Alkenes Organic Chemistry Class-10 Concise Exe-12C ICSE Chemistry Selina Solutions Chapter-12. We Provide Step by Step Answer of Exe-12(C) 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.

Alkenes Organic Chemistry Class-10 Concise Exe-12C ICSE Chemistry Selina Solutions Chapter-12

Board	ICSE
Book / Publication	Concise / Selina
Subject	Chemistry
Class	10th
Writer	Dr SP Singh
Chapter-12	Organic Chemistry
Exe-12C	Alkenes
Edition	2025-2026

Questions on Alkenes Hydrocarbon with Answers

Page-213

Que-1: Write : (a) molecular formula , (b) electron dot formula and (c) structural formula of ethene .(Ethylene)

Ans: 
(a) The molecular formula of ethene is C₂H₄
(b) Electron dot formula of ethene is:

(c) Structural formula of ethene:

Que-2: The molecules of alkene family are represented by a general formula C_nH_2n.Answer The following :

(a) What do n and 2n signify?
(b) What is the name of alkene when n=4?
(c) What is the molecular formula of alkene when n=4?
(d) What is the molecular formula of the alkene if there are ten H atoms in it?
(e) What is the structural formula of the third member of the alkene family?
(f) Write the molecular formula of lower and higher homologus of an alkene which contains four carbon atoms.

Ans: 
(a) n signifies the number of carbon atoms and 2n signifies the number of hydrogen atoms.
(b) The name of alkene when n=4 is Butene.
(c) The molecular formula of alkene when n=4 is C₄H_8.
(d) The molecular formula of alkene when there are 10 H atom in it C₅H_10.
(e) The structural formula of the third member of alkene is

(f) Lower homologus of alkene which contain four carbons is C₃H_6.
Higher homologus of alkene which contain four carbons is C₅H₁₀.

Que-3: 

(a)  Distinguish between the saturated hydrocarbon ethane and the unsaturated hydrocarbon ethene by drawing their structural formulae.
(b) Draw the structure of isomers of butane and write their IUPAC names.

Ans: 

Ethane	Ethene
It has carbon -carbon single bond.	It has carbon-carbon double bond
It is saturated.	It is unsaturated
Alkanes undergo substitution reaction.	Alkenes undergo addition reaction.

(b) There are two isomers are possible for butane:

Que-4: Give a balanced equation for the lab Preparation of ethylene. How is the gas collected?

Ans: 
Balanced Equation of ethylene:
CH₃-CH₂OH + H₂SO₄  →   CH₃-CH₂HSO₄+H₂O
CH₃-CH₂HSO₄    →   CH₂=CH₂
The gas is collected by downward displacement of water.

Que-5: How is ethene prepared by:

(a) De hydro halogenation reaction?
(b) Dehydration reaction?
Give equations and name the products formed.

Ans: 
(a) Dehydrohalogenation reaction:
C₂H₅Cl + KOH(alc.and hot)  →   C₂H₄ + KCl + H₂O
Ethene
(b) Dehydration reaction:
C₂H₅OH    → (Al₂O₃)  C₂H₄+H₂O
Ethene

Que-6: 

(a) Ethylene when reacts with halogens (chlorine and bromine) form saturated products. Name them and write balanced equations.
(b) Give the conditions and the main product formed by hydrogenation of ethylene.

Ans: 
(a) Chlorine and bromine are added to the double bond of ethene to form saturated ethylene chloride and ethylene bromide respectively.
CH₂ = CH₂ + Cl₂       →  CH₂(Cl)-CH₂(Cl)
1,2-dichloro ethane
CH₂ = CH₂ + Br₂    →   CH₂(Br)-CH₂(Br)
1,2-dibromo ethane
(b)  When ethene and hydrogen are passed over finely divided catalyst such as platinum or palladium at ordinary temperature or nickel at 200^o C, the two atom of hydrogen molecule are added to the unsaturated molecule, which thus becomes a saturated one.
C₂H₄ +H₂    →  (Ni) (200º)   C₂H₆

Que-7: Convert ethanol into ethene using

(a) Solid dehydrating agent
(b) Hot conc. H₂SO₄
Give only balanced equations.

