In
chemistry,
pH is a numeric scale used to specify the
acidity or basicity(alkalinity) of an
aqueous solution. It is roughly the negative of the
logarithm to base 10 of the concentration, measured in units of
moles per liter, of hydrogen ions or H+. More precisely it is the negative of the logarithm to base 10 of the
activity of the
hydrogen ion. Solutions with a pH less than 7 are acidic and solutions with a pH greater than 7 are
basic.
Pure water is neutral, being neither an acid nor a base. Contrary to popular belief, the pH value can be less than 0 or greater than 14 for very strong acids and bases respectively.