Stability Constants and Decay of Aqua‐Copper(III) – A Study by Pulse Radiolysis with Conductometric and Optical Detection

Abstract

Hydroxyl radicals were generated radiolytically in N2O-saturated aqueous solutions and reacted with Cu ions. Pulse radiolysis with conductometric detection showed that the aqua-CuIII species thus formed (k = 3.2 × 108 dm3 mol–1 s–1) is uncharged at pH 5, i.e. [Cu(OH)3]aq, and from the changes in conductance as a function of pH it has been calculated that Cu(OH) must have a pK value of 4.8 and Cu(OH) a value of 3.7. At pH 2.5 there is no strong evidence for the presence of Cu. Aqua-Cu(OH)3 decays bimolecularly to give Cu and H2O2. Cu(OH) [and possibly also Cu(OH)] are in equilibrium with Cu and OH radicals [K(Cu(OH)) ≈ 3.7 × 104 dm3 mol–1]. Rapid electron transfer occurs from Cu to [Cu(OH)3]aq (k = 3.5 × 109 dm3 mol–1 s–1).