indicator

(in″dĭ-kāt′ŏr )

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[L. indicare, to show]
In chemical analysis, a substance that can be used to determine pH. In a more general sense, any substance that can be used to determine the completeness of a chemical reaction, as in volumetric analysis. SEE TABLE: Colors of Indicators of pH
Colors of Indicators of pH

	Color
	Toward Acid	Toward Alkali	Range of pH
Methyl yellow	Red	Yellow	2.9-4.0
Congo red	Blue	Red	3.0-5.2
Methyl orange	Red	Yellow	3.1-4.4
Methyl red	Red	Yellow	4.2-6.2
Litmus	Red	Blue	4.5-8.3
Bromcresol purple	Yellow	Purple	5.2-6.8
Bromothymol blue	Yellow	Blue	6.0-7.6
Phenol red	Yellow	Red	6.8-8.4
Phenolphthalein	Colorless	Pink	8.2-10.0

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