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)1.5Cl0.5, 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. pKs0 values estimated from the pH for 50% precipitation were 16.9 for Cu(OH)1.5Cl0.5 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(pKs0 = 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)1.5Cl0.5 and Cu(OH)1.5(NO3)0.5.