Calcium Carbonate-Formula, Structure, Properties, Preparation, Uses, Practice Problems, and FAQs

You must have seen those beautiful pearls or jewellery made with pearls, gracefully enhancing the beauty of anyone putting it on. Have you ever wondered what it is actually made of?

Well, the answer is calcium carbonate, hidden inside the oyster shells. Calcium carbonate is an inorganic compound having the molecular formula CaCO₃.

It is commonly found in the earth’s crust. It is available in different forms such as limestone, marble, calcite, aragonite etc. Calcium carbonate is available in naturally occurring forms like aragonite, vaterite, calcite and industrial forms include limestone, marble, chalk and travertine, and oyster shells.

TABLE OF CONTENTS

Structure of Calcium Carbonate
Preparation of Calcium Carbonate
Properties of Calcium Carbonate
Uses of Calcium Carbonate
Practice Problems
Frequently Asked Questions-FAQs

Structure of Calcium Carbonate

CaCO₃ comprises of two type of ions [Ca]²⁺& [CO₃]^2-where there is ionic bond between these two ions. Moreover, if you look at the carbonate ion, you will see it has a triangular planar structure.

The structure of calcite is a stable hexagonal β- structure, i.e. β- CaCO₃. Other forms of calcium carbonate include orthorhombic λ- CaCO₃ which is aragonite mineral and hexagonal μ- CaCO₃, which is a vaterite mineral.

Preparation of Calcium Carbonate

Calcium carbonate is commonly prepared by the following methods:

Method 1: Mostly, a large amount of calcium carbonate is obtained by mining or quarrying. The pure form of calcium carbonate is extracted by quarrying from pure sources like limestone.

Method 2: Calcium carbonate is prepared with the help of calcium oxide. Calcium oxide is reacted with water to give calcium hydroxide. The product thus formed is treated with carbon dioxide to form calcium carbonate. It is obtained by precipitating the solution.

CaO(s) + H₂O(aq) --> Ca(OH)₂(aq)

Ca(OH)₂(aq) + CO₂(g) --> CaCO₂(s) | + H₂O(aq)

Method 3: On a large scale, Calcium carbonate is obtained as a product of slaked lime, Ca(OH)₂ and carbon dioxide. On passing carbon dioxide through slaked lime, calcite is obtained as a product which is a form of calcium carbonate.

Ca(OH)₂(aq) + CO₂(g) --> CaCO₃(s) | + H₂O(aq)

Method 4: Calcium carbonate is obtained as calcite using another method. In this method, calcium chloride is used. Calcium chloride is added to sodium carbonate to obtain calcium carbonate in calcite form.

CaCI₂(s) + Na₂CO₃(s) --> CaCO₃(s) + 2NaCI(s)

Properties of Calcium Carbonate

Calcium carbonate is a white fluffy powder.
It decomposes on reaction with acids and releases carbon dioxide.

CaCO₃(s) + H₂CO₄(aq) --> CaSO₄(s) + H₂O(aq) + CO₂(g)

On thermal decomposition at 1200 K, it gives calcium oxide as a product. Calcium oxide is also called quick lime. The process of decomposition to give calcium oxide is called calcination.

CaCO₃(s) --> CaO(s) + CO₂(g) |

It reacts with water in presence of carbon dioxide in air, to give calcium bicarbonate.

CaCO₃(s) + H₂O(I) + CO₂(g) --> Ca(HCO₃)₂(aq)

The reaction of calcium carbonate and water results in the formation of hard water and is responsible for erosion.

The hexahydrate form of calcium carbonate CaCO₃. 6H₂O is known as ikaite, which is stable above 80°C temperature.
Calcium carbonate is sparingly soluble in water. Calcium bicarbonate Ca(HCO₃)₂ is however many times more soluble than calcium carbonate and when calcium carbonate comes in contact with water in the presence of CO₂ it changes into calcium bicarbonate and becomes more soluble in water.

