Calcium Carbide - Definition, Structure, Formula, Uses with FAQs

Calcium Carbide

An important chemical compound with formula CaC₂ is known as calcium carbide or calcium acetylide. One of its industrial use is that it is used for the synthesize of acetylene and calcium cyanamide.

In the pure state, it is found to be colourless, but anyway, the pieces of technical grade of CaC₂ are grey or brown in colour and contain $80-85 \%$ of CaC₂. The rest of it is composed of CaO, Ca₃P₂, CaS, Ca₃N₂, SiC etc.

CaC₂ is mainly employed in the manufacture of acetylene gas and also to produce acetylene in carbide lamps. It is also used to synthesize various chemicals and fertilizers and is also involved in steel making.

Structure Of Calcium Carbide

Calcium carbide ( $\mathrm{CaC}_2$ ) is an ionic compound consisting of $\mathrm{Ca}^{2+}$ (calcium ion) and $\mathrm{C}_2{ }^{2-}$ (acetylide ion).

Structure

• Calcium loses two electrons to form $\mathrm{Ca}^{2+}$.
• The two carbon atoms gain these electrons and form the acetylide ion $\left(\mathrm{C}_2{ }^{2-}\right)$.
• The two carbon atoms are connected by a triple bond (C≡C).

Calcium Carbide formula

The calcium carbide formula is $\mathrm{CaC}_2$.

Preparation of Calcium Carbides

Calcium carbide is prepared commercially by heating quicklime (calcium oxide) with coke (carbon) in an electric furnace at a very high temperature of about 2000–2200°C. In this process, carbon reduces calcium oxide and combines with calcium to form calcium carbide.

Chemical Reaction

$\mathrm{CaO}+3 \mathrm{C} \rightarrow \mathrm{CaC}_2+\mathrm{CO}$

Process

• A mixture of calcium oxide (lime) and coke is fed into an electric arc furnace.
• The furnace provides the high temperature required for the reaction.
• Calcium carbide is formed as a molten mass, which is then cooled and collected.
• Carbon monoxide gas is produced as a by-product.

Also, students can refer,

• NCERT solutions for Class 12 Chemistry The S-Block Elements
• NCERT Exemplar Class 12 Chemistry Solutions The S-Block Elements
• NCERT notes Class 12 Chemistry The S-Block Elements

Applications of Calcium Carbide

• Production of Acetylene: CaC₂ reacts with water to form acetylene and calcium hydroxide.

$\mathrm{CaC}_{2(\mathrm{~S})}+2 \mathrm{H}_2 \mathrm{O}_{(\mathrm{aq})} \rightarrow \mathrm{C}_2 \mathrm{H}_{2(\mathrm{~g})}+\mathrm{Ca}(\mathrm{OH})_{2(\mathrm{aq})}$

• Production of calcium cyanamide: The reaction of CaC₂ with N₂ at a very high-temperature forms calcium cyanamide. It is generally known as nitrolime and is used as a fertilizer. It undergoes hydrolysis to form cyanamide H₂NCN.

$\mathrm{CaC}_2+\mathrm{N}_2 \rightarrow \mathrm{CaCN}_2+\mathrm{C}$

• Steel making: CaC₂ is used in the desulfurization of iron and also as a fuel in steelmaking to extend the scrap ratio to liquid iron.

• Deoxidizer: In ladle treatment it acts as a strong deoxidizer.

• As a ripening agent: CaC₂ is used as a source of acetylene gas which functions as an alternative ripening agent like ethylene.

• CaC₂ is also used to find out the moisture content of the soil.

• CaC₂ is nowadays sold as a mole repellent.

Related topics link,

• Sodium Oxide
• The Story of Washing Soda na2co3 10h2o
• potassium
• Sodium Thiosulfate
• Infrared Spectroscopy

Different Types of Carbide

On the basis of the bond present between the carbide ion and the metal element, carbides are generally of the following types.

• Ionic carbides- The combination of alkali or alkaline earth metals with carbide ions results in the formation of ionic carbides. The electrostatic attractive force binds these ions. There exists a huge electronegativity difference in this type of carbides. CaC₂ is an example.

• Covalent carbides- Low electropositive elements such as ‘Si’ and ‘B’ combines with carbide ions to form covalent carbides. In this type of carbides, there exists a low electronegativity difference. ‘SiC’ (Carborundum), B₄C are examples.

