Alkanes Organic Chemistry Class-10 Concise Exe-12B Chemistry Selina ICSE Solutions Chapter-12. We Provide Step by Step Answer of Exe-12(B) Alkanes Questions of Exercise-12 for ICSE Class-10. The given Solutions is according to the Latest editions. Visit official Website CISCE for detail information about ICSE Board Class-10.

Alkanes Organic Chemistry Class-10 Concise Exe-12B Chemistry Selina ICSE Solutions Chapter-12

Board	ICSE
Book / Publication	Concise / Selina
Subject	Chemistry
Class	10th
Writer	Dr SP Singh
Chapter-12	Organic Chemistry
Exe-12B	Solved Questions on Alkanes
Edition	2025-2026

Solved Questions on Alkanes

Alkanes Organic Chemistry Class-10 Concise Exe-12B Chemistry Selina ICSE Solutions Chapter-12

Page-209

Que-1: State the sources of alkanes.

Ans: Sources of alkane:
The principal sources of alkanes are Natural gas and petroleum.

Que-2: Methane is a green house gas. Comment.

Ans: Methane is a primary constituent of natural gas. It absorbs outgoing heat radiation from the earth, and thus contributes to the green house effect and so it is considered as a green house gas.

Que-3: Give the general formula of alkanes.

Ans: The general formula of alkane is :
C_nH _2n+2

Que-4: Draw the structures of isomers of

(a) Butane (b) Pentane
Write the IUPAC and common names of these isomers

Ans: 
(a)The structures of isomers of butane are:
(i)

Common name:- n-Butane
IUPAC name:- Butane
(ii)

Common name:-iso butane
IUPAC name:- 2-methyl propane
(b) The structures of isomers of Pentane are:
(i)

Common name: n-pentane
IUPAC name:- Pentane
(ii)

Common name:- iso pentane
IUPAC name:- 2-methyl butane
(iii)

Common name- neo pentane
IUPAC name:- 2,2-dimethyl propane

Que-5: Write the

(a) Molecular formula
(b) Electron dot formula and
(c) Structural formula of methane and ethane

Ans: For methane:
(a) Molecular formula is CH₄
(b) Electron dot formula

(c) Structural formula

For ethane:
(a) Molecular formula is :- C₂H₆
(b) Electron dot formula:

(a) Structural Formula:

Que-6: How is

(a) Methane and
(b) Ethane prepared in the laboratory

Ans: 
(a) Laboratory preparation of methane:
When the mixture of sodium ethanoate and soda lime is taken in a hard glass test tube and heated, the gas evolved is methane. It is collected by downward displacement of water.
CH₃COONa+NaOH  →    Na₂CO₃+CH₄
(b) Laboratory preparation of ethane:
When the mixture of sodium propionate and soda lime is taken in the boiling tube and heated the ethane gas is evolved. It is also collected by downward displacement of water.
C₂H₅COONa+Na  →  OH   Na₂CO₃+C₂H₆

Que-7: How are methane and ethane prepared from methyl iodide and ethyl bromide?

Ans: When methyl iodide is reduced by nascent hydrogen at ordinary room temperature then methane is formed.
CH₃I+2[H]  →    CH₄+HI
When bromoethane is reduced by nascent hydrogen at ordinary room temperature then ethane is produced.
C₂H₅Br+2[H]    → C₂H₆+HBr

Que-8: What is substitution reaction? Give the reaction of chlorine with ethane and name the product formed?

Ans: A reaction in which one atom of a molecule is replaced by another atom (or group of atoms)is called a substitution reaction.
When ethane reacts with chlorine
C₂H₆ +Cl₂  →    C₂H₅Cl + HCl
Chloroethane
C₂H₅Cl + Cl₂     →   C₂H₄Cl₂+HCl
Dichloroethane
C₂H₄Cl₂ +Cl₂        →    C₂H₃Cl₃+HCl
Trichloroethane
C₂H₃Cl₃ + Cl₂     →   C₂H₂Cl₄ + HCl
Tetrachloroethane
C₂H₂Cl₄ +Cl₂    →  C₂HCl₅ +HCl
Penta chloroethane
C₂HCl₅ +Cl₂ →   C₂Cl₆ + HCl
Hexachloroethane

Que-9: Name the compounds formed when methane burns in

(a) Sufficient air(b) insufficient air
Give a balanced equation

Ans: 
(a) Sufficient air: When methane burns in sufficient air, then carbon dioxide and water vapors are formed.
CH₄ + 2O₂     →   CO₂+2H₂O
(b) Insufficient air: When methane burns in insufficient air , then carbon monoxide and water is formed.
2CH₄ + 3O₂ →  2CO + 4H₂O

Que-10: Write the names and formula of the products formed when

(a) Methane and (b) ethane , reacts with :
(i) Chlorine (ii) bromine
Write the chemical equations.

Ans: 
(a)(i) When methane reacts with chlorine in the presence of sunlight or UV light, it undergoes substitution reaction to form Tetrachloromethane.

