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.
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.
Acids and Bases
When acids enter the water, the ions will separate. For instance, hydrogen chloride will separate into hydrogen and chlorine ions (HCL à H+ + CL-). Bases also undergo separation of their ions when enter the water. When sodium hydroxide enters the water it will separate into sodium and hydroxide ions (NaOH à Na+ + OH-).
When an acid substance ends up in water, it will give up a hydrogen ion to the water. The water will than become acid. The number of hydrogen ions that the water will receive determines the pH. When a basic substance enters the water it will take up hydrogen ions. This will lower the pH of the water. When a substance is strongly acidic it will give up more H+ ions to the water. Strong bases will give up more OH-.
Here we have summed up a list of products and their pH:
| pH | product |
| 14 | sodium hydroxide |
| 13 | lye |
| 12.4 | lyme |
| 11 | ammonia |
| 10.5 | manganese |
| 8.3 | backing powder |
| 7.4 | human blood |
| 7.0 | pure water |
| 6.6 | milk |
| 4.5 | tomatoes |
| 4.0 | win |
| 3.0 | apples |
| 2.0 | lemon juice |
| 0 | hydrochloric acid |
