Basic copper carbonate
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Through Salt (chemistry), Copper and Hydroxide
Sometimes basic copper carbonate refers to Cu
3(CO
3)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. It was synthesized only in 1973 by high temperature and very high pressures.
Preparation
Basic copper carbonate is prepared by combining aqueous solutions of copper(II) sulfate and sodium carbonate. Basic copper carbonate precipitates from the solution, with release of carbon dioxide CO
2:
- 2CuSO4 + 2Na2CO3 + H2O → Cu2(OH)2CO3 + 2Na2SO4 + CO2
Basic copper carbonate can also be prepared by treating aqueous solutions of copper(II) sulfate with sodium bicarbonate.
Copper(II) sulfate may also be substituted with Copper(II) chloride.
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Reactions
Basic copper carbonate is decomposed by acids, such as solutions of hydrochloric acid HCl, into the copper(II) salt and carbon dioxide.
In 1794 the French chemist Joseph Louis Proust (1754–1826) thermally decomposed copper carbonate to CO2 and CuO, cupric oxide.
The basic copper carbonates, malachite and azurite, both decompose forming H2O, CO2, and CuO, cupric oxide.
Uses
Basic copper carbonate is used to remove thiols and hydrogen sulfide from some gas streams, a process called "sweetening". Like many other copper compounds, it also has been used as an algaecide, wood preservative and similar applications. It is a precursor to various catalysts and copper soaps.
Both malachite and azurite, as well as synthetic basic copper carbonate have been used as pigments. One example of the use of both azurite and its artificial form blue verditer is the portrait of the family of Balthasar Gerbier by Peter Paul Rubens. The green skirt of Deborah Kip is painted in azurite, smalt, blue verditer (artificial form of azurite), yellow ochre, lead-tin-yellow and yellow lake. The green color is achieved by mixing blue and yellow pigments.