Lesson 6C.2

6C.2 Electrophilic addition mechanisms and tests Quiz: Pearson Edexcel Chemistry, Unit 6

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 6C.2, Electrophilic addition mechanisms and tests: 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 an electrophile?

    • A species that donates an electron pair
    • A species that always carries a negative charge
    • A species with an unpaired electron
    • A species that accepts an electron pair

  2. Which bond fission occurs in the first step of the electrophilic addition of Br2 to ethene?

    • The C=C bond breaks homolytically to form two radicals that then react with the bromine molecule
    • The C-H bond breaks homolytically with ultraviolet light to give a hydrogen radical and a radical
    • The Br-Br bond is polarised and the pi electrons attack one bromine atom, breaking the Br-Br bond heterolytically
    • The C-C sigma bond breaks by heterolysis to give two carbocations that recombine with bromide

  3. In the mechanism of ethene with bromine, where should a curly arrow start?

    • From the carbon atom, pointing to the sigma bond, to show the breaking of the carbon skeleton
    • From the C=C pi bond or a lone pair, pointing to the electrophile
    • From a radical dot, pointing to the carbon atom, to show the formation of a new bond
    • From a hydrogen atom, pointing to a bromine atom, to show the transfer of a hydrogen to the halogen

  4. What is the intermediate formed in the electrophilic addition of Br2 to ethene?

    • A carbocation, CH2BrCH2+
    • A carbanion, CH2BrCH2-
    • An ester, CH2BrCOOCH3
    • A free radical, CH2BrCH2*

  5. Which observation is used as a qualitative test for an alkene?

    • Bromine water changes from orange to colourless
    • A precipitate forms with acidified silver nitrate
    • Bromine water turns green
    • The solution turns from colourless to pink

  6. Why does an alkane not decolourise bromine water in the dark?

    • Alkanes react with bromine only in the presence of water, which acts as a catalyst in the mixture
    • Bromine water is too concentrated to react with alkanes, so the mixture stays orange in colour
    • Alkanes have no C=C double bond, so there is no electron-rich pi bond to react with bromine
    • Alkanes are polar molecules that dissolve bromine without any chemical reaction taking place

  7. Propene reacts with hydrogen bromide. What is the major product?

    • 2-bromopropane
    • Bromoethane
    • 1,2-dibromopropane
    • 1-bromopropane

  8. Which carbocation is most stable?

    • Tertiary carbocation
    • Secondary carbocation with an alkene attached
    • Methyl carbocation with no alkyl groups
    • Primary carbocation

  9. Why is the secondary carbocation formed in preference to a primary one during addition of HBr to propene?

    • Secondary carbocations contain a radical, which is more stable
    • Alkyl groups stabilise the positive charge, so the secondary carbocation is more stable
    • Br- attacks the primary carbon in the first step
    • The primary carbocation is always more stable than the secondary carbocation

  10. What is the major product when 2-methylpropene reacts with hydrogen chloride?

    • 2-chloro-2-methylpropane
    • 2-chloropropane
    • 1,2-dichloro-2-methylpropane
    • 1-chloro-2-methylpropane

  11. In electrophilic addition of hydrogen halides, which species acts as the electrophile?

    • The water molecule, which provides the OH group that adds to the carbocation in the second step
    • The halide ion X-, which attacks the double bond as a nucleophile and forms the new carbon-halogen bond
    • The carbon atom of the alkene, which donates its electrons to the hydrogen atom in the first step
    • The hydrogen atom in H-X, which is polarised and accepts electrons from the C=C bond

  12. Which statement describes the first step of electrophilic addition of HCl to ethene?

    • The pi electrons attack the H atom of HCl, forming a carbocation and Cl-
    • The C-H bond in ethene breaks, releasing a hydrogen radical
    • The Cl atom attacks the C=C bond to form a carbanion
    • The H-Cl bond breaks homolytically to give radicals

  13. Which compound forms as the major product when but-2-ene reacts with HBr?

    • 2-methylpropyl bromide
    • 2-bromobutane
    • 1-bromobutane
    • 1,2-dibromobutane

  14. Which intermediate is formed when propene reacts with H+ in the first step of hydration?

    • A secondary carbocation, CH3CH+CH3
    • A carbanion, CH3CH-CH3
    • A primary carbocation, CH3CH2CH2+
    • A radical, CH3CH*CH3

  15. What is the expected colour change of acidified potassium manganate(VII) when reacted with an alkene?

    • Blue to pink
    • Colourless to green
    • Yellow to orange
    • Purple to colourless

  16. What is the correct name for the product of Br2 with but-1-ene?

    • 1,1-dibromobutane
    • 2,3-dibromobutane
    • 1,4-dibromobutane
    • 1,2-dibromobutane

  17. Why is the electrophile attack on the C=C bond described as electrophilic addition rather than substitution?

    • The electrophile replaces a hydrogen atom on the alkene so that a substituted product is formed
    • Two new atoms are added across the double bond and no atom is removed
    • The product is a salt and water is removed in a condensation step with a loss of a small molecule
    • Radicals form and recombine on the carbon chain to give a substituted product with a new bond

  18. Which factor determines the regioselectivity of addition to an unsymmetrical alkene?

    • The presence of UV light only
    • The colour of the alkene
    • The relative stability of the carbocation intermediates
    • The number of carbon atoms in the chain only

  19. What is the principal reason a tertiary carbocation is more stable than a primary carbocation?

    • Three alkyl groups donate electron density to the positive carbon, stabilising it
    • The tertiary carbon has more hydrogen atoms bonded to it
    • Tertiary carbocations are radicals and are stabilised by electron pairing
    • The carbocation has a negative charge that offsets the positive

  20. When acidified aqueous bromine reacts with propene, which product is most likely to form?

    • 1-bromopropan-2-ol
    • 1,2-dibromopropane as the only product
    • Propan-2-ol without any bromine
    • 2-bromopropane with no oxygen

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