PH

A numerical designation given to the acidity and alkalinity of an aqueous solution, on a scale of 1 to 14. Technically, pH is common logarithm of the reciprocal of the hydrogen-ion concentration of a solution. A pH value of 7 (pure water at 25º C) indicates neutrality, while values below 7 (7 to 1) indicate acidity and above 7 (7 to 14) indicate alkalinity.