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What Is a pH Level?

By Philip McIntosh ; Updated September 21, 2017

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

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.

pH Meters

For accurate pH measurements, a pH meter is better than pH test paper.


About the Author


Philip McIntosh has more than 30 years of experience as an equipment engineer, scientific investigator and educator. He has been writing for 16 years, and his work has appeared in scientific journals, popular science magazines, trade journals and on science and technology websites. McIntosh holds a B.S. in botany and chemistry, and an M.A. in biological science.