Indicator

Name:
Indicator
Detailed information:
An organic substance (usually a dye or intermediate) that indicates by a change in its color the presence, absence, or concentration of some other substance, or the degree of reaction between two or more other substances. The most common example is the use of acid-base indicators such as litmus, phenolphthalein, and methyl orange to indicate the presence or absence of acids and bases, or the approximate concentration of hydrogen ion in a solution.

Use:

Analytical chemistry.The pH ranges of several typical indicators are as follows: alizarin yellow R 10.1–12.0 yellow to red methyl orange 3.1– 4.4 red to yellow phenolphthalein 8.3–10.0 colorless to red phenol red 6.8– 8.4 yellow to red litmus 4.4– 8.3 red to blue Congo red 3.0– 5.2 blue to red bromthymol blue 6.0– 7.6 yellow to blue chlorphenol red 5.2– 6.8 yellow to red cresol purple 7.4– 9.0 yellow to purple

See Titration; pH.