Lesson 3.3.7

3.3.7 Optical isomerism Quiz: AQA Chemistry, Unit 3

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.3.7, Optical isomerism: 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. Which property differs between two optical isomers?

    • Their molar mass, which is the same for both enantiomers of a chiral compound
    • Their effect on plane-polarised light
    • Their molecular formula, which is identical for both enantiomers in every case
    • Their number of carbon atoms, which is identical for both enantiomers of a molecule

  2. What structural feature is required for optical isomerism in a simple molecule?

    • A benzene ring in the molecule that gives the structure a planar, rigid geometry
    • Two identical functional groups on one carbon atom that cancel the chirality
    • An asymmetric carbon atom bonded to four different groups
    • A double bond between two carbon atoms that makes the molecule planar and rigid

  3. What is the term for a pair of non-superimposable mirror images?

    • Structural isomers
    • Enantiomers
    • Diastereomers
    • Conformers

  4. What is a racemic mixture?

    • A mixture of two molecules with different formulae
    • An equal mixture of two enantiomers
    • A mixture containing only one enantiomer
    • A mixture of two different functional groups

  5. Why is a racemic mixture optically inactive?

    • Neither enantiomer can interact with plane-polarised light at any wavelength
    • The rotations of the two enantiomers are equal and opposite, so they cancel
    • The enantiomers form a polymer that scatters the light and removes all rotation
    • The mixture contains no carbon atoms, so it cannot be optically active at all

  6. How many chiral centres does 2-chlorobutane contain?

    • 1
    • 2
    • 3
    • 0

  7. Which compound is chiral?

    • 2-bromobutane
    • 2-bromopropane
    • 2-methylpropan-2-ol
    • Propan-2-ol

  8. How many stereoisomers does lactic acid, CH3CH(OH)COOH, have?

    • 1
    • 2
    • 4
    • 3

  9. A molecule has exactly one chiral centre. How many optical isomers does it have?

    • 1
    • 3
    • 4
    • 2

  10. Which pair of structures are enantiomers?

    • Two molecules with different molecular formulae
    • A molecule and its non-superimposable mirror image
    • Two molecules with the same structure rotated in space
    • Two molecules that differ in the position of a double bond

  11. What is a chiral centre?

    • A carbon atom bonded to two identical groups
    • A carbon atom bonded to four different groups
    • A carbon atom in a C=C double bond
    • A carbon atom in a benzene ring

  12. Passing plane-polarised light through a solution of sucrose is used to show what?

    • The melting point of sucrose
    • The pH of a sugar solution
    • Optical activity of the sugar
    • The concentration of sucrose only

  13. In a 3D displayed formula of a chiral carbon, what does a solid wedge bond represent?

    • A bond lying behind the plane of the paper
    • A bond coming out of the plane towards the viewer
    • A double bond within the plane of the paper
    • A bond to a hydrogen atom only

  14. Why do enantiomers have identical melting points and identical infrared spectra?

    • They contain different numbers of carbon atoms, so their boiling points differ
    • They have the same bonds and functional groups and differ only in 3D arrangement
    • They have identical optical rotations, so the polarimeter cannot tell them apart
    • They always form the same racemic mixture when left standing in solution

  15. Which alcohol is chiral?

    • 2,2-dimethylpropan-1-ol
    • Butan-1-ol
    • 2-methylpropan-1-ol
    • 2-methylbutan-1-ol

  16. A planar carbonyl carbon is attacked by a nucleophile. Why is a racemic mixture formed?

    • The nucleophile can attack from either face of the planar carbon with equal probability
    • The nucleophile is always a hydrogen atom that adds from one face only
    • The carbonyl oxygen is lost as a gas, so no product with a chiral centre forms
    • The carbonyl carbon is always chiral before the nucleophile attacks the molecule

  17. Which statement about enantiomers is INCORRECT?

    • They rotate plane-polarised light by the same amount in the same direction
    • They have identical melting points, because they share the same intermolecular forces
    • They rotate plane-polarised light by the same amount in the same direction each time
    • They have identical infrared spectra, because they contain the same bonds and groups

  18. Which compound has no chiral centre?

    • 2-chlorobutane
    • 2-bromobutane
    • Lactic acid
    • 2-bromopropane

  19. A sample of one enantiomer rotates plane-polarised light by +10 degrees. What rotation does its pure mirror-image enantiomer give?

    • -10 degrees
    • +20 degrees
    • 0 degrees
    • +10 degrees

  20. A mixture contains 75% of the (+) enantiomer and 25% of the (-) enantiomer, where each pure form rotates by 10 degrees. What is the observed net rotation?

    • +5 degrees
    • 0 degrees
    • +10 degrees
    • -5 degrees

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