Basic copper carbonate

Basic copper carbonate is a chemical compound, more properly called copper(II) carbonate hydroxide. It is an ionic compound (a salt) consisting of the ions copper(II) Cu2+, carbonate CO32-, and hydroxide OH-. The name most commonly refers to the compound with formula Cu2CO3(OH)2. It is a green crystalline solid that occurs in nature as the mineral malachite. It has been used since antiquity as a pigment, and it is still used as such in artist paints, sometimes called verditer, green bice, or mountain green. Sometimes the name is used for Cu3(CO3)2(OH)2, a blue crystalline solid also known as the mineral azurite. It too has been used as pigment, sometimes under the name mountain blue or blue verditer. Both malachite and azurite can be found in the verdigris patina that is found on weathered brass, bronze, and copper. The composition of the patina can vary, in a maritime environment depending on the environment a basic chloride may be present, in an urban environment basic sulfates may be present. This compound is often improperly called (even in chemistry articles) copper carbonate, cupric carbonate, and similar names. The true (neutral) copper(II) carbonate CuCO3 is not known to occur naturally. It is decomposed by water or moisture from the air, and was synthesized only in 1973 by high temperature and very high pressures. Basic copper carbonate is prepared by combining aqueous solutions of copper(II) sulfate and sodium carbonate at ambient temperature and pressure. Basic copper carbonate precipitates from the solution, with release of carbon dioxide CO2: 2 CuSO4 + 2 Na2CO3 + H2O → Cu2(OH)2CO3 + 2 Na2SO4 + CO2 Basic copper carbonate can also be prepared by reacting aqueous solutions of copper(II) sulfate and sodium bicarbonate at ambient conditions. Basic copper carbonate precipitates from the solution, again with release of carbon dioxide: 2 CuSO4 + 4 NaHCO3 → Cu2(OH)2CO3 + 2 Na2SO4 + 3 CO2 + H2O Copper(II) sulfate may also be substituted with Copper(II) chloride, creating Sodium chloride (NaCl) as a byproduct instead of Sodium sulfate (Na2SO4), both of which are soluble in water.