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 p H 1 to 5 and yellow from p H 5 to 9 methyl orange, yellow in basic and neutral solutions and reddish below p H 3.7 phenolphthalein, colorless in acid and neutral solutions, pink at about p H 8.5, and purplish at p H 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.

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