CaCO₃(s) + H₂O(I) + CO₂(g) --> Ca(HCO₃)₂(aq)

Uses of Calcium Carbonate

Calcium carbonate is largely employed in the pulp and paper industry. It can be used as a filter and pigment, making possible the production of a whiter, higher quality pigment than other minerals.
In the construction industry, calcium carbonate is used as a filler in concrete, increasing its durability and appearance. Moreover, used in purifying metals which are used in construction applications.
In water and sewer treatment plants, calcium carbonate is employed in the removal of acidity and impurities.
It is also used to treat the acidic condition of soil and water. Liming is practised on a large scale to neutralize lakes and streams.
It is also useful in eliminating sulphur dioxide and nitrogen dioxide emissions from burning coal and other fossil fuels.
It is used for household purposes. Calcium carbonate is used in the manufacturing of detergents and other cleaning agents. Calcium carbonate is also beneficial as a scrubbing agent.
It is used extensively in agriculture. Calcium carbonate is responsible for the neutralization of the soil making it ideal for planting.
It is used in the aquaculture industry to maintain the of water bodies that are required for breeding.
It is used for dietary and medicinal purposes. Calcium carbonate is medicinally beneficial in producing calcium supplements.
It finds usage in the making of antacids and inert filler for tablets.
It is used in food preservatives and colour retainers.
It is also used to produce calcium oxide, which is used in the production of toothpaste.
It also acts as a phosphate binder in the treatment of hyperphosphatemia and to maintain haemodialysis.

Practice Problem

Q 1. A sample of calcium carbonate is taken for a flame test, the colour of the flame obtained would be:

Carmine red
Lilac
Yellowish green
Brick red

Answer: (D)
Flame test is an analytical test used to detect the presence of certain metal ions. Calcium carbonate contains Ca²⁺ which imparts brick red colour to the flame.

Q 2. What is the equivalent mass of CaCO₃?

Answer: Molar mass of CaCO₃ = [40 + 12 + (3 x 16)] = 100 g mol^-1

n - factor of CaCO₃ = 2

(Since CaCO₃ when broken into ions it form [ca]²⁺ and [CO₃]^2-. So, both have a valency of 2)

So, Equivalent mass of CaCO₃ = = 50 g eq^-1

Q 3. The types of bond in calcium carbonate is/are:

Ionic bond only
Covalent and Ionic bonds
Coordinate and Covalent bonds
Hydrogen and Covalent bonds

Answer: (B)
It is composed of two oppositely charged ions [Ca]²⁺ and [CO₃]^2-having electrostatic force of attraction between the two. So, ionic bond is there between these two ions to form CaCO₃. But if you look at the structure of carbonate ion [CO₃]^2-

You can see the covalent bonds in between carbon and oxygen atoms. So calcium carbonate consists of both ionic and covalent bonds.

Q 4. Choose the correct products of the reaction of limestone with dilute hydrochloric acid.

Ca, CI₂, H₂O and CO₂
CaCI₂, H₂O and CO₂
CaO, CaCI₂, H₂O and CO₂
CaO, CI₂, H₂O and CO₂

Answer: (B)
Limestone reacts with hydrochloric acid to produce its corresponding salt and gives of carbon dioxide gas along with water.

CaCO₃(s) + 2HCI(aq) --> CaCI₂(s) + H₂O(aq) + CO₂(g) |

Frequently Asked Questions-FAQs

Question 1. Is Limestone and calcium carbonate the same?
Answer: Yes. both are exactly the same with the formula CaCO₃.

Question 2. What is the difference between slaked lime, quick lime and limestone?
Answer: Quicklime or lime is CaO, Slaked lime is Ca(OH)₂ and Limestone is CaCO₃. All three can be easily converted into each other as shown in the figure below:

Question 3. How can we identify a carbonate salt?
Answer: A sample containing calcium carbonate or any carbonate salt, will produce fizz or effervescence on the addition of a strong acid such as HCI or H₂SO₄. This is due to the release of carbon dioxide.

CaCO₃(s) + 2HCI(aq) --> CaCI₂(s) + H₂O(aq) + CO₂(g) |

Question 4. What are the natural sources of calcium carbonate?
Answer: Calcium carbonate is a natural constituent of eggshells, shells of snails, seashells and pearls. It is also one of the components of dark green vegetables, which have good amounts of calcium carbonate. Medicinally, it finds great usage in calcium supplements and antacids.