Eriochrome Black T indicator
Description
Eriochrome Black T is a dark purple-brown or black azo dye commonly used as a complexometric indicator in analytical chemistry, especially to determine water hardness via EDTA titration.
Chemical Properties
Molecular formula: C₆₀H₁₂N₃O₇SNa
Molar mass: 461.38 g/mol
Appears as a dark red-brown or black powder; odorless.
Soluble in water (5 g/100 ml at 20°C) but nearly insoluble in most organic solvents including ethanol.
pKa values: ~6.2 and 11.55 (for acid dissociation).
Indicator Function
In EDTA titration, Eriochrome Black T binds metal ions such as Ca²⁺ and Mg²⁺, turning red when complexed.
When all metal ions are chelated by EDTA, the indicator reverts to its unbound blue form, marking the titration endpoint.
It’s also used to detect rare earth metals and can serve in test paper preparation for calcium detection.
Safety and Storage
Irritant but not considered highly toxic or carcinogenic; ingestion may cause diarrhea.
Store in closed amber bottles, away from light and corrosive vapors to preserve stability.
Eriochrome Black T is fundamental in water quality assessment and general complexometric analysis due to its distinct color change and reliable sensitivity to metal ions.
Specifications
| Model No. | N-CH1756 |
|---|
