Lesson 17A.1

17A.1 Chirality, optical isomers and racemic mixtures Quiz: Pearson Edexcel Chemistry, Unit 17

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 17A.1, Chirality, optical isomers and racemic mixtures: 20 multiple choice questions for the Pearson Edexcel Chemistry (9CH0), Unit 17: Organic Chemistry II, written with Revision Ninja.

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The 20 questions

  1. What structural feature must a molecule have to be chiral and show optical isomerism in the simplest case?

    • A single carbon atom bonded to four different groups
    • A carbon atom bonded to two identical hydrogen atoms and one oxygen atom
    • A benzene ring with two identical substituents in the 1,4 positions
    • A carbon-carbon double bond with two different groups on each carbon

  2. What are optical isomers?

    • Molecules with the same shape but different numbers of carbon atoms
    • Molecules that differ only in the position of a double bond
    • Molecules with the same structure but a different order of bonded atoms
    • Non-superimposable mirror images of each other

  3. What is optical activity?

    • The ability of a single optical isomer to rotate the plane of plane-polarised monochromatic light
    • The ability of a solution to conduct electricity through dissolved ions
    • The ability of a compound to absorb ultraviolet light at a specific wavelength
    • The ability of a molecule to emit light after being exposed to a laser

  4. What is a racemic mixture?

    • A mixture of two different structural isomers in equal amounts
    • A pure optical isomer that rotates light by 180 degrees
    • An equimolar mixture of two enantiomers, which is optically inactive
    • A mixture of a chiral compound with an achiral solvent in a 1:1 ratio

  5. A racemic mixture shows no net rotation of plane-polarised light. Why?

    • The two enantiomers rotate the light equally in opposite directions, so the effects cancel
    • The light is absorbed completely by the mixture before reaching the detector
    • Neither enantiomer is able to interact with plane-polarised light at all
    • The mixture contains no chiral centres, so there is no asymmetry to rotate light

  6. Which molecule contains a single chiral centre?

    • 2-bromopropane
    • 2-bromobutane
    • 2-methylpropan-2-ol
    • 1-bromobutane

  7. How many stereoisomers does a molecule with two chiral centres have, if it has no meso form?

    • 2
    • 3
    • 4
    • 8

  8. Lactic acid (2-hydroxypropanoic acid) has one chiral centre. How many optical isomers does it have?

    • 3
    • 1
    • 4
    • 2

  9. Which reaction is most likely to produce a racemic mixture?

    • Reduction of an achiral ketone by a hydride ion, which gives an achiral alcohol
    • Esterification of ethanoic acid with ethanol, which has no chiral centre
    • SN2 hydrolysis of a primary halogenoalkane, where inversion occurs at the carbon
    • SN1 hydrolysis of an optically active halogenoalkane, which proceeds via a planar carbocation

  10. Why is the product of SN2 hydrolysis of a chiral halogenoalkane optically active?

    • The product is a mixture of an alkene and an alcohol, and each component rotates polarised light by a different amount
    • The nucleophile attacks from the side opposite the leaving group, so the configuration is inverted and one enantiomer is favoured
    • The nucleophile attacks equally from both faces of the molecule, so a racemic mixture of two enantiomers is formed
    • The product has no chiral centre, so it rotates polarised light in both directions and cancels out to zero overall

  11. A compound rotates plane-polarised light by +10 degrees. Its enantiomer rotates it by which value under the same conditions?

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

  12. Which statement about the number of chiral centres in a molecule is correct?

    • A molecule with several chiral centres may still be achiral overall if it has an internal plane of symmetry
    • Every molecule that contains two or more carbon atoms in a chain must always have at least one chiral centre present
    • A molecule can only be chiral if it contains a benzene ring, because the ring is needed for asymmetry in the structure
    • Chiral centres cannot occur in any molecule that contains oxygen, because oxygen atoms always create symmetry in bonds

  13. In a molecule written as a 2D diagram, how is a chiral centre identified?

    • Any carbon atom bonded to an oxygen atom, since the oxygen atom makes the molecule asymmetric about that carbon
    • A carbon atom bonded to four different groups, shown with wedge or dash bonds where appropriate
    • A carbon atom bonded to a double bond and a hydrogen atom, which always creates a stereocentre in the molecule
    • A carbon atom that forms part of a benzene ring, since the delocalised electrons in the ring create asymmetry

  14. A reaction produces a product that is optically active from achiral reactants with no chiral catalyst. What does this suggest?

    • The product must be racemic, since achiral reactants cannot give a net optical rotation without a chiral influence
    • The product must have no chiral centres, since optical activity needs achiral starting materials
    • The product is definitely a single enantiomer, because achiral reactants always give pure optical isomers
    • The product must be an alkene, since alkenes are always optically active

  15. Why do optical isomers have identical melting temperatures and boiling temperatures?

    • They are constitutional isomers with the same molecular formula but different bonding order between their atoms
    • They always decompose into the same products before reaching a boiling point, so their boiling points cannot be measured
    • They have different molar masses because each enantiomer has a different orientation of its atoms in space
    • They have the same intermolecular forces, since mirror-image molecules have identical bonds and shape in every other respect

  16. What is the relationship between a racemic mixture and optical activity?

    • A racemic mixture rotates light by twice the angle of a single enantiomer
    • A racemic mixture is more optically active than either enantiomer alone
    • A racemic mixture is optically active only when heated above 100 C
    • A racemic mixture is optically inactive because the rotations of its two enantiomers cancel

  17. The rate of an SN1 hydrolysis of an optically active halogenoalkane is monitored by polarimetry. What is observed as the reaction goes to completion?

    • The optical rotation increases steadily, since more chiral product forms
    • The optical rotation falls to zero as a racemic mixture forms
    • The optical rotation stays constant, since the mass of chiral material is unchanged
    • The optical rotation changes sign, since the product is a single enantiomer

  18. Which statement describes a chiral molecule?

    • A molecule that has no carbon-hydrogen bonds
    • A molecule that contains only double bonds in its carbon chain
    • A molecule whose mirror image is identical to the original molecule
    • A molecule that cannot be superimposed on its mirror image

  19. A student measures the optical rotation of a solution of a racemic mixture. What result is expected?

    • A rotation that depends on the wavelength of the light only
    • A large positive rotation, since two enantiomers are present
    • Zero rotation, since the two enantiomers cancel each other
    • A large negative rotation, since the mixture is more concentrated

  20. Which molecule is achiral?

    • 2-methylpropan-2-ol
    • 2-chlorobutane
    • 2-hydroxypropanoic acid
    • 2-bromopentane

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