Eriochrome Black T (1787-61-7)

Eriochrome Black T Chemical Structure

What is Eriochrome Black T?

Eriochrome Black T (EBT) is a hydroxyl-aryl azo dye, typically supplied in the form of a monosodium salt. It is soluble in water and alcohol, but insoluble in common organic solvents. The color of Eriochrome Black T is pH-dependent, and it undergoes distinct color changes in different pH ranges.

Macsen Laboratories is the leading supplier of Eriochrome Black T with ISO certification.
Name of Product Eriochrome Black T
IUPAC Name sodium;3-hydroxy-4-[(1-hydroxynaphthalen-2-yl)diazenyl]-7-nitronaphthalene-1-sulfonate
Synonyms Mordant Black 11; Solochrome Black T; Fast Chrome Black T; Solochrome Black; Potting Black C; Chrome Black T
CAS No 1787-61-7
Molecular Formula C20H12N3NaO7S
Molecular Weight 461.4 g/mol
Pubchem CID 135465089


SR. No Criteria Limit/Specification
1 Appearance (Form) Solid Powder
2 Appearance (Color) Dark Red/Brownish-black solid with a faint metallic sheen
3 Odor Odorless
4 Solubility 0.1% (dist. water) Red Solution
5 Dye Content ~ 85%
6 Loss on drying (At 110°C,1hr) NMT 7%


  • Eriochrome Black T is commonly used as an indicator in complexometric titrations, especially those involving the determination of metal ions such as calcium (Ca2+), magnesium (Mg2+), and other transition metals.
  • As a complexometric indicator, it is frequently used in determining the hardness of water.
  • It is used as an indicator in various analytical procedures.
  • Additionally, Eriochrome Black T has been employed for the detection of rare earth metals.


Q. How to prepare Eriochrome black T indicator?

For preparing a 1% alcoholic solution of Eriochrome Black T to be used as a pH indicator, add 1 g of Eriochrome black T to 75 ml of ethyl alcohol. Swirl the mixture until fully dissolved. Dilute to a final volume of 100 ml with ethyl alcohol.

Q. Why Eriochrome Black T is used in EDTA titration?

Eriochrome black T (EBT) is used as an indicator in EDTA titrations. A distinct blue endpoint is attained upon the addition of an adequate amount of EDTA, which facilitates the chelation of metal ions that are bound to the EBT, thereby liberating the free EBT molecule.

Q. What is the color change of Eriochrome black?

Eriochrome Black T is blue in buffered solution at pH 10, but changes to red in the presence of calcium, magnesium, or other metal ions.

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