Copper(II) carbonate
Copper carbonate or cupric carbonate is a chemical compound with formula. At ambient temperatures, it is an ionic solid consisting of copper cations and carbonate anions.
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 carbonate", and "cupric carbonate" almost always refer to a basic copper carbonate, such as or . For this reason, the qualifier neutral may be used instead of "basic" to refer specifically to.
Preparation
Reactions that may be expected to yield, such as mixing solutions of copper(II) sulfate and sodium carbonate in ambient conditions, yield instead a basic carbonate and, due to the great affinity of the ion for the hydroxide anion.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 in an atmosphere of carbon dioxide at and water at for 36 hours. The bulk of the products was well-crystallized malachite, but a small yield of a rhombohedral substance was also obtained, claimed to be. However, this synthesis was apparently not reproduced.
Reliable synthesis of true copper 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 at and. The compound was determined to have a monoclinic structure.
Chemical and physical properties
The stability of dry depends critically on the partial pressure of carbon dioxide. It is stable for months in dry air, but decomposes slowly into and if is less than.In the presence of water or moist air at, is stable only for above and pH between about 4 and 8. Below that partial pressure, it reacts with water to form a basic carbonate.
In highly basic solutions, the complex anion is formed instead.
The solubility product of the true copper carbonate was measured by Reiterer and others as pKso = 11.45 ± 0.10 at.