NCERT Solutions for Class 11 Chemistry Chemistry Part-2 Chapter 13

Hydrocarbons Class 11

Chapter 13 Hydrocarbons Exercise Solutions

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Exercise : Solutions of Questions on Page Number : 396

Q1 :  

How do you account for the formation of ethane during chlorination of methane?


Answer :

Chlorination of methane proceeds via a free radical chain mechanism. The whole reaction takes place in the given three steps.

Step 1: Initiation:

The reaction begins with the homolytic cleavage of Cl – Cl bond as:

Step 2: Propagation:

In the second step, chlorine free radicals attack methane molecules and break down the C–H bond to generate methyl radicals as:

These methyl radicals react with other chlorine free radicals to form methyl chloride along with the liberation of a chlorine free radical.

Hence, methyl free radicals and chlorine free radicals set up a chain reaction. While HCl and CH3Cl are the major products formed, other higher halogenated compounds are also formed as:

Step 3: Termination:

Formation of ethane is a result of the termination of chain reactions taking place as a result of the consumption of reactants as:

Hence, by this process, ethane is obtained as a by-product of chlorination of methane.

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Q2 :  

Write IUPAC names of the following compounds:

a.

b.

c.

d.

e.

f.

g.


Answer :

(a)

IUPAC name: 2-Methylbut-2-ene

(b)

IUPAC name: Pen-1-ene-3-yne

(c) can be written as:

IUPAC name: 1, 3-Butadiene or Buta-1,3-diene

(d)

IUPAC name: 4-Phenyl but-1-ene

(e)

IUPAC name: 2-Methyl phenol

(f)

IUPAC name: 5-(2-Methylpropyl)-decane

(g)

IUPAC name: 4-Ethyldeca-1, 5, 8-triene

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Q3 :  

For the following compounds, write structural formulas and IUPAC names for all possible isomers having the number of double or triple bond as indicated:

(a) C4H8 (one double bond)

(b) C5H8 (one triple bond)


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Q4 :  

Write IUPAC names of the products obtained by the ozonolysis of the following compounds:

(i) Pent-2-ene (ii) 3,4-Dimethyl-hept-3-ene

(iii) 2-Ethylbut-1-ene (iv) 1-Phenylbut-1-ene


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Q5 :  

An alkene 'A' on ozonolysis gives a mixture of ethanal and pentan-3-one. Write structure and IUPAC name of 'A'.


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Q6 :  

An alkene 'A' contains three C - C, eight C - H ÃÆ’ bonds and one C - C À bond. 'A' on ozonolysis gives two moles of an aldehyde of molar mass 44 u. Write IUPAC name of 'A'.


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Q7 :  

Propanal and pentan-3-one are the ozonolysis products of an alkene? What is the structural formula of the alkene?


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Q8 :  

Write chemical equations for combustion reaction of the following hydrocarbons:

(i) Butane  (ii) Pentene (iii) Hexyne (iv) Toluene


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Q9 :  

Draw the cis and trans structures of hex-2-ene. Which isomer will have higher b.p. and why?


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Q10 :  

Why is benzene extra ordinarily stable though it contains three doublebonds?


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Q11 :  

What are the necessary conditions for any system to be aromatic?


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Q12 :  

Explain why the following systems are not aromatic?

(i)

(ii)

(iii)


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Q13 :  

How will you convert benzene into

(i) p-nitrobromobenzene (ii) m-nitrochlorobenzene

(iii) p -nitrotoluene (iv) acetophenone


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Q14 :  

In the alkane H3C-CH2-C(CH3)2-CH2-CH(CH3)2, identify 1°,2°,3° carbon atoms and give the number of H atoms bonded to each one of these.


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Q15 :  

What effect does branching of an alkane chain has on its boiling point?


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Q16 :  

Addition of HBr to propene yields 2-bromopropane, while in the presence of benzoyl peroxide, the same reaction yields 1-bromopropane. Explain and give mechanism.


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Q17 :  

Write down the products of ozonolysis of 1, 2-dimethylbenzene (o-xylene). How does the result support Kekulé structure for benzene?


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Q18 :  

Arrange benzene, n-hexane and ethyne in decreasing order of acidic behaviour. Also give reason for this behaviour.


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Q19 :  

Why does benzene undergo electrophilic substitution reactions easily and nucleophilic substitutions with difficulty?


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Q20 :  

How would you convert the following compounds into benzene?

(i) Ethyne (ii) Ethene (iii) Hexane


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Q21 :  

Write structures of all the alkenes which on hydrogenation give 2-methylbutane.


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Q22 :  

Arrange the following set of compounds in order of their decreasing relative reactivity with an electrophile, E+

(a) Chlorobenzene, 2,4-dinitrochlorobenzene, p-nitrochlorobenzene

(b) Toluene, p-H3C-C6H4-NO2, p-O2N-C6H4-NO2.


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Q23 :  

Out of benzene, m-dinitrobenzene and toluene which will undergo nitration most easily and why?


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Q24 :  

Suggest the name of a Lewis acid other than anhydrous aluminium chloride which can be used during ethylation of benzene.


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Q25 :  

Why is Wurtz reaction not preferred for the preparation of alkanes containing odd number of carbon atoms? Illustrate your answer by taking one example.


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Chemistry Part-2 - Chemistry : CBSE NCERT Exercise Solutions for Class 11th for Hydrocarbons will be available online in PDF book form soon. The solutions are absolutely Free. Soon you will be able to download the solutions.

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