Lesson 3.3.1.2

3.3.1.2 Reaction mechanisms Quiz: AQA Chemistry, Unit 3

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.3.1.2, Reaction mechanisms: 20 multiple choice questions for the AQA Chemistry (7405), Unit 3: Organic chemistry, written with Revision Ninja.

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The 20 questions

  1. In a free-radical mechanism, how is the unpaired electron of a radical represented?

    • A curly arrow with two heads
    • A plus sign
    • A single dot
    • A pair of dots

  2. Which arrow is used to show the formation of a covalent bond in a mechanism?

    • A straight double-headed arrow
    • A curly arrow starting from the atom that gains the bond
    • A curly arrow starting from a lone pair or another covalent bond
    • A dashed arrow from the product

  3. Which arrow is used to show the breaking of a covalent bond in a mechanism?

    • A dotted line from the product
    • A curly arrow starting from the atom only
    • A curly arrow starting from the bond
    • A straight arrow ending at the bond

  4. In the free-radical chlorination of methane, what is the first step (initiation)?

    • Cl2 -> 2Cl radicals, under UV light
    • CH4 + Cl radical -> CH3 radical + HCl
    • Cl radical + Cl radical -> Cl2
    • CH3 radical + Cl2 -> CH3Cl + Cl radical

  5. Which step is a propagation step in the free-radical substitution of methane with chlorine?

    • Cl radical + Cl radical -> Cl2
    • CH4 + Cl radical -> CH3 radical + HCl
    • Cl2 -> 2Cl radicals
    • CH3 radical + CH3 radical -> C2H6 only

  6. Which of these is a termination step in a free-radical mechanism?

    • A molecule is ionised to form a cation
    • A radical is formed from Cl2 by UV light
    • Two radicals combine to form a stable molecule
    • A radical reacts with a molecule to make another radical

  7. Which equation represents a nucleophile attacking a carbon atom with curly arrows drawn correctly?

    • The carbon forms a lone pair and attacks the nucleophile
    • A lone pair on the nucleophile forms a bond to the carbon, while a bond to the leaving group breaks
    • A bond on the carbon forms a bond to the nucleophile with a lone pair
    • The leaving group forms a lone pair and attacks the carbon

  8. What is the role of an electrophile in an addition mechanism of an alkene?

    • It accepts a pair of electrons from the C=C double bond
    • It donates a pair of electrons to the C=C double bond
    • It removes a radical from the alkene
    • It breaks the C=C bond by homolytic fission only

  9. How many curly arrows are needed to show the formation of a carbocation from an alkene and H+ ?

    • One
    • Two
    • Three
    • None

  10. In the mechanism of the free-radical step CH3 radical + Cl2 -> CH3Cl + Cl radical, what is formed?

    • A methyl cation and a chloride ion
    • Two chlorine molecules only
    • A methyl chloride molecule and a new chlorine radical
    • Hydrogen chloride and methane

  11. Which species is a nucleophile in the reaction of OH- with bromoethane?

    • Bromoethane
    • CH3CH2+
    • OH-
    • Br-

  12. Which of these species is an electrophile?

    • H+
    • OH-
    • NH3
    • Br-

  13. Which of these is a radical?

    • Cl- with eight outer electrons
    • NH4+ with four bonds
    • CH3 with an unpaired electron
    • CH4 with four bonds

  14. Which statement about curly arrows in a mechanism is correct?

    • They are not used anywhere in organic mechanisms
    • They show the movement of single electrons only
    • They always start from an atom nucleus
    • They show the movement of an electron pair, not a single electron

  15. Which feature must be included when outlining an organic mechanism by drawing species and curly arrows?

    • A balanced equation with no structures
    • The structures of the species involved, with arrows showing electron pair movement
    • Only the names of the reactants and products
    • Only the molecular formula of the product

  16. In a free-radical mechanism, what is the role of ultraviolet light?

    • It removes the chlorine atom from the reaction
    • It makes the methane ionic
    • It stops the termination steps from occurring
    • It provides the energy to break the Cl-Cl bond homolytically

  17. Why do free-radical chain reactions produce several chlorinated products?

    • Radical substitution can continue on the products, so further chlorine atoms are substituted
    • The reaction only forms ionic compounds
    • The radicals are always stable and do not react further
    • The mechanism involves no radicals at all

  18. Explain why a termination step removes radicals from the chain.

    • A radical is converted to an ion that can continue the chain
    • Two radicals combine to form a stable molecule with no unpaired electrons
    • A radical splits into two new radicals
    • A radical is absorbed as a solid precipitate

  19. Write the correct arrow pattern for the heterolytic breaking of the C-Br bond in bromoethane to form an ion.

    • A straight arrow from the bromine to the hydrogen
    • A dashed arrow from the carbon to the methyl group
    • A curly arrow from the C-Br bond toward the bromine atom
    • A curly arrow from the carbon atom toward the hydrogen

  20. In the mechanism of the reaction of an alkene with H-Br, which species is formed as the intermediate?

    • A carbanion
    • A carbocation
    • A neutral alkane
    • A free radical only

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