Eriochrome Black T is a
complexometric indicator
A complexometric indicator is an ionochromic dye that undergoes a definite color change in presence of specific metal ions. It forms a weak complex with the ions present in the solution, which has a significantly different color from the form ex ...
that is used in
complexometric titration
Complexometric titration (sometimes chelatometry) is a form of volumetric analysis in which the formation of a colored complex is used to indicate the end point of a titration. Complexometric titrations are particularly useful for the determinati ...
s, e.g. in the
water hardness determination process. It is an
azo dye. Eriochrome is a trademark of
Huntsman Petrochemical, LLC.
In its deprotonated form, Eriochrome Black T is blue. It turns red when it forms a
complex
Complex commonly refers to:
* Complexity, the behaviour of a system whose components interact in multiple ways so possible interactions are difficult to describe
** Complex system, a system composed of many components which may interact with each ...
with
calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar t ...
,
magnesium
Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
, or other metal ions.
Applications
When used as an indicator in an
EDTA
Ethylenediaminetetraacetic acid (EDTA) is an aminopolycarboxylic acid with the formula H2N(CH2CO2H)2sub>2. This white, water-soluble solid is widely used to bind to iron (Fe2+/Fe3+) and calcium ions (Ca2+), forming water-soluble complexes ev ...
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.
References
{{Reflist
External links
J.T. Baker MSDS
Complexometric indicators
Titration
Analytical chemistry
Azo dyes
1-Naphthols
2-Naphthols
Nitronaphthalenes
Naphthalenesulfonates
Organic sodium salts