Is Copper(II) Hydroxide an Intermediate in the Formation of the Hydroxide Chloride and Hydroxide Nitrate of Copper(II)?

Abstract

Copper(II) hydroxide chloride, Cu(OH)_1.5Cl_0.5, and copper(II) hydroxide nitrate, Cu(OH)_1.5- (NO₃)_0.5, were precipitated by the stepwise addition of hydroxide to solutions containing Cu²⁺ at 10^-4 or 10^-3 M, and Cl ^- or NO₃^- at several concentrations between 10^-3 and 10^-1 M. The nature of the precipitates was confirmed by X-ray diffraction. pK_s0 values estimated from the pH for 50% precipitation were 16.9 for Cu(OH)_1.5Cl_0.5 and 16.0 for Cu(OH)_1.5(NO₃)_0.5. In each case, as OH^- was added to a solution which contained Cu²⁺ with Cl ^- or NO₃^-, the pH rose initially to that characteristic of the formation of amorphous Cu(OH)₂(pK_s0 = 17.8), but decreased again after further additions of hydroxide or on aging to that characteristic of the more stable hydroxide chloride or hydroxide nitrate. It is suggested that Cu(OH)₂ is an intermediate in the formation of Cu(OH)_1.5Cl_0.5 and Cu(OH)_1.5(NO₃)_0.5.