IBChemistryHLTopic QuestionsWhat are the Mechanisms of Chemical Change?Electron Sharing Reactions

Syllabus Edition

First teaching 2023

First exams 2025

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Electron Sharing Reactions (HL IB Chemistry)

Topic Questions

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11 mark

Which of these organic compounds would undergo free radical substitution?

 

I

 ethane

II

 fluoroethane

III

 ethene

IV

 ethanal

  • I only

  • I and II

  • I, II and III

  • All

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21 mark

Which equation represents a correct propagation step in the free radical substitution reaction between ethane and chlorine?

  • C2H6 + Cl • → C2H5Cl + H•

  • C2H5• + Cl2  → C2H5Cl + Cl • 

  • C2H6 + H• → C2H5• + HCl

  • C2H5• + Cl • → C2H5Cl 

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31 mark

Ultraviolet light initiates the following reaction.

alkane + chlorine → chloroalkane + hydrogen chloride

What happens to chlorine in this photochemical reaction?

  • heterolytic fission to give an electrophile

  • homolytic fission to give an electrophile

  • heterolytic fission to give a positive and negative ion

  • homolytic fission to give free radicals

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11 mark

Ethane reacts with bromine in the presence of ultraviolet light to form dibromoethane and hydrogen bromide.

The reaction proceeds via free radical substitution involving initiation, propagation and termination steps.

What is the minimum number of free radical mechanism steps to produce dibromoethane?

  • 5

  • 6

  • 7

  • 8

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21 mark

Ethane reacts with chlorine in the presence of ultraviolet light to form trichloroethane and hydrogen chloride.

The reaction proceeds via free radical substitution involving initiation, propagation and termination steps.

Which propagation equation is involved in the free radical reaction to form trichloroethane?

  • C2H6 + Cl● → C2H6● + HCl 

  • C2H3Cl2 + Cl● → C2H3Cl3 + H●

  • C2H5 + Cl2 → C2H5Cl  + Cl●

  • C2H4Cl● + Cl2 → C2H4Cl2 + Cl●

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31 mark

Ethane reacts with bromine in the presence of ultraviolet light to form tribromoethane and hydrogen bromide.

The reaction proceeds via free radical substitution involving initiation, propagation and termination steps.

Which equation represents a possible termination step in this reaction?

  • 2C2H4●  → C4H8

  • C2H4Br● + C2H5● → C4H9Br

  • C2H4● + C2H3Br● → C4H7Br

  • C2H3Br2● + C2H3Br● → C4H6Br3

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11 mark

In the presence of ultraviolet light, ethane and chlorine react to give a mixture of products.

Which compound could be present in the mixture of products?

  • CH3Cl

  • CH3CH2CH2Cl

  • CH3CH2CH2CH3

  • CH3CH2CH2CH2CH3

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21 mark

Which statements about the chlorine free radical are correct?

  1. It has 17 electrons.
  2. It is an uncharged species.
  3. It is formed by homolytic fission.

  • I and II only

  • I and III only

  • II and III only

  • I, II and III

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31 mark

Which organic product does not form in the following reaction?

C2H6 + Cl2 rightwards arrow with UV on top

  • C2H4Cl2 

  • C2H5Cl

  • C4H10 

  • Cl2 

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