pH Definition
An introduction to pH
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pH can be viewed as an abbreviation for power of hydrogen or more completely, power of the concentration of the hydrogen ion.
The mathematical definition of pH is a bit less intuitive but in general more useful. It says that the pH is equal to to the negative logarithmic value of the Hydrogen ion (H+) concentration, or
pH = -log [H+]
pH is alternatively defined mathematically as the negative logarithmic value of the Hydroxonium ion (H3O+) concentration. Using the Bronsted-Lowry approach that would be
pH = -log [H3O+]
pH values are calculated in powers of 10. The hydrogen ion concentration of a solution with pH 1.0 is 10 times larger than in a solution with pH 2.0. The larger the hydrogen ion concentration, the smaller the pH.
- When the pH is above 7, the solution is basic (alkaline), and when it is below 7, the solution is acidic.
In pure neutral water the concentration of hydrogen and hydroxide ions are both 10-7 equivalent per liter.
| pH | Ion Concentration (gram equivalent per liter) | Type of Solution |
| 0 | 1,0 | Acid Solution - hydrogen ions - H+ |
| 1 | 0,1 | |
| 2 | 0,01 | |
| 3 | 0,001 | |
| 4 | 0,0001 | |
| 5 | 0,00001 | |
| 6 | 0,000001 | |
| 7 | 0,0000001 | Neutral Solution |
| 8 | 0,000001 | Basic (alkaline) Solution - Hydroxide ions OH- |
| 9 | 0,00001 | |
| 10 | 0,0001 | |
| 11 | 0,001 | |
| 12 | 0,01 | |
| 13 | 0,1 | |
| 14 | 1,0 |
Common pH Values
pH values in some common products:
| Product | pH |
| Battery Acid | 0 |
| HCl in stomach acid | 1 |
| Lemon juice, vinegar | 2-3 |
| Orange juice | 3-4 |
| Acid rain | 4 |
| Black coffee | 5 |
| Urine, salvia | 6 |
| Pure water | 7 |
| Sea water | 8 |
| Baking soda | 9 |
| Ammonia solution | 10-11 |
| Soapy water | 12 |
| Bleach | 13 |
| Oven cleaner | 13-14 |
| Drain cleaner | 14 |
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