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Copper(II) carbonate
Copper(II) carbonate or cupric carbonate is a chemical compound with formula CuCO3. At ambient temperatures, it is an ionic solid (a salt) consisting of copper(II) cations Cu2+ and carbonate anions CO2−3.
This compound is rarely encountered because it is difficult to prepare and readily reacts with water moisture from the air. The terms "copper carbonate", "copper(II) carbonate", and "cupric carbonate" almost always refer (even in chemistry texts) to a basic copper carbonate (or copper(II) carbonate hydroxide), such as Cu2(OH)2CO3 (which occurs naturally as the mineral malachite) or Cu3(OH)2(CO3)2 (azurite). For this reason, the qualifier neutral may be used instead of "basic" to refer specifically to CuCO3.
Reactions that may be expected to yield CuCO3, such as mixing solutions of copper(II) sulfate CuSO4 and sodium carbonate in ambient conditions, yield instead a basic carbonate and CO2, due to the great affinity of the Cu2+ ion for the hydroxide anion HO−.
Thermal decomposition of the basic carbonate at atmospheric pressure yields copper(II) oxide rather than the carbonate.
In 1960, C. W. F. T. Pistorius claimed synthesis by heating basic copper carbonate at 180 °C (356 °F) in an atmosphere of carbon dioxide at 450 atm (46 MPa) and water at 50 atm (5.1 MPa) for 36 hours. The bulk of the products was well-crystallized malachite Cu2CO3(OH)2, but a small yield of a rhombohedral substance was also obtained, claimed to be CuCO3. However, this synthesis was apparently not reproduced.
Reliable synthesis of true copper(II) carbonate was reported for the first time in 1973 by Hartmut Ehrhardt et al. The compound was obtained as a gray powder, by heating basic copper carbonate in an atmosphere of carbon dioxide (produced by the decomposition of silver oxalate, Ag2C2O4) at 500 °C (932 °F) and 20,000 atm (2 GPa). The compound was determined to have a monoclinic structure.
The stability of dry CuCO3 depends critically on the partial pressure of carbon dioxide (pCO2). It is stable for months in dry air, but decomposes slowly into CuO and CO2 if pCO2 is less than 0.11 atm (11 kPa).
In the presence of water or moist air at 25 °C (77 °F), CuCO3 is stable only for pCO2 above 4.57 atm (463 kPa) and pH between about 4 and 8. Below that partial pressure, it reacts with water to form a basic carbonate (azurite, Cu3(CO3)2(OH)2).
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Copper(II) carbonate
Copper(II) carbonate or cupric carbonate is a chemical compound with formula CuCO3. At ambient temperatures, it is an ionic solid (a salt) consisting of copper(II) cations Cu2+ and carbonate anions CO2−3.
This compound is rarely encountered because it is difficult to prepare and readily reacts with water moisture from the air. The terms "copper carbonate", "copper(II) carbonate", and "cupric carbonate" almost always refer (even in chemistry texts) to a basic copper carbonate (or copper(II) carbonate hydroxide), such as Cu2(OH)2CO3 (which occurs naturally as the mineral malachite) or Cu3(OH)2(CO3)2 (azurite). For this reason, the qualifier neutral may be used instead of "basic" to refer specifically to CuCO3.
Reactions that may be expected to yield CuCO3, such as mixing solutions of copper(II) sulfate CuSO4 and sodium carbonate in ambient conditions, yield instead a basic carbonate and CO2, due to the great affinity of the Cu2+ ion for the hydroxide anion HO−.
Thermal decomposition of the basic carbonate at atmospheric pressure yields copper(II) oxide rather than the carbonate.
In 1960, C. W. F. T. Pistorius claimed synthesis by heating basic copper carbonate at 180 °C (356 °F) in an atmosphere of carbon dioxide at 450 atm (46 MPa) and water at 50 atm (5.1 MPa) for 36 hours. The bulk of the products was well-crystallized malachite Cu2CO3(OH)2, but a small yield of a rhombohedral substance was also obtained, claimed to be CuCO3. However, this synthesis was apparently not reproduced.
Reliable synthesis of true copper(II) carbonate was reported for the first time in 1973 by Hartmut Ehrhardt et al. The compound was obtained as a gray powder, by heating basic copper carbonate in an atmosphere of carbon dioxide (produced by the decomposition of silver oxalate, Ag2C2O4) at 500 °C (932 °F) and 20,000 atm (2 GPa). The compound was determined to have a monoclinic structure.
The stability of dry CuCO3 depends critically on the partial pressure of carbon dioxide (pCO2). It is stable for months in dry air, but decomposes slowly into CuO and CO2 if pCO2 is less than 0.11 atm (11 kPa).
In the presence of water or moist air at 25 °C (77 °F), CuCO3 is stable only for pCO2 above 4.57 atm (463 kPa) and pH between about 4 and 8. Below that partial pressure, it reacts with water to form a basic carbonate (azurite, Cu3(CO3)2(OH)2).