The Math of PH

PH is defined as the NEGATIVE log of the hydrogen ion concentration

PH = -log [H +]

Because H + is always in equilibrium with water and INVERSLY proportional to OH - concentration (as one increases the other decreases).

HOH <---> H + + OH -

We can also have the "POWER of the hydroxide ion" value, or pOH:

POH = -log [ OH -]

Also remember the ion product constant for water:

[H +] x [ OH -] = 1x10 -14 moles/liter 2

With some mathematical manipulation this also means that:

PH + pOH = 14

With all this information, you can solve problems involving pH:

PROBLEMS

1. What is the pH of a solution with a [H +] of 1 x 10 -8?

2. What is the [H +] of a solution with a pH of 3?

3. What is the pOH of a solution with a pH of 5?

4. What is the [ OH -] of a solution with a pH of 4?

5. If you wanted to change the pH of a solution from 3 to 5, how many times would you dilute it?