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A strip of indicator paper, turned blue, rests on a circular pH color chart, showing the liquid tested is alkaline.
Understanding acids, bases, and the pH scale
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A strip of indicator paper, turned blue, rests on a circular pH color chart, showing the liquid tested is alkaline.
Alkaline testing Indicator paper is used to determine the pH of a liquid. The paper will turn blue when a solution is alkaline.

base

chemical compound
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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).

Understanding acids, bases, and the pH scale
Understanding acids, bases, and the pH scaleThe fundamentals of acids and bases and how the pH scale is used to measure them.
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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.