pH, a scale representing the relative acidity (or alkalinity) of a solution, in which a value of 7.0 is neutral, below 7.0 is acid, and above 7.0 is alkaline. The numeric pH value indicates the relative concentration of hydrogen ions in the solution compared with that of a standard (1 molar) solution. It is equal to the negative log of the hydrogen ion concentration expressed in moles per liter. Abbreviation for potential hydrogen. See also acid, acid-base balance.