Ans: 
Conversion of ethanol to ethene by using
(a) Solid dehydrating agent:
C₂​H₅OH  → (Al2​O3)(350º) C₂​H₄ + H₂​O
(b) Hot conc. H₂SO₄:
C₂​H₅OH + H₂SO₄   →  C₂​H4 + H₂O

Que-8: Write the following properties of ethene:

(a) Physical state
(b) Odour
(c) Density as compared to air
(d) Solubility

Ans: 
(a) Physical state: Ethene is a colourless and inflammable gas.
(b) Odour: It has faint sweetish odour.
(c) Density as compared to air: It has density less than one hence it is lighter than air.
(d) Solubility: It is sparingly soluble in water but highly soluble in organic solvents like alcohol, ether and chloroform.

Que-9: How would you convert:

(a) ethyl bromide into ethene
(b) Ethene into 1,2-dibromoethane
(b) Ethene into ethane

Ans: 
(a) Ethene into ethyl bromide: When ethene is treated with HBr bromoethane is formed.
CH₂=CH₂ + HBr → CH₃-CH₂Br
Ethyl bromide
(b) Ethene into 1, 2 -dibromoethane: Ethene reacts with bromine at room temperature to form saturated ethylene chloride.
CH₂=CH₂ + Br₂  →    CH₂(Br)-CH₂(Br)
1,2-dibromo ethane
(c) C₂H₄ + H₂ →    C₂H₆

Que-10: Give balanced equation when:

(a) Ethene is burnt in excess of oxygen
(b) Ethene reacts with chlorine (2019)
(c) Ethene combines with Hydrogen chloride
(d) A mixture of ethene and hydrogen is passed over nickel at 200⁰C.

Ans: 
(a) C₂H₄+3O₂     →  2CO₂ +2H₂O + heat
(b) CH₂=CH₂+Cl₂            →    CH₂(Cl)-CH₂(Cl)
(c) CH₂=CH₂ + HCl      →   CH₃-CH₂-Cl
(d) C₂H₄ +H₂     → (Ni)  C₂H₆

Que-11: Give the formula and names of A, B ,C and D in the following equations:

Ans: 

A= mono chloromethane
B= di chloromethane
C=Tri chloromethane
D=Tetra chloromethane

A= Ethene
B=ethane
C=bromoethane
D=dibromoethane
(c) C₂H₄ +H₂     →   C₂H₆
B= hydrogen

Que-12: Write the name and formula of the product formed in each case below:

(a) C₂H₄ +Cl_{2    →}   ______
(b) C₂H₅Br +KOH (alc.)  →      ______
(c) CH₂=CH₂    →   _______
(d) CH₂=CH₂+HBr    →  _______

Ans: 
(a) C₂H₄ +Cl₂     →  CH₂(Cl)-CH₂(Cl)
1,2- dichloro ethan
(b) C₂H₅Br +KOH (alc.)   →  C₂H₄ +KBr +H₂O
Ethane
(c) CH₂=CH₂  →  CH₂(OH)-CH₂(OH)
1,2- Ethandio
(d) CH₂=CH₂+HBr  → CH₃-CH₂Cl
chloroethane

Que-13: What do you observe when ethylene is passed through alkaline KMnO₄ solution?

Ans: 
When ethylene is passed through alkaline KMnO₄ solution 1, 2-Ethanediol is formed. The Purple color of KMnO₄ decolorizes.
CH₂=CH₂+H-O-H +[O]    →  CH₂(OH)-CH₂(OH)
Cold alkaline
KMnO₄ solution

Que-14: Name three compounds formed by ethylene and give the use of these compounds.

Ans: Three compounds formed by ethylene are: Polythene, Ethano , Epoxyethane
Uses of above compounds: Polythene is used as carry bags. Ethanol is used as a starting material for other products, mainly cosmetics and toiletry preparation. Epoxyethane is used in the manufacture of detergents.

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