3.3.10.1 Bonding Quiz: AQA Chemistry, Unit 3

The 20 questions

1. What is the length of the C-C bonds in benzene compared with single and double bonds?

   • The same as a double C=C bond, because benzene has three full double bonds
   • Longer than a single C-C bond, because the ring is strained by the planar geometry
   • Intermediate between single and double bond lengths
   • The same as a single C-C bond, because the delocalised electrons are localised

2. Which orbitals overlap to delocalise electrons in the benzene ring?

   • The d orbitals on each carbon atom, which overlap sideways to form the pi system
   • The sp3 orbitals pointing out of the ring, which overlap to form delocalised electrons
   • The p orbitals above and below the plane of the ring
   • The s orbitals along the C-C bonds, which overlap end to end to form the ring

3. Approximately what is the enthalpy of hydrogenation of cyclohexene?

   • -150 kJ mol-1
   • -120 kJ mol-1
   • -360 kJ mol-1
   • -208 kJ mol-1

4. The theoretical enthalpy of hydrogenation of cyclohexa-1,3,5-triene is -360 kJ mol-1, and the measured value for benzene is -208 kJ mol-1. What is the extra stability of benzene?

   • 152 kJ mol-1
   • 88 kJ mol-1
   • 360 kJ mol-1
   • 208 kJ mol-1

5. Why do substitution reactions occur in preference to addition reactions for benzene?

   • Benzene has no double bonds that can react with reagents in any conditions at all
   • Addition is always endothermic for aromatic compounds, so it never happens readily
   • Addition needs a catalyst that benzene cannot accept, so it cannot take place at all
   • Addition would destroy the delocalised pi system and its extra stability

6. What is the bond angle within the benzene ring?

   • 90 degrees
   • 109.5 degrees
   • 180 degrees
   • 120 degrees

7. Why is benzene more stable than the hypothetical cyclohexa-1,3,5-triene?

   • Cyclohexa-1,3,5-triene contains no double bonds at all, so it cannot be hydrogenated
   • Delocalisation of the p electrons lowers the energy of the molecule
   • Benzene contains more hydrogen atoms per molecule than the triene, lowering its energy
   • Benzene has longer C-C bonds than a triene, which makes the ring more stable overall

8. If each isolated C=C bond releases about 120 kJ mol-1 on hydrogenation, what is the predicted total for three C=C bonds?

   • -208 kJ mol-1
   • -120 kJ mol-1
   • -152 kJ mol-1
   • -360 kJ mol-1

9. What is the hybridisation of each carbon atom in the benzene ring?

   • sp2
   • sp3d
   • sp3
   • sp

10. Why is the C-C bond length in benzene intermediate between single and double bonds?

    • The delocalised electrons are spread over all six C-C bonds, giving bonds of equal intermediate character
    • Benzene has alternating single and double bonds of different lengths, which is why it reacts
    • The carbon atoms are held together by ionic attraction between positive and negative ring atoms
    • The ring contains only single bonds that are shortened by the high pressure of the air

11. Why does benzene decolourise bromine water far more slowly than cyclohexene?

    • Cyclohexene contains a triple bond that is easily broken by the bromine in the water
    • Benzene contains no carbon atoms in its ring, so bromine has nothing to attack
    • Bromine cannot dissolve in benzene at all, so no reaction with it can ever take place
    • The delocalised pi system is stable and is not readily attacked by bromine in an addition reaction

12. How many delocalised pi electrons are present in benzene?

    • 4
    • 2
    • 8
    • 6

13. Which statement about the p electrons in benzene is correct?

    • Each carbon contributes one p electron to a single delocalised system
    • Each carbon contributes two p electrons to separate C=C bonds
    • The p electrons are removed from the ring during reaction
    • The p electrons are localised between two carbon atoms only

14. Why is the hypothetical cyclohexa-1,3,5-triene used as a reference in benzene thermochemistry?

    • It represents benzene with three localised double bonds, so the difference shows the extra stability
    • It is the most stable isomer of C6H6 known to chemists, which is why it is used
    • It contains a carbon-carbon triple bond, which is why it is more reactive than benzene
    • It is the real product of benzene hydrogenation that is formed in the laboratory

15. Which of the following describes delocalisation correctly?

    • Electrons are fixed between two specific atoms in a single bond that does not move
    • Electrons move to the centre of the molecule and stop there, so no bonding is shared
    • Electrons are spread over more than two atoms in a region of overlapping orbitals
    • Electrons are removed from the molecule completely, leaving a positively charged ring

16. What is the approximate C-C bond length in benzene?

    • 0.120 nm
    • 0.154 nm
    • 0.139 nm
    • 0.134 nm

17. Which bonds are present in the benzene ring?

    • Only sigma bonds with no pi system at all
    • Three C=C double bonds that do not interact with each other
    • Alternating C-C single and C=C double bonds only
    • Sigma C-C and C-H bonds plus a delocalised pi system

18. Compared with cyclohexene, benzene is what in terms of electrophilic addition?

    • Much less reactive
    • Reactive only with radicals
    • Much more reactive
    • Equally reactive

19. What is the molecular shape of benzene?

    • A tetrahedral cage of carbon atoms
    • A non-planar chair with alternating carbons
    • A linear chain of six carbon atoms
    • A planar hexagonal ring

20. Which statement about the Kekule-type structure of benzene is correct?

    • It has only sigma bonds and no double bonds, which is why benzene is so unreactive
    • It shows localised double bonds that do not match the equal bond lengths found experimentally
    • It has a C-C triple bond that explains the short bonds found in the ring of benzene
    • It is the correct experimental structure with equal bond lengths found by diffraction

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