then pH = 3 (acid)
[H+] = 1 x then pH = 10 (base)
It is based on a logarithmic scale which has a base power of 10.
A pH of 1 differs from a pH of 2 by a factor of 10.

3. How to calculate pH….
What is the pH of a solution with a [H+] = 4.2 x 10-10M?
pH= -log [H+]
= -log (4.2 x 10-10)
= 9.38
Enter into calculator like this
or,
Enter 4.2 x in calculator and hit log button, then remove (-) sign.

4. To find the [H+] from pH [H+] = 10-pH
Determine the [H+] of a solution with a pH = 6.35.
[H+] = 10-pH
[H+] =
[H+] = 4.47 x 10-7 M
Find the “log” button on your calculator
Above this button it should say “10x”
You can use the 2nd key and this button to “un-log” the pH.
But, remember to put the (-) sign on the pH first!!

5. pOH We can also express the [OH-] as pOH pOH = -log [OH-]
pOH stands for the “power of the hydroxide ion.”
pOH<7 is basic
pOH=7 is neutral
pOH>7 acidic

6. pH and pOH together pH + pOH =14
What is the pH of a solution which has a pOH of 11.2 ? Is this solution acidic or basic?
pH = 14
pH = 2.8
So, the solution is acidic.

7. What is the pH of a solution with a [OH-] = 4.0 x 10–11M?
Step 1: Find pOH
pOH = -log[OH-]
= -log (4.0 x 10-11)
= 10.40
Step 2: Find pH using
pH + pOH = 14
pH = 14
pH = 3.60