The pH scale was developed to provide an easy way to describe how acidic or basic (alkaline) a solution is. Acids have a low pH, while bases have a high pH; pure water is neutral—neither acidic nor basic.
In 1909, the pH scale was proposed by the Danish scientist P. L. Sörenson. Up until then, describing the acidity of a solution was tedious and difficult.
Acids and Bases
An acid produces hydronium ions (H+) when dissolved in water, while a base produces hydroxide (OH-) ions when dissolved in water.
The pH Scale
The pH scale ranges from 1 to 14. Acids have a pH less than 7, while bases have a pH greater than 7.
Any time the pH of a solution is moved closer to 7, it is being neutralized. To raise pH, add a base; to lower pH, add an acid.
Litmus paper is used to obtain a crude measure of pH. Filter paper is treated with a dye that changes color, depending on pH; blue litmus paper turns red in an acid, and red litmus paper turns blue in a base.
For accurate pH measurements, a pH meter is better than pH test paper.