indicators, acid-base

indicators, acid-base, organic compounds that, in aqueous solution, exhibit color changes indicative of the acidity or basicity of the solution. Common indicators include p-nitrophenol, which is colorless from pH 1 to 5 and yellow from pH 5 to 9; methyl orange, yellow in basic and neutral solutions and reddish below pH 3.7; phenolphthalein, colorless in acid and neutral solutions, pink at about pH 8.5, and purplish at pH 10; and litmus. Most indicators are also used in large amounts for dyeing; small quantities are nonetheless invaluable for use as indicators in chemical laboratories.

The Columbia Electronic Encyclopedia, 6th ed. Copyright 2012, Columbia University Press. All rights reserved.

See more Encyclopedia articles on: Organic Chemistry