Color reaction

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In chemistry, a color reaction or colour reaction is a chemical reaction that is used to transform colorless chemical compounds into colored derivatives which can be detected visually or with the aid of a colorimeter.

The concentration of a colorless solution cannot normally be determined with a colorimeter. The addition of a color reagent leads to a color reaction and the absorbance of the colored product can then be measured with a colorimeter.

A change in absorbance in the ultraviolet range cannot be detected by eye but can be measured by a suitably equipped colorimeter. A special colorimeter is required because standard colorimeters cannot operate below a wavelength of 400 nanometers. It is also necessary to use fused quartz cuvettes because glass is opaque to ultraviolet.

Color reagents[edit]

Many different color reagents have been developed for determining the concentrations of different substances. For example, Nessler's reagent can be used to determine the concentration of a solution of ammonia.

Thin layer chromatography[edit]

In thin layer chromatography (TLC) color reactions are frequently used to detect compound spots by dipping the plate into the reagent or by spraying the reagent onto the plates.

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