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1800-102-2727You 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
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.
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)
CaCO3(s) + H2CO4(aq) --> CaSO4(s) + H2O(aq) + CO2(g)
CaCO3(s) --> CaO(s) + CO2(g) |
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.
CaCO3(s) + H2O(I) + CO2(g) --> Ca(HCO3)2(aq)
Q 1. A sample of calcium carbonate is taken for a flame test, the colour of the flame obtained would be:
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:
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.
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) |
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.
Related Topics
Potassium |
Bleaching Powder-Bleaching powder Uses |
Sodium Hydrogencarbonate (NaHCO3) |
Calcium Hydroxide |
s-Block Elements |
Diagonal Relationship |