Keywords
Metallochromic indicators
Eriochrome Black T
Indicator blocking
pH influence
End-point determination
Metrica
How to Cite
Abstract
Metallochromic indicators are chromophoric organic compounds capable of forming complexes with metal cations. The observed color change results from the transition between their free and complexed forms, a phenomenon governed by chemical equilibria dependent on parameters such as pH and the cation concentration in solution. This property, utilized for the visual detection of the endpoint in complexometric titrations, relies on the difference in stability between the metal-indicator and metal-titrant complexes, as well as on a detailed understanding of the chemical equilibria involved. From an experimental standpoint, in addition to the magnitude of the conditional stability constants, the choice of indicator must also consider selectivity for the cation of interest (analyte) and the pH range within which the system remains stable. Minute quantities of the indicator should be used to minimize equilibrium disturbances and ensure that the color transition occurs sharply and reproducibly at the titration endpoint.
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