Eriochrome black T

Structural formula
General
Surname	Eriochrome black T
other names	Sodium 3-hydroxy-4 - [(1-hydroxy-2-naphthyl) diazenyl] -7-nitro-1-naphthalenesulfonate ( IUPAC ); CI Mordant Black 11; CI 14645; Erio T; Chromogenic black; Chrome black;
Molecular formula	C 20 H 12 N 3 NaO 7 S
Brief description	black solid
External identifiers / databases
EC number	217-250-3
ECHA InfoCard	100.015.683
PubChem	135465089
ChemSpider	21159539
Wikidata	Q414854
properties
Molar mass	461.38 g mol −1
Physical state	firmly
solubility	soluble in water (50 g l −1 at 20 ° C)
safety instructions
H and P phrases	H: 319-411
	P: 273-305 + 351 + 338
Toxicological data	17,590 mg kg −1 ( LD 50 , rat , oral )
	As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Eriochrome black T is an azo dye that is used as an indicator in complexometry and for determining water hardness . The intense color is due to the azo group and the water solubility due to the sulfonic acid group .

properties

Aqueous solutions of eriochrome black are wine red up to a pH value of 6.3. The sulfonic acid is deprotonated here and the two hydroxyl groups are protonated. By adding bases , the two hydroxyl groups are gradually deprotonated and the solution initially turns deep blue (dianion). If the pH value increases further, the color changes to orange at pH 11.5 (trianion). These indicator anions now form a weak purple-colored complex with bivalent metal ions , which is destroyed again by adding a stronger complexing agent such as EDTA . In order to create a greater contrast at the transition point, eriochrome black T is often used as a mixed indicator with methyl orange . This changes the color from red via a gray intermediate tone to green.

Structure of Eriochrome Black T at different pH values and the corresponding metal complex

Individual evidence

↑ ^a ^b Data sheet Eriochromschwarz T (CI 14645) (PDF) from Merck , accessed on March 30, 2011.
↑ ^a ^b Entry on Eriochrome black T in the GESTIS substance database of the IFA , accessed on February 10, 2017(JavaScript required) .
↑ Entry on Eriochrome Black T in the ChemIDplus database of the United States National Library of Medicine (NLM) .
↑ Hans Peter Latscha, Helmut Alfons Klein: Analytical Chemistry . Chemistry - basic knowledge III. 3. Edition. Springer-Verlag, Berlin, Heidelberg 1995, ISBN 978-3-540-58456-8 , pp. 288 ( limited preview in Google Book search).
↑ ^a ^b G.-O. Müller: Quantitative-inorganic internship , 7th edition, Verlag Harri Deutsch, Frankfurt / Main 1992, ISBN 3-8171-1211-4 , pp. 124-125.
↑ Lutz H. Gade: coordination chemistry . 1st edition, 3rd corrected reprint. Wiley VHC, Weinheim 1998, ISBN 978-3-527-29503-6 , pp. 241 ( limited preview in Google Book search).

[Merck-1] Data sheet Eriochromschwarz T (CI 14645) (PDF) from Merck , accessed on March 30, 2011.

[GESTIS-2] Entry on Eriochrome black T in the GESTIS substance database of the IFA , accessed on February 10, 2017(JavaScript required) .

[ChemIDplus-3] Entry on Eriochrome Black T in the ChemIDplus database of the United States National Library of Medicine (NLM) .

[Latscha-4] Hans Peter Latscha, Helmut Alfons Klein: Analytical Chemistry . Chemistry - basic knowledge III. 3. Edition. Springer-Verlag, Berlin, Heidelberg 1995, ISBN 978-3-540-58456-8 , pp. 288 ( limited preview in Google Book search).

[go-5] G.-O. Müller: Quantitative-inorganic internship , 7th edition, Verlag Harri Deutsch, Frankfurt / Main 1992, ISBN 3-8171-1211-4 , pp. 124-125.

[6] Lutz H. Gade: coordination chemistry . 1st edition, 3rd corrected reprint. Wiley VHC, Weinheim 1998, ISBN 978-3-527-29503-6 , pp. 241 ( limited preview in Google Book search).