Editing Module:Carbonate (section)

==Chemical properties==
[[image:Labeled speleothems (cropped).jpg|right|thumb|190px|Stalactites and stalagmites are carbonate minerals.]]
Metal carbonates generally decompose on heating, liberating carbon dioxide leaving behind an oxide of the metal.<ref name=EB1911/> This process is called [[calcination]], after ''calx'', the Latin name of quicklime or [[calcium oxide]], CaO, which is obtained by roasting limestone in a [[lime kiln]]:
:{{chem2|CaCO3 → CaO + CO2}}
As illustrated by its affinity for {{chem2|Ca(2+)}}, carbonate is a ligand for many metal cations. [[Transition metal carbonate and bicarbonate complexes]] feature metal ions covalently bonded to carbonate in a variety of bonding modes.

[[Lithium carbonate|Lithium]], [[sodium carbonate|sodium]], [[potassium carbonate|potassium]], [[rubidium carbonate|rubidium]], [[caesium carbonate|caesium]], and [[ammonium carbonate|ammonium]] carbonates are water-soluble salts, but carbonates of 2+ and 3+ ions are often poorly soluble in water. Of the insoluble metal carbonates, [[calcium carbonate|{{chem2|CaCO3}}]] is important because, in the form of [[limescale|scale]], it accumulates in and impedes flow through pipes. [[Hard water]] is rich in this material, giving rise to the need for infrastructural [[water softening]].

Acidification of carbonates generally liberates [[carbon dioxide]]:
:{{chem2|CaCO3 + 2 HCl → CaCl2 + CO2 + H2O}}
Thus, scale can be removed with acid.

In solution the equilibrium between carbonate, bicarbonate, carbon dioxide and carbonic acid is sensitive to pH, temperature, and pressure. Although di- and trivalent carbonates have low solubility, bicarbonate salts are far more soluble. This difference is related to the disparate [[lattice energy|lattice energies]] of solids composed of mono- vs dianions, as well as mono- vs dications.

In [[aqueous solution]], carbonate, bicarbonate, carbon dioxide, and carbonic acid participate in a [[chemical equilibrium|dynamic equilibrium]]. In strongly basic conditions, the carbonate ion predominates, while in weakly basic conditions, the [[bicarbonate]] ion is prevalent. In more acid conditions, aqueous [[carbon dioxide]], {{chem2|CO2(aq)}}, is the main form, which, with water, {{chem2|H2O}}, is in equilibrium with carbonic acid{{snd}}the equilibrium lies strongly towards carbon dioxide. Thus [[sodium carbonate]] is basic, [[sodium bicarbonate]] is weakly basic, while carbon dioxide itself is a weak acid.