pH Definition

Converts hydrogen-ion concentration into a compact logarithmic scale so acidity can be reported as a single number between 0 and 14.

$$\mathrm{pH}=-{\log }_{10}[{\mathrm{H}}^{+}]$$

Variables

Symbol	Meaning	Unit
$[{\mathrm{H}}^{+}]$	Hydrogen-ion (proton) concentration	mol/L

Worked example

Pure water at 25 C has [H+] = 10^-7 mol/L, so pH = -log10(10^-7) = 7.

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Part of The Blueprint of Water