PH

A measure of the concentration of protons (H⁺) in a solution and, therefore, its acidity or alkalinity.

The formula for calculating pH is:

-LOG₁₀[H⁺]

([H⁺] means the concentration of H⁺ ions, and is measures in moles? per litre)

A pH of 7 indicates neutrality, e.g. pure water. A lower pH number indicates increasing strength of acidity, and a higher pH number indicates increasing strength of alkilinity.