Complexometric indicator

A dye that changes color when it binds metal ions, signaling the endpoint of a complexometric titration.

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Metallochromic indicator: A dye whose color changes when it coordinates metal ions. Complexometric indicators are metallochromic dyes used to reveal metal-ion binding during titration.
Calmagite: A metallochromic dye used to indicate hardness and other metal-ion titrations. It provides an alternative to Eriochrome Black T for magnesium and water-hardness endpoints.
Coordination chemistry: The study of compounds in which central atoms or ions bind surrounding molecules or ions. Indicator behavior rests on metal ions coordinating dye molecules and titrant ligands.
Potentiometric titration: A titration method that tracks electrode potential as titrant is added. It locates endpoints instrumentally instead of relying on a visible indicator color change.
Eriochrome Black T: A metallochromic dye used chiefly to indicate calcium and magnesium titrations. Its wine-red metal complex turns blue when EDTA captures the metal near the endpoint.
Murexide: A metallochromic indicator used in complexometric titrations, especially for calcium. Its color response is useful when calcium is titrated under strongly alkaline conditions.
Chelation: Coordination of a metal ion by a ligand that attaches through multiple donor atoms. Many titrants form chelate rings that outcompete the indicator for metal ions.
Redox indicator: A compound whose color changes as its oxidation state changes during a redox reaction. Its signal tracks electron transfer, unlike a complexometric indicator's metal-binding equilibrium.
EDTA: A multidentate ligand that forms stable complexes with many metal ions. EDTA displaces the indicator from its weaker metal complex as titration reaches completion.
Xylenol Orange: A metallochromic indicator used for complexometric titrations of several metal ions. It supports endpoints for metals such as bismuth and zinc in appropriately acidic solutions.