pH

The pH of a solution containing hydrogen ions is given by the equation:

pH = - log [ a(H⁺_aq) ]

where a(H⁺_aq) is the activity of the H⁺_{aq ions.}

When the solution is sufficiently dilute, the term a(H⁺_aq) is comparable with the value of the concentration of hydrogen ions expressed in mol/L, i.e. [H⁺_aq].

The pH of pure water, a neutral solvent, is equal to 7 at 25°C.

Acid solutions have a pH lower than 7 while basic solution have a pH greater than 7

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