An Acid is a chemical agent that releases hydrogen ions when added to water. The term pH, which in general is the measure of the number of acidity or alkalinity that is in a solution. More specifically, it is a measure of the amount of protons or hydrogen ions that are present in an aqueous solution. An acid has a pH of less than 7. (Opposite of the Alkali or Alkaline)

Related Definitions in the Project: The Property and Unit