pH and alkalinity
Water quality method: the pH
| Water quality and pH are often mentioned in the same sentence. The pH is a very important factor, because certain chemical processes can only take place when water has a certain pH. For instance, chlorine reactions only take place when the pH has a value of between 6,5 and 8. |
The pH is an indication for the acidity of a substance. It is determined by the number of free hydrogen ions (H+) in a substance.
Acidity is one of the most important properties of water. Water is a solvent for nearly all ions. The pH serves as an indicator that compares some of the most water-soluble ions.
The outcome of a pH-measurement is determined by a consideration between the number of H+ ions and the number of hydroxide (OH-) ions. When the number of H+ ions equals the number of OH- ions, the water is neutral. It will than have a pH of about 7.
The pH of water can vary between 0 and 14. When the pH of a substance is above 7, it is a basic substance. When the pH of a substance is below 7, it is an acid substance. The further the pH lies above or below 7, the more basic or acid a solution is.
The pH is a logarithmic factor; when a solution becomes ten times more acidic, the pH will fall by one unit. When a solution becomes a hundred times more acidic the pH will fall by two units.
The common term for pH is alkalinity.
|For more information about the effects of changing in pH on freshwater ecosystems, take a look at |
acids & alkalis in freshwater and for the correlation between pH en tempererature of pure water
For more information on water quality assessment, please check out our water quality assessment FAQ