Eriochrome Black T

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]

Eriochrome Black T
Names
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; Erio T
Identifiers
3D model (JSmol)
Abbreviations EBT
4121162
ECHA InfoCard 100.015.683
EC Number
  • 217-250-3
MeSH Eriochrome+black+T
RTECS number
  • QK2197000
UNII
UN number 2923
  • InChI=1S/C20H13N3O7S.Na/c24-17-10-18(31(28,29)30)15-9-12(23(26)27)6-7-14(15)19(17)22-21-16-8-5-11-3-1-2-4-13(11)20(16)25;/h1-10,24-25H,(H,28,29,30);/q;+1/p-1/b22-21+; Y
    Key: AMMWFYKTZVIRFN-QUABFQRHSA-M Y
  • C1=CC=C2C(=C1)C=CC(=C2O)/N=N/C3=C4C=CC(=CC4=C(C=C3O)S(=O)(=O)[O-])[N+](=O)[O-].[Na+]
Properties
C20H12N3O7SNa
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).
N verify (what is YN ?)
Infobox references

In its deprotonated 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.

Applications

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]

References
  1. "Eriochrome Black T ACS reagent indicator grade 1787-61-7".
  2. Dubenskaya, L. O.; Levitskaya, G. D. (1999). "Use of eriochrome black T for the polarographic determination of rare-earth metals". Journal of Analytical Chemistry. 54 (7): 655–657. ISSN 1061-9348.
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