Eriochrome Black T

• Erio T
• Chromogenschwarz
• Chrome Black
• Mordant Black 11
• 2-hydroxy- 1 -(1- hydroxynaphthyl -2 -azo ) -6 - nitronaphthalene - 4-sulfonic acid sodium salt

Black solid

Fixed

0.9 g · cm -3

Decomposition

50 g · l-1 in water at 20 ° C

Attention

17,590 mg · kg -1 ( LD50, rat, oral)

Template: Infobox chemical / molecular formula search available

Eriochrome black T is an azo dye, which is used as an indicator in the complexometric and the water hardness determination. The intense color is due to the azo group, and the water solubility of the sulfonic acid group.

Properties

Aqueous solutions of Eriochrome black burgundy are up to a pH of 6. The sulfonic acid is deprotonated here and the two hydroxyl groups are protonated. By adding the two hydroxyl groups are deprotonated bases gradually and the solution turns blue at first. A further increase of the pH, a color change occurs to yellow. This Indikatoranionen now form with divalent metal ions a weak purple colored complex, which is destroyed by the addition of a stronger complexing agent such as EDTA again. To create a greater contrast at the transition point, Eriochrome black T is often used as a mixed indicator of methyl orange. This change of color from red to a gray intermediate tone done to green.