Carbonate Ion Formula

A carbonate is a salt of carbonic acid (H$${}_2$$CO$${}_3$$) that is distinguished by the presence of the carbonate ion (a polyatomic ion). The carbonate formula is CO$${}_3^{-2}$$ in Chemistry.

A carbonate ester, an organic molecule bearing the carbonate group C(= O)(O$${}^{-}$$)$${}_2$$ , may also be referred to by this term.

Carbonated water and other carbonated beverages are made by increasing the concentrations of carbonate and bicarbonate ions in water, either by adding carbon dioxide gas under pressure or by dissolving carbonate or bicarbonate salts into the water.

Carbonate minerals and carbonate rock (which is primarily made up of carbonate minerals) are both dominated by the carbonate ion, CO$${}_3^{-2}$$. In chemically precipitated sedimentary rock, carbonate minerals are abundant and diverse. Calcite, or calcium carbonate, CaCO$${}_3$$, is the primary component of limestone (as well as mollusk shells and coral skeletons); dolomite, a calcium-magnesium carbonate CaMg(CO$${}_3$$)$${}_2$$; and siderite, or iron(II) carbonate, FeCO$${}_3$$, is an important iron resource. Since antiquity, sodium carbonate ("soda" or "natron") and potassium carbonate ("potash") have been used for cleaning, preservation, and the production of glass. Carbonates are widely utilised in industry, including in iron smelting, as a raw ingredient in the making of Portland cement and lime, and the composition of ceramic glazes, among other things.

Structure of Carbonate

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As we know the carbonate chemical formula, its structure can be easily drawn on the basis of it. The structure of carbonate ion is the simplest oxocarbon anion. It has D3h molecular symmetry and is made up of one carbon atom surrounded by three oxygen atoms in a trigonal planar arrangement. It has a total formal charge of 2 and a molecular mass of 60.01 g/mol. HCO$${}_3$$, the conjugate base of H$${}_2$$CO$${}_3$$ Carbonic acid is the conjugate base of the hydrogen carbonate (bicarbonate) ion.

The carbonate ion has two (long) single bonds to negative oxygen atoms and one short double bond to neutral oxygen in its Lewis structure.

Simple, localised Lewis structure of the carbonate ion

This structure contradicts the ion's observed symmetry, which predicts that the three bonds are all the same length and that the three oxygen atoms are all the same. Symmetry can be attained through a resonance among three structures, as in the example of the isoelectronic nitrate ion.

A model with fractional bonds and delocalized charges can be used to summarise this resonance:

Properties of Carbonate

On heating, metal carbonates disintegrate, releasing carbon dioxide from the long-term carbon cycle into the short-term carbon cycle and leaving behind a metal oxide. Calcination is named after calx, the Latin term for quicklime or calcium oxide (CaO), which is made by roasting limestone in a lime kiln.

A carbonate salt is formed when a positively charged ion, M$${}^{+}$$, M$${}^{+2}$$, or M$${}^{+3}$$, develops electrostatic interaction with the negatively charged oxygen atoms of the ion, generating an ionic compound:

2M$${}^{+}$$ + CO$${}_3^{-2}$$ → M$${}_2$$CO$${}_3$$

→ M$${}^{+2}$$ + CO$${}_3^{-2}$$ → MCO$${}_3$$

2M$${}^{+3}$$ + 3CO$${}_3^{-2}$$ → M$${}_2$$(CO$${}_3$$)$${}_3$$ 

At standard temperature and pressure, most carbonate salts are insoluble in water, with solubility constants of less than 1108. Lithium, sodium, potassium, and ammonium carbonates, as well as numerous uranium carbonates, are exceptions.

Carbonate, bicarbonate, carbon dioxide, and carbonic acid coexist in an aqueous solution in a dynamic equilibrium. The carbonate ion predominates in very basic environments, whereas the bicarbonate ion predominates in slightly basic circumstances. In more acidic settings, aqueous carbon dioxide, CO$${}_2$$(aq), is the predominant form, which is in equilibrium with carbonic acid when combined with water, H$${}_2$$O^–. The equilibrium is heavily skewed in favour of carbon dioxide. As a result, sodium carbonate is basic, sodium bicarbonate is slightly basic, and carbon dioxide is a weak acid in its own right.

When the partial pressure of CO$${}_2$$ is reduced, like when a can of soda is opened, the equilibrium shifts for each type of carbonate (carbonate, bicarbonate, carbon dioxide, and carbonic acid) until the concentration of CO$${}_2$$ in the solution equals the solubility of CO$${}_2$$ at that temperature and pressure. Carbonic anhydrase, an enzyme found in living systems, accelerates the conversion of CO$${}_2$$ to carbonic acid.

The balance between carbonate, bicarbonate, carbon dioxide and carbonic acid in solution is continually shifting due to variations in temperature and pressure. When metal ions interact with insoluble carbonates, such as CaCO$${}_3$$, insoluble compounds are formed. Hard water causes scale building inside pipes, which can be explained in this way.

Did You Know?

• Carbonated water is made by dissolving CO$${}_2$$ under pressure in water.

• Although the carbonate ions of most metals are insoluble in water, the bicarbonate salts are not.