pH
pH is a measure of how acidic or basic (alkaline) a solution is. It is a scale that ranges from 0 to 14:
- pH less than 7: The solution is acidic. The lower the pH, the more acidic the solution is.
- pH of 7: The solution is neutral, meaning it is neither acidic nor basic. Pure water is an example of a neutral solution.
- pH greater than 7: The solution is basic (alkaline). The higher the pH, the more basic the solution is.
The pH scale is logarithmic, meaning each whole number change on the scale represents a tenfold change in the concentration of hydrogen ions.
For example, a solution with a pH of 4 is ten times more acidic than a solution with a pH of 5.
In chemical terms, pH is defined as the negative logarithm (base 10) of the hydrogen ion concentration [H+] in a solution:
pH = −log[𝐻+]
This means that as the concentration of hydrogen ions increases, the pH value decreases, indicating higher acidity.
Some Common Examples
pH | H+ Concentration | Example |
---|---|---|
0 | 10 000 000 | battery acid |
5 | 100 | black coffee |
7 | 1 | pure water |
9 | 0.01 | baking soda |
13 | 0.000 001 | bleach |
14 | 0.000 000 1 | liquid drain cleaner |