• Interstitial carbides- The combination of transition metals and carbide molecules forms interstitial carbides. In this type of carbide, carbide ions occupy the interstitial site of the metal lattice. TiC is an example.

• Intermediate transition metal carbide – These types of carbides are also composed of transition metal and carbide ion and their size is found to be similar. Carbide of iron or known as cementite (Fe₃C) is an example.

Uses of Carbides

• Most of the carbides are found to be very hard. So they are used as abrasive tools, drilling and cutting tools.

• They are used as reducing agents in metallurgy.

• Al₄C₃ is used to synthesize methane whereas CaC₂ is used for the manufacture of acetylene.

• Carbides are also employed as furnace lining.

• Boron carbide is generally used to cut diamond, to make filaments of lamps and also to drill holes in rocks.

• The carbide of tungsten is nowadays used in making jewellery and also in the manufacture of various surgical tools.

Also check-

Some Solved Examples

Question: In curing cement plaster, water is sprinkled from time to time. This helps in:

1) keeping it cool

2) (correct) developing interlocking needle­-like crystals of hydrated silicates

3) Hydrating sand and gravel mixed with cement

4) converting sand into silicic acid.

Solution:

Water helps in the hydration of calcium aluminates and calcium silicates, which change into their colloidal gels by developing interlocking needle-like crystals of hydrated silicates.

The hydrolysis leads to the formation of calcium hydroxide which is useful in binding the particles of calcium silicate together.

Hence, the answer is option (2).

Question 2: When calcium carbide reacts with water, the gas evolved is:

A) Ethylene
B) Acetylene
C) Methane
D) Ethane

Solution:

$\mathrm{CaC}_2+2 \mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{C}_2 \mathrm{H}_2+\mathrm{Ca}(\mathrm{OH})_2$

The gas produced is acetylene (C₂H₂).

Hence, the answer is option (2).

Question 3: Which of the following are true for $\mathrm{CaC}_2$?
1. Produced by heating lime and coke in an electric arc furnace.
2. Hydrolysis gives $\mathrm{C}_2 \mathrm{H}_2$.
3. $\mathrm{C}_2{ }^{2-}$ ion has a triple bond.
4. It is used to make calcium cyanamide.

A) 1, 2, 3
B) 2, 3, 4
C) 1, 2, 4
D) 1, 2, 3, 4

Solution:

All statements are correct. CaC₂ is a versatile industrial raw material.

Hence, the answer is option (4).

Question 4: When 6.4 g of CaC₂ reacts completely with water, the volume of acetylene obtained at STP (22.4 L/mol) is __ L.

1) 2.24L

2) 1.24L

3) 2.27L

4) 1.22L

Solution:

Molar mass $\mathrm{CaC}_2=64 \mathrm{~g} / \mathrm{mol}$.
Moles of $\mathrm{CaC}_2=6.4 / 64=0.1 \mathrm{~mol}$.
$1 \mathrm{~mol} \mathrm{CaC} \mathrm{C}_2 \rightarrow 1 \mathrm{~mol} \mathrm{C}_2 \mathrm{H}_2$.
So, $0.1 \mathrm{~mol} \rightarrow 0.1 \times 22.4=2.24 \mathrm{~L}$.

Hence, the answer is option (1).

Question 5: Calcium carbide reacts with water to produce acetylene gas. The volume of acetylene obtained at STP from 64 g of CaC₂ is:

(A) 11.2 L
(B) 22.4 L
(C) 44.8 L
(D) 5.6 L

Solution:

$\mathrm{CaC}_2+2 \mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{C}_2 \mathrm{H}_2+\mathrm{Ca}(\mathrm{OH})_2$

Molar mass of $\mathrm{CaC}_2=40+(12 \times 2)=\mathbf{6 4 ~ g} \mathbf{~ m o l}^{-\mathbf{1}}$

Therefore,
$64 \mathrm{~g} \mathrm{CaC}_2=1 \mathrm{~mol} \mathrm{CaC}_2$

From the balanced equation:
$1 \mathrm{~mol} \mathrm{CaC}_2 \rightarrow 1 \mathrm{~mol} \mathrm{C}_2 \mathrm{H}_2$

At STP,

1 mol gas $=22.4 \mathrm{~L}$

Hence,
$1 \mathrm{~mol} \mathrm{C}_2 \mathrm{H}_2=22.4 \mathrm{~L}$

Hence, the correct answer is option (B)

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