Chemical Properties
A carbonate salt is formed when a positively charged ion, such as M+, M2+, or M3+, forms an electrostatic attraction with the negatively charged oxygen atoms of the carbonate ion to form an ionic compound.
For example, 2 moles of M3+ ion react with 3 moles of carbonate ion to form a mole of M2(CO3)3.
2M3++ 3CO32− → M2(CO3)3
Carbonates of group-1 elements (alkali metals) |
2M++ CO32−→ M2CO3 | Li2CO3, Na2CO3, K2CO3, etc., |
---|---|---|
Carbonates of group-2 elements (alkaline earth metals) |
M2++ CO32− → MCO3 | MgCO3, CaCO3, BaCO3, etc., |
Carbonates of p-block elements |
— |
Tl2CO3 and PbCO3 |
Carbonates of transition elements |
— |
ZnCO3, CuCO3, Ag2CO3, FeCO3, etc.,. |
- Upon heating, carbonates decompose into carbon dioxide and oxide.
CO32−→ CO2 + O2- (On heating)
For example, when calcium carbonate is heated, it liberates carbon dioxide, leaving behind calcium oxide, or quick lime (CaO). This process is known as calcination and is used to get CaO in lime kilns. When quick lime (CaO) is combined with water, it produces slaked lime (Ca(OH)2).
CaCO3 → CaO + CO2 (On heating)
- When carbonate ion reacts with acidic solutions carbon dioxide and water is formed.
CO32- + 2H+ → CO2 + H2O (in acidic medium)
For example, when weak hydrochloric acid comes into contact with limestone (CaCO3), it causes fizz. Or the effervescence that is observed when lime juice is dropped on the floor leaves a white mark because of the citric acid present in lime juice.
CaCO3 + 2HCl → CaCl2 + H2O + CO2
MgCO3 + 2HCl → MgCl2 + H2O + CO2
Carbonate Ion Formula
A carbonate ion is the simplest oxocarbon anion and is a salt of carbonic acid. It is a polyatomic ion whose molecular formula is CO32-. 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.