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Examples of the pH of some substances by OpenStax College.
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pH is a measure for the acidity or basicity of a substance dissolved in water.


The idea of pH was first introduced by the Danish chemist Søren Peder Lauritz Sørensen at the Carlsberg Laboratory in 1909. It was later revised to the modern concept of pH in 1924 to accommodate definitions and measurements in terms of electrochemical cells.

How it works[edit]

The scale assigns a number from 0-14[note 1] to a water solution, depending on its acidity/basicity. Acidity/basicity is based on the concentration of hydrogen ions. 0 is the most acidic and 14 is the most basic. Pure water is considered neutral, with a pH of 7. Water exposed to air becomes mildly acidic, due to absorbing CO2 from the atmosphere. The pH scale is a logarithmic scale. Therefore, an increase in pH from 4.0 to 5.0 is equal to a ten-fold increase in the concentration of hydrogen ions.


0-1—HCl, battery acid

2-3—soda, lemon juice, vinegar

4-5—lysosomes, black coffee

6-7—milk, saliva, pure water

8-9—sea water, baking soda

10-11—ammonia, lye


14—liquid drain cleaner


See also: pH woo

PH woo has to do with claiming that changing the pH balance of your body will miraculously cause your health to improve. It is totally correct. [citation NOT needed]

Works cited[edit]


  1. The pH of a solution can be negative or greater than 15.