pH
potential hydrogen (pH).
Used to express the degree of acidity and alkalinity in an aqueous solution, usually on a scale of 1-14, where H+ is the hydrogen-ion concentration. Technically, pH is defined as the negative logarithm of the effective hydrogen-ion concentration in gram equivalents per liter of solution: pH equals log10 (1/H+). A pH value of 7 (pure water at 77°F, 25°C) indicates neutrality, lower numbers indicate acidity, and higher numbers indicate alkalinity. The pH can be measured by specially prepared pH test papers. Syn: pH value.