14.4 COMPLEXES OF Cu(l)
The chloride complexes of Cu(I) are given by Reactions 43 through 46 of
Table 14.1. These complexes are plotted in Fig. 14.8 in equilibrium with
cuprous ferrite at pH 11.53. This is the redox at which soil-F e and magnetite
can coexist. The activities of Cu J' and Cuz “L are included for comparison. At
this selected redox CuCl? and CuCl complexes approach that of Cu*
if Cl' is near 10"3 M. The CuCl ` complex requires > 10” z M Cl' to equal
Cu“`. At pe -|~ pH 11.53 the sum of all Cu(I) species is less than that of Cuz T.
As redox rises. the Cuz J' line rises (equilibrium with ferrous ferrite and soil-Fe).
Above pe + pH 14.89 copper is controlled by soil-Cu and Cuz* activity is
no longer redox dependent. As redox drops below pe + pH of 11.53. C u*
and its accompanying Cl” complexes (in equilibrium with cuprous ferrite
and magnetite) increase while Cuz+ decreases. Thus the Cu(I) complexes in
solution can exceed the Cu(II) species as redox drops.