Copper(II) hydroxide

Copper(II) hydroxide is the hydroxide of copper with the chemical formula of Cu(OH)2. It is a pale greenish blue or bluish green solid. Some forms of copper(II) hydroxide are sold as 'stabilized' copper hydroxide, although they likely consist of a mixture of copper(II) carbonate and hydroxide. Copper hydroxide is a weak base. Copper(II) hydroxide is the hydroxide of copper with the chemical formula of Cu(OH)2. It is a pale greenish blue or bluish green solid. Some forms of copper(II) hydroxide are sold as 'stabilized' copper hydroxide, although they likely consist of a mixture of copper(II) carbonate and hydroxide. Copper hydroxide is a weak base. Copper(II) hydroxide has been known since copper smelting began around 5000 BC although the alchemists were probably the first to manufacture it by mixing solutions of lye (sodium or potassium hydroxide) and blue vitriol (copper(II) sulfate). Sources of both compounds were available in antiquity. It was produced on an industrial scale during the 17th and 18th centuries for use in pigments such as blue verditer and Bremen green. These pigments were used in ceramics and painting. Copper(II) hydroxide can be produced by adding a sodium hydroxide to a dilute solution of copper(II) sulfate (CuSO4·5H2O). The precipitate produced in this manner, however, often contains water and an appreciable amount of sodium hydroxide impurity. A purer product can be attained if ammonium chloride is added to the solution beforehand. Alternatively, copper hydroxide is readily made by electrolysis of water (containing a little electrolyte such as sodium sulfate, or magnesium sulfate) with a copper anode. The mineral of the formula Cu(OH)2 is called spertiniite. Copper(II) hydroxide is rarely found as an uncombined mineral because it slowly reacts with carbon dioxide from the atmosphere to form a basic copper(II) carbonate. Thus copper slowly acquires a dull green coating in moist air by the reaction: The green material is in principle a 1:1 mole mixture of Cu(OH)2 and CuCO3. This patina forms on bronze and other copper alloy statues such as the Statue of Liberty. The structure of Cu(OH)2 has been determined by X-ray crystallography The copper center is square pyramidal. Four Cu-O distances in the plane range are 1.96 Å, and the axial Cu-O distance is 2.36 Å. The hydroxide ligands in the plane are either doubly bridging or triply bridging. It is stable to about 100 °C. Copper(II) hydroxide reacts with a solution of ammonia to form a deep blue solution of tetramminecopper 2+ complex ion. It catalyzes the oxidation of ammonia solutions in presence of dioxygen, giving rise to copper ammine nitrites, such as Cu(NO2)2( NH3)n.