Eriochrome Black T

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Eriochrome Black T
Wireframe model of an eriochrome black T minor tautomer
Sample of Eriochrome Black T
Preferred IUPAC name
Sodium 1-[1-Hydroxynaphthylazo]-6-nitro-2-naphthol-4-sulfonate
Systematic IUPAC name
Sodium 4-[2-(1-hydroxynaphthalen-2-yl)hydrazin-1-ylidene]-7-nitro-3-oxo-3,4-dihydronaphthalene-1-sulfonate
Other names
Sodium 4-[2-(1-hydroxynaphthalen-2-yl)hydrazin-1-ylidene]-7-nitro-3-oxonaphthalene-1-sulfonate; Solochrome Black T; ET-00
3D model (Jmol)
Abbreviations EBT
ECHA InfoCard 100.015.683
EC Number 217-250-3
MeSH Eriochrome+black+T
RTECS number QK2197000
UN number 2923
Molar mass 461.381 g/mol
Appearance dark red/brown powder
Acidity (pKa) 6.2, 11.55
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Eriochrome Black T is a complexometric indicator that is used in complexometric titrations, e.g. in the water hardness determination process. It is an azo dye. Eriochrome is a trademark of Huntsman Petrochemical, LLC.[1]

In its protonated form, Eriochrome Black T is blue. It turns red when it forms a complex with calcium, magnesium, or other metal ions.

EBT is blue in a buffered solution at pH 10. It turns red when Ca2+ ions are added.


When used as an indicator in an EDTA titration, the characteristic blue end-point is reached when sufficient EDTA is added and the metal ions bound to the indicator are chelated by EDTA, leaving the free indicator molecule.

Eriochrome Black T has also been used to detect the presence of rare earth metals.[2]


External links[edit]