<P> In chemistry , pH ( / piːˈ ( h ) eɪ tʃ / ) ( potential of hydrogen ) is a numeric scale used to specify the acidity or basicity of an aqueous solution . It is approximately the negative of the base 10 logarithm of the molar concentration , measured in units of moles per liter , of hydrogen ions . More precisely it is the negative of the base 10 logarithm 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 , at pH 7 ( 25 ° C ) , 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 . </P>
what is the definition of ph in water
potential of hydrogen