Base | Definition, Examples, & Facts | Britannica

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External Websites

• Royal Society of Chemistry - The theory of acids and bases
• OpenStax - Chemistry 2e - Relative Strengths of Acids and Bases
• Chemistry LibreTexts - Acids- Properties and Examples
• Chemistry LibreTexts - Bases: Properties and Examples
• Open Library Publishing Platform - Enhanced Introductory College Chemistry - Acids and Bases
• National Center for Biotechnology Information - PubMed Central - Acid-Base Basics
• UEN Digital Press with Pressbooks - Strength of Bases

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base, in chemistry, any substance that in water solution is slippery to the touch, tastes bitter, changes the colour of indicators (e.g., turns red litmus paper blue), reacts with acids to form salts, and promotes certain chemical reactions (base catalysis). Examples of bases are the hydroxides of the alkali and alkaline earth metals (sodium, calcium, etc.) and the water solutions of ammonia or its organic derivatives (amines). Such substances produce hydroxide ions (OH-) in water solutions (see Arrhenius theory).

Related Topics: alkaloid alkali hydroxide Lewis base proton acceptor (Show more) On the Web: Chemistry LibreTexts - Acids- Properties and Examples (Mar. 06, 2026) (Show more) See all related content

Broader definitions of a base, to include substances that exhibit typical basic behaviour as pure compounds or when dissolved in solvents other than water, are given by the Brønsted-Lowry theory and the Lewis theory.

The Editors of Encyclopaedia BritannicaThis article was most recently revised and updated by Barbara A. Schreiber.