The Stability of the Copper(II)-Eriochrome Red B Complex and the Compleximetric Titration of Copper(II) Ion

Abstract

Values of the conditional stability constant of the copper(II)-Eriochrome Red B complex in aqueous solutions of pH 3–6 have been determined employing a cupric ion electrode. When the ionic strength of the solution is 0.01, the value of the second acidity constant (pk₂) of Eriochrome Red B is 6.28 and the logarithm of the stability constant of the copper complex, log k_CuHI, about 8.2. The complex can be used as an indicator in the ocapleximetric titration of cupric ion with EDTA at pH values from 4 to 8.