18A.3 Phenol and its bromination Quiz: Pearson Edexcel Chemistry, Unit 18

The 20 questions

1. Which reagent is used to brominate phenol at room temperature?

   • Bromine water
   • Liquid bromine with aluminium bromide, heated
   • Bromine in carbon tetrachloride with an iron catalyst
   • Hydrogen bromide gas in the dark

2. What is the product of phenol with bromine water?

   • 2,4-dibromophenol, with no precipitate
   • 1-bromophenol, which forms a colourless solution
   • Bromobenzene with HBr gas
   • 2,4,6-tribromophenol, which forms as a white precipitate

3. Why does phenol react with bromine water without a catalyst?

   • Phenol has a permanent positive charge on the ring that attracts the bromine molecule before any reaction
   • The oxygen lone pair donates electron density into the ring, making it more reactive towards electrophiles
   • The hydroxyl group removes electrons from the ring by induction, making it more reactive towards electrophiles
   • Bromine water is a catalyst that makes the bromine more reactive, so the reaction can proceed at room temperature

4. Which group in phenol makes the ring more reactive than benzene?

   • The -OH group, whose oxygen lone pair is donated into the ring
   • The ring itself, which has a permanent dipole with a negative end on carbon
   • Water molecules that hydrogen-bond to phenol in solution
   • The -CH3 group, which withdraws electron density from the ring

5. Calculate the relative molecular mass of 2,4,6-tribromophenol, C6H3Br3O, using Ar: C 12.0, H 1.0, Br 79.9, O 16.0.

   • 173.0
   • 252.9
   • 409.5
   • 330.7

6. How many moles of bromine react with one mole of phenol to give the tribromo product?

   • 6
   • 2
   • 1
   • 3

7. 0.10 mol of phenol gives 0.080 mol of 2,4,6-tribromophenol. What is the percentage yield?

   • 80%
   • 125%
   • 10%
   • 8%

8. Why is no catalyst needed for bromination of phenol but needed for benzene?

   • Benzene is aromatic so it cannot react at all with bromine, while phenol behaves as an alkene in the reaction
   • The ring of phenol is activated by the oxygen lone pair, so the weak electrophile in bromine water attacks it
   • Phenol reacts only with HBr, which forms the catalyst in situ, so no separate catalyst needs to be added
   • Phenol contains more bromine atoms per molecule than benzene does, so the reaction needs less catalyst overall

9. Which positions on the phenol ring are activated for electrophilic substitution?

   • Only the 1 position, where the -OH group is attached
   • The 2, 4 and 6 positions, which are ortho and para to the -OH group
   • Only the 3 and 5 positions, which are meta to the -OH group
   • The 1 and 3 positions, which are ortho and meta to the -OH group

10. Which equation for the tribromination of phenol is correct?

    • C6H5OH + 2Br2 -> C6H3Br2OH + 2HBr
    • C6H5OH + 3Br2 -> C6H2Br3OH + 3HBr
    • C6H5OH + Br2 -> C6H5OHBr2
    • C6H5OH + 4Br2 -> C6H2Br4OH + 4HBr

11. What is observed when bromine water is added to phenol?

    • The orange bromine water is decolourised and a white precipitate forms
    • The orange colour deepens and a clear yellow solution remains
    • The solution turns green and a brown solid forms
    • The solution turns purple and gas bubbles are produced

12. A student predicts that benzene and phenol react with bromine water at the same rate. Which evaluation is best?

    • The prediction is wrong because the -OH group activates the ring, so phenol brominates much faster without a catalyst
    • The prediction is right because both are aromatic, so the delocalised ring reacts with bromine at the same rate
    • The prediction is wrong because benzene is more reactive than phenol, since its six pi electrons are more available
    • The prediction is right because phenol is less polar than benzene, so both molecules react with bromine equally

13. Why is the reaction of phenol with bromine water substitution rather than addition?

    • Addition is slower than substitution in all aromatic compounds at room temperature
    • Bromine adds only to C-O bonds, which phenol does not contain
    • Phenol has no double bonds, so addition is impossible with any bromine species
    • Phenol is aromatic, so addition would destroy the delocalised ring, and substitution restores it

14. Using Mr = 330.7 for 2,4,6-tribromophenol, what mass forms from 0.100 mol of phenol at 100% yield?

    • 33.1 g
    • 94.0 g
    • 9.40 g
    • 18.8 g

15. Which statement describes the use of the 2,4,6-tribromophenol test?

    • A test for alkenes, since the bromine water is decolourised by addition
    • A test for carbonyl compounds, since a precipitate forms with bromine
    • A qualitative test to detect phenol, since a white precipitate forms rapidly
    • A test for amines, since the bromine water forms a salt with the amine

16. Which property of phenol makes it weakly acidic, enabling it to react with sodium hydroxide?

    • Phenol contains a carbonyl group that donates a proton to the hydroxide ion, forming a neutral salt
    • The -OH group is attached to a ring, and the phenoxide ion formed is stabilised by delocalisation of its charge
    • Phenol has a permanent negative charge that is neutralised by sodium ions, which is why it is weakly acidic
    • The -OH group is attached to a CH2 group, so the O-H bond breaks easily and the proton is released in water

17. Which species attacks the ring of phenol during bromination?

    • The hydroxide ion acting as a nucleophile that replaces the bromine atom on the ring
    • Br- acting as a nucleophile that attacks the electron-rich ring of phenol directly
    • Br+ or a polarised bromine species, acting as the electrophile
    • A carbanion formed on the oxygen atom, which then attacks the bromine molecule

18. How many hydrogen atoms are attached directly to the benzene ring of phenol?

    • 5
    • 4
    • 6
    • 1

19. Which reagent gives a white precipitate with phenol but not with benzene?

    • Acidified potassium dichromate(VI)
    • Dilute sodium hydroxide
    • Bromine water
    • Tollens' reagent

20. Phenol reacts with aqueous sodium hydroxide. What does this reaction show?

    • Phenol forms a precipitate of sodium phenol
    • Phenol is a base that accepts protons from sodium
    • Phenol is reduced by sodium hydroxide to benzene
    • Phenol is weakly acidic and forms sodium phenoxide and water

Related quizzes

• Bonding