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 AcidToward AlkaliRange of pH
Methyl yellowRedYellow2.9-4.0
Congo redBlueRed3.0-5.2
Methyl orangeRedYellow3.1-4.4
Methyl redRedYellow4.2-6.2
LitmusRedBlue4.5-8.3
Bromcresol purpleYellowPurple5.2-6.8
Bromothymol blueYellowBlue6.0-7.6
Phenol redYellowRed6.8-8.4
PhenolphthaleinColorlessPink8.2-10.0

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