Spectrophotometric Study of Metal Chelates of Eriochrom Black T (BT). II. Solution Equilibria between BT and Lead(II)-Nitrilotriacetate (NTA) or Cadmium(II)-N′-(Hydroxyethyl)-ethylenediamine-N, N, N′-triacetate (EDTA-OH)

Abstract

The solution equilibria between BT and lead(II)-NTA or cadmium(II)-EDTA-OH chelates were studied spectrophotometrically, and the composition and the stability constants of the BT chelates of these metal ions were determined. In the presence of an excess amount of NTA or EDTA-OH, lead(II) and cadmium(II) ions join with BT to form a chelate with a 1-to-1 composition. The magnitude of the stability constants (1013.19 and 1012.74 respectively, μ=0.30) can explain satisfactorily the well-known experimental fact that BT can be used as a metallochromic indicator in Pb(II)- and Cd(II)-EDTA titrations.