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 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.

Structure of Carbonate Ion

A carbonate ion is the simplest oxocarbon anion, where a carbon atom is surrounded by three oxygen atoms. This has a trigonal planar arrangement with D_3h molecular symmetry. The Lewis structure of a carbonate ion has two long single bonds to negatively charged oxygen atoms and a short double bond to a neutral oxygen atom.

Carbonate ion structure

Properties of Carbonate Ion

Chemical Formula	CO32−
IUPAC Name	Carbonate
Molar Mass	60.008 g/mol
Conjugate Acid	Bicarbonate

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.

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 + O^2-  (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.

CO₃^2- + 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

Uses of Carbonates

• 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.
• They are also used in the manufacturing of glass. 
• In washing detergents, carbonates like sodium and potassium carbonate are used.
• Carbonates are also used to soften water.

FAQs on Carbonate Ion Formula

Question 1: What is a carbonate ion?

Answer:

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-. Some examples of carbonates are Li₂CO₃, Na₂CO₃, MgCO₃, CaCO₃, FeCO_3, and so on.

Question 2: Describe the structure of a carbonate ion.

Answer:

A carbonate ion is the simplest oxocarbon anion, where a carbon atom is surrounded by three oxygen atoms. This has a trigonal planar arrangement with D3h molecular symmetry. The Lewis structure of a carbonate ion has two long single bonds to negatively charged oxygen atoms and a short double bond to a neutral oxygen atom.

Question 3: Mention some properties of carbonates.

Answer:

The molar mass of a carbonate ion is 60.008 g/mol and its conjugate acid is bicarbonate. 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 colored. 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.

Question 4: Mention some uses of carbonates.

Answer:

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. They are also used in the manufacturing of glass. In washing detergents, carbonates like sodium and potassium carbonate are used. Carbonates are also used to soften water.

Question 5: Write the calcination reaction.

Answer:

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)

Question 6: Write about the solubility of carbonates in the water.

Answer:

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.