The pH and pOH scales
From Chemistry Resource
pH and pOH are quantitative ways to express solutions of acids and bases. The pH scale is a more convenient way than using exponential notation for expressing concentration of hydrogen ions.
pH scale
In general, for any hydrogen ion concentration of
- 1 x 10-n moles/liter = [H+]
the pH is equal to
- pH = n
Mathematically, pH is defined as:
- pH = - log [H+]
Enter into your calculator the following H+ ion concentrations and see if you arrive at the pH values as indicated.
| [H+] (molarity) | pH |
| 1 x 10-1 | 1 |
| 1 x 10-3 | 3 |
| 1 x 10-9 | 9 |
| 1 x 10-11 | 11 |
pH of common solutions
| Solution | pH |
| lemon juice | 2.3 |
| vinegar | 2.5-3.5 |
| coke | 2.0-4.0 |
| blood | 7.4 |
| milk of magnesia | 10.5 |
| household ammonia | 11 |
pOH scale
In general, for any hydroxide ion concentration of
- 1 x 10-n moles/liter = [OH-]
the pOH is equal to
pOH = n
When the solution's pH is added to its pOH, the result is always equal to 14.
- pH + pOH = 14
