Lesson 6B.2

6B.2 Radical substitution of alkanes Quiz: Pearson Edexcel Chemistry, Unit 6

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 6B.2, Radical substitution of alkanes: 20 multiple choice questions for the Pearson Edexcel Chemistry (9CH0), Unit 6: Organic Chemistry I, written with Revision Ninja.

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The 20 questions

  1. What is a radical, as used in reaction mechanisms?

    • A species with a complete octet and a net positive charge
    • A species formed by heterolytic fission with a lone pair
    • A species with an unpaired electron, shown by a single dot
    • A species with two unpaired electrons in a double bond

  2. Which process produces radicals from a covalent bond?

    • Homolytic fission, where each atom takes one electron from the shared pair
    • Electrophilic addition, where a pi bond is attacked
    • Heterolytic fission, where one atom takes both electrons from the shared pair
    • Nucleophilic substitution, where a lone pair attacks carbon

  3. Which equation shows the initiation step in the chlorination of methane in the presence of UV light?

    • Cl2 -> 2Cl*
    • Cl* + Cl* -> Cl2
    • CH4 + Cl* -> CH3* + HCl
    • CH3* + Cl2 -> CH3Cl + Cl*

  4. Which is a propagation step in the chlorination of methane?

    • Cl* + CH4 -> CH3* + HCl
    • CH3Cl + Cl* -> CH2Cl2 + HCl*
    • CH3* + CH3* -> C2H6
    • Cl2 -> 2Cl*

  5. Which equation represents a termination step in the radical substitution of methane?

    • CH3* + CH3* -> C2H6
    • Cl2 -> 2Cl*
    • Cl* + CH4 -> CH3* + HCl
    • CH4 + Cl2 -> CH3Cl + HCl

  6. Why is ultraviolet light needed for the reaction between methane and chlorine?

    • It stops the termination steps from happening by removing radicals from the mixture before they combine
    • It supplies energy to break the Cl-Cl bond homolytically in the initiation step
    • It acts as a catalyst that is regenerated in every propagation step and so is never used up
    • It converts methane into a methyl radical directly before any chlorine molecules are involved in the process

  7. Which chloromethane is formed first in the radical substitution of methane when chlorine is in excess?

    • CHCl3, trichloromethane
    • CH3Cl, chloromethane
    • CCl4, tetrachloromethane
    • CH2Cl2, dichloromethane

  8. Why is radical substitution of alkanes a poor method for making a single pure product?

    • Chlorine cannot react with alkanes at any temperature
    • The reaction only forms carbon dioxide and water
    • The radicals always react with the solvent instead of the alkane
    • Further substitution occurs, giving a mixture of chlorinated products

  9. How many different chlorinated products can be formed from the radical chlorination of methane?

    • 5
    • 4
    • 2
    • 3

  10. Which description correctly defines a propagation step?

    • A molecule gains an electron from a metal surface and becomes a negatively charged ion
    • A radical reacts with a molecule to form a new radical, so the chain continues
    • A molecule splits into two radicals when it absorbs ultraviolet light in the reaction vessel
    • Two radicals combine to form a stable molecule and so the chain is terminated at that point

  11. What is the major organic product of the reaction between ethane and chlorine in UV light, assuming monosubstitution?

    • Chloroethane, CH3CH2Cl
    • Tetrachloroethane, CHCl2CHCl2
    • Ethene, CH2=CH2
    • Dichloroethane, CH2ClCH2Cl

  12. Which species is the methyl radical?

    • CH4*
    • CH3-
    • CH3*
    • CH3+

  13. In the radical chain mechanism, which step is most likely to give ethane as a by-product?

    • Propagation by chlorine radical attacking methane
    • Termination by two methyl radicals combining
    • Hydrolysis by water attacking the methyl radical
    • Initiation by homolysis of chlorine

  14. Which statement correctly describes homolytic fission compared with heterolytic fission?

    • Heterolytic fission is only possible in the presence of UV light
    • Homolytic fission gives ions, whereas heterolytic fission gives radicals
    • Both produce only neutral molecules
    • Homolytic fission gives radicals, whereas heterolytic fission gives ions

  15. What is the overall equation for the monochlorination of methane?

    • CH4 + HCl -> CH3Cl + H2
    • CH4 + 2Cl2 -> CCl4 + 2H2
    • CH4 + Cl2 -> CH2Cl2 + H2
    • CH4 + Cl2 -> CH3Cl + HCl

  16. Why is the chlorination of ethane classified as a substitution reaction?

    • A small molecule is removed to form a double bond
    • Two atoms are added across a double bond
    • A carbon-carbon bond is broken by oxidation
    • A hydrogen atom is replaced by a chlorine atom

  17. Which species is produced in the propagation step between a chlorine radical and methane?

    • A carbene, CH2
    • A chloride ion, Cl-
    • A methyl radical, CH3*
    • A methylium ion, CH3+

  18. What is the systematic IUPAC name of CHCl3?

    • Chloromethane
    • Trichloromethane
    • Dichloromethane
    • Tetrachloromethane

  19. Which species is the chain carrier in the radical substitution of an alkane?

    • A nucleophile such as OH-
    • A radical, such as Cl* or CH3*
    • A catalyst that remains unchanged
    • A carbocation such as CH3+

  20. Which description best matches a termination step in radical substitution?

    • Two radicals combine so that no further radicals are formed
    • A proton is transferred to the product
    • A chlorine atom is removed from the product
    • A radical splits a covalent bond to form a new radical

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