Formula Cu(OH)2 Density 3.37 g/cm³ | Molar mass 97.561 g/mol Melting point 80 °C | |
Appearance Blue or blue-green solid Related compounds | ||
Copper ii hydroxide redissolve in excess ammonium
Copper(II) hydroxide is the hydroxide of the metal copper with the chemical formula of Cu(OH)2. Copper hydroxide is a pale blue 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.
Contents
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.
Synthesis
Copper(II) hydroxide can be produced by adding a small amount of sodium hydroxide to a dilute solution of copper(II) sulfate (CuSO4 · 5H2O). The precipitate produced in this manner, however, often contains water molecules and an appreciable amount of sodium hydroxide impurity. A purer product can be attained if ammonium chloride is added to the solution beforehand. Nevertheless, it is impossible to obtain a pure product; processes for eliminating impurities lead to the destruction of the hydroxide, giving rise to the more stable oxide, CuO. Alternatively, copper hydroxide is readily made by electrolysis of water (containing a little electrolyte such as sodium sulfate, or magnesium sulfate). A copper anode is used, often made from scrap copper.
Copper slowly acquires a dull green coating in moist air by the reaction:
2 Cu (s) + H2O (g) + CO2 (g) + O2 (g) → Cu(OH)2 (s) + CuCO3 (s)Thus the green material is a 1:1 mole mixture of Cu(OH)2 and CuCO3. This is the patina that forms on bronze and other copper alloy statues such as the Statue of Liberty.
Reactions
Moist samples of copper(II) hydroxide slowly turn black due to the formation of copper(II) oxide. When it is dry, however, copper(II) hydroxide does not decompose unless it is heated to 185 °C.
Copper(II) hydroxide reacts with a solution of ammonia to form a deep blue solution of tetramminecopper [Cu(NH3)4]2+ complex ion. Copper(II) hydroxide in ammonia solution, known as Schweizer's reagent, possesses the interesting ability to dissolve cellulose. This property led to it being used in the production of rayon, a cellulose fiber. It is also used widely in the aquarium industry for its ability to destroy external parasites in fish, including flukes, marine ich, brook and marine velvet, without killing the fish. Although other water-soluble copper compounds can be effective in this role, they generally result in high fish mortality. Cupramine is also widely used in organic chemical synthesis, discussed below.
Besides, when the concentration of ammonia solutions is very high, divalent copper ions in presence of dioxygen, catalyze ammonia oxidation, giving rise to copper ammine nitrites: Cu (NO2)2( NH3)n;
Since copper(II) hydroxide is mildly amphoteric, it dissolves slightly in concentrated alkali, forming [Cu(OH)4]2−.
Reagent for organic chemistry
Copper(II) hydroxide has a rather specialized role in organic synthesis. Often, when it is utilized for this purpose, it is prepared in situ by mixing a soluble copper(II) salt and potassium hydroxide.
It is sometimes used in the synthesis of aryl amines. For example, copper(II) hydroxide catalyzes the reaction of ethylenediamine with 1-bromoanthraquinone or 1-amino-4-bromoanthraquinone to form 1-((2-aminoethyl)amino)anthraquinone or 1-amino-4-((2-aminoethyl)amino)anthraquinone, respectively:
Copper(II) hydroxide also converts acid hydrazides to carboxylic acids at room temperature. This is especially useful in synthesizing carboxylic acids with other fragile functional groups. The published yields are generally excellent as is the case with the production of benzoic acid and octanoic acid:
Uses
Copper(II) hydroxide has been used as an alternative to the Bordeaux mixture, a fungicide and nematicide. Such products include Kocide 3000, produced by Kocide L.L.C. Copper(II) hydroxide is also occasionally used as ceramic colorant.
Copper(II) hydroxide has been combined with latex paint, making a product designed to control root growth in potted plants. Secondary and lateral roots thrive and expand, resulting in a dense and healthy root system. It was sold under the name Spin Out, which was first introduced by Griffin L.L.C. The rights are now owned by SePRO Corp. It is now sold as Microkote either in a solution you apply yourself, or as treated pots.