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Indigo carmine

Indigo carmine
Other names 5,5'-indigodisulfonic acid sodium salt
CAS number 860-22-0
Molecular formula C16H8N2Na2O8S2
Molar mass 466.36
Appearance purple solid
Melting point

>300 °C

Solubility in water 10 g/L (25 °C)
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

Indigo Carmine, or 5,5'-indigodisulfonic acid sodium salt, is a pH indicator with the chemical formula C16H8N2Na2O8S2.



The primary use of Indigo carmine is as a pH indicator. It is blue at pH 11.4 and yellow at 13.0. . It is also used in the manufacturing of capusles as a soluble pigment.

Indigo Carmine (pH indicator)
below pH 11.4 above pH 13.0
11.4 13.0

Health concerns

Indigo carmine is harmful to the respiratory tract if swallowed. It is also an irritant to the skin and eyes. Proper laboratory cautions (Lab coat, gloves, goggles) are advised.

See also


This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Indigo_carmine". A list of authors is available in Wikipedia.
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