In chemistry, there are three definitions in common use of the word "base": Arrhenius bases, Brønsted bases, and Lewis bases. All definitions agree that bases are substances that react with acids, as originally proposed by G.-F. Rouelle in the mid-18th century.
Soaps are weak bases formed by the reaction of fatty acids with sodium hydroxide or potassium hydroxide.
Ammonia fumes from aqueous ammonium hydroxide (in test tube) reacting with hydrochloric acid (in beaker) to produce ammonium chloride (white smoke).
Sodium hydroxide
Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and compounds made of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo during reactions with other substances. Chemistry also addresses the nature of chemical bonds in chemical compounds.
Image: Sulfur sample
Image: Sal (close)
Laboratory, Institute of Biochemistry, University of Cologne in Germany
Solutions of substances in reagent bottles, including ammonium hydroxide and nitric acid, illuminated in different colors