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Scale from 0 to 14 for measuring acidity or alkalinity. A pH of 7.0 indicates neutrality, below 7 is acid, while above 7 is alkaline. Strong acids, such as those used in automobile batteries, have a pH of about 2; strong alkalis such as sodium hydroxide are pH 13.
Acidic fruits such as citrus fruits are about pH 4. Fertile soils have a pH of about 6.5 to 7.0, while weak alkalis such as soap are 9 to 10.
The pH value of a solution equals the negative logarithm of the concentration of hydrogen ions.
P(otential of) H(ydrogen); the logarithm of the reciprocal of hydrogen-ion concentration in gram atoms per liter; used as a measure of the acidity or alkalinity of a solution on a scale of 0-14 (where 7 is neutral); SYN. pH scale.