Properties of Carbonate Ion

The following are some properties of carbonate ions:

• At room temperature, carbonates exist in solid form.
• The carbonates of group-1 and group-2 elements are colorless, whereas the carbonates of transition elements are coloured.
• As the polarising power of the group-1 metal ions (M⁺) is less than that of group-2 metal ions (M²⁺), group-2 carbonates are more covalent than the carbonates of group-1.
• Upon heating, carbonates decompose into carbon dioxide and oxide.
• The carbonates of alkali metals are more stable than those of alkaline earth metals. So, the carbonates of alkaline earth metals decompose easily when heated.
• As we move down the group, the thermal stability of group-1 and group-2 carbonates increases.
• All the carbonates of group-1 elements are fairly soluble in water except for Li₂CO₃. As we move down the group, the solubility increases due to the increase in ionic nature.
• All the carbonates of group-2 elements are sparingly soluble in water, but they are fairly soluble in a solution of CO₂ because of the formation of bicarbonates.

A carbonate ion is the simplest oxocarbon anion and is a salt of carbonic acid. It is a polyatomic ion whose molecular formula is CO₃^2-. The term “carbonate” can also refer to a carbonate ester, which is an organic compound with the carbonate group C(=O)(O-)₂. Carbonates are widely used in industrial applications, like in the smelting of iron, as a raw material in the production of Portland cement and lime, in the composition of ceramic glazes, and more. Alkali and alkaline earth metals are the main groups of elements that are used as carbonates. The carbonates of alkali metals are more stable than those of alkaline earth metals. Chemically precipitated sedimentary rock has a wide variety of carbonate minerals. Some carbonate minerals that are present in nature are limestone (CaCO₃), dolomite (CaCO₃.MgCO₃), soda ash (Na₂CO₃), siderite (FeCO₃), witherite (BaCO₃), etc.