Eriochrome Black T

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Eriochrome Black T
Wireframe model of an eriochrome black T minor tautomer
Sample of Eriochrome Black T
Abbreviations EBT
CAS number 1787-61-7 N
PubChem 6808871 YesY, 5359641 (4EYesY, 5351620 (4ZYesY
ChemSpider 10483790 YesY, 4508620 (4ZYesY
EC number 217-250-3
UN number 2923
MeSH Eriochrome+black+T
RTECS number QK2197000
Beilstein Reference 4121162
Jmol-3D images Image 1
Image 2
Molecular formula C20H12N3O7SNa
Molar mass 461.381 g/mol
Appearance dark red/brown powder
Acidity (pKa) 6.2, 11.55
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

Eriochrome Black T is a complexometric indicator that is part of the complexometric titrations, e.g. in the water hardness determination process. It is an azo dye. Eriochrome is a trademark of Ciba-Geigy.[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 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]