Copper(II) hydroxide
Copper(II) hydroxide is the hydroxide of the metal copper with the chemical formula of Cu(OH)2. Copper hydroxide is a pale blue, gelatinous solid. Some forms of copper(II) hydroxide are sold as "stabilized" copper hydroxide, quite likely a mixture of copper(II) carbonate and hydroxide. These are often greener in colour. Copper hydroxide acts as a weak base in aqueous solution.
History
Copper(II) hydroxide has been known since copper smelting began around 5000 BC although the alchemists were probably the first to manufacture it. This was easily done by mixing solutions of lye (sodium or potassium hydroxide) and blue vitriol (copper(II) sulfate), both chemicals which were known 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.
Natural occurrence
Copper(II) hydroxide occurs naturally as a component of several copper minerals, notably azurite, malachite, antlerite, and brochantite. Azurite (2CuCO3·Cu(OH)2) and malachite (CuCO3·Cu(OH)2) are carbonates while antlerite (CuSO4·2Cu(OH)2) and brochantite (CuSO4·3Cu(OH)2) are sulfates. 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. The mineral of the formula Cu(OH)2 is called spertiniite.