(ii) When it reacts with bromine it forms Tetra bromomethane
CH₄ + Br₂     →   CH₃Br + HCl
CH₃Br + Br₂    →   CH₂Br₂ + HCl
Dibromo methane
CH₂Br₂ + Br₂      →   CHBr₃ + HCl
Tribromo methane
CHBr₃ + Br₂  →   CBr₄ + HCl
Tetra bromomethane
(b)
(i) When ethane reacts with chlorine it forms hexa choroethane.
C₂H₆ +Cl₂    → C₂H₅Cl + HCl
Chloroethane
C₂H₅Cl + Cl₂       →  C₂H₄Cl₂+HCl
Dichloroethane
C₂H₄Cl₂ +Cl₂  → C₂H₃Cl₃+HCl
Trichloroethane
C₂H₃Cl₃ + Cl₂  →    C₂H₂Cl₄ + HCl
Tetrachloroethane
C₂H₂Cl₄ +Cl₂  →    C₂HCl₅ +HCl
Penta chloroethane
C₂HCl₅ +Cl₂     →  C₂Cl₆ + HCl
Hexachloroethane
(ii) When ethane reacts with bromine it forms Hexa bromoethane
C₂H₆ +Br₂    →   C₂H₅Br + HBr
Bromoethane
C₂H₅B_r + Br₂  → C₂H₄Br₂+HBr
Dibromoethane
C₂H₄Br₂ +Br₂       →  C₂H₃Br₃+HBr
Tri bromoethane
C₂H₃Br₃ + Br₂     →    C₂H₂Br₄ + HBr
Tetra bromoethane
C₂H₂Br₄ +Br₂      →   C₂HBr₅ +HBr
Penta bromoethane
C₂HBr₅ +Br₂  →   C₂Br₆ + HBr
Hexa Bromoethane

Que-11: Name the compound prepared from

(a) Sodium propionate
(b) Methyl iodide
(c) Ethyl bromide
Write the balanced equation for the same

Ans: 
(a) Ethane is prepared from sodium propionate.
C₂H₅COONa+NaOH    →    Na₂CO₃+C₂H₆
(b) Methane is prepared from methyl iodide.
CH₃I+2[H] → CH₄+HI
(c) Ethane is prepared from ethyl bromide.
C₂H₅Br+2[H]  →    C₂H₆+HBr

Que-12: Write the equation for the complete combustion of (i) methane (ii) ethane.

Ans: 

Que-13: Convert

(a) Methane into chloroform
(b) Sodium acetate into methane
(c) Methyl iodide into ethane
(d) methane to methyl alcohol

Ans: 
(a) Methane into chloroform
CH₄+Cl₂   →  CH₃Cl+HCl
CH₃Cl+Cl₂ →  CH₂Cl₂+HCl
CH₂Cl₂+Cl₂ →  CHCl₃+HCl
(b) Sodium acetate into methane
CH₃COONa+NaOH  →  Na₂CO₃+CH₄
(c) Methyl iodide into ethane
2CH₃I +2Na  → CH₃-CH₃+2NaI
(d) Methane to methyl alcohol
CH₄   →  CH₃(OH)

Que-14: Give three uses of: (a) Methane (b) ethane

Ans: 
(a) Methane: Three uses of methane are:
(i) Methane is a source of carbon monoxide and hydrogen
(ii) It is used in the preparation of ethyne, methanal, chloromethane, carbon tetrachloride.
(iii) It is employed as a domestic fuel.
(b) Ethane:
Three uses of ethane are:
(i) It is used in the preparation of ethene, ethanol, and ethanol.
(ii) It forms ethyl chloride, which is used to make tetraethyllead.
(iii) It is also a good fuel.

Que-15: Under what conditions does ethane get converted to:

(a) Ethyl alcohol
(b) Acetaldehyde
(c) Acetic acid

Ans: 
(a) When a mixture of ethane and oxygen is compressed to about 120atm pressure and passed over copper tubes at 475K, ethyl alcohol is formed.
2C₂H₆ +O₂    →  2C₂H₅OH
(b) When mixture of ethane and oxygen is passed through heated molybdenum oxide, the mixture is oxidized to Acetaldehyde.
C₂H₆ +O₂    →  CH₃CHO+H₂O
(c) Ethanol formed from ethane gets oxidized to acetic acid.
2C₂H₆ +O₂   2  →  C₂H₅OH
C₂H₅OH + O₂      →   CH₃COOH+H₂O

Que-16: Using appropriate catalysts, ethane can be oxidized to an alcohol, an aldehyde and an acid. Name the alcohol, aldehyde and acid formed when ethane is oxidized.

Ans: Ethane can be oxidized as follows:
When a mixture of ethane and oxygen in the ratio 9:1 by volume is compressed to about 120 atm pressure and passed over copper tubes at 475K, ethyl alcohol is formed.
2C₂H₆ + O₂  →   2C₂H₅OH
When a mixture of ethane and oxygen is passed through heated MoO, the mixture is oxidized to ethanal.
C₂H₆+ O₂  →   CH₃CHO + H₂O
When a manganese based catalyst is used 100^oC, ethane can be oxidized to ethanoic acid.
2C₂H₆ + 3O₂   →  2CH₃COOH + 2H₂O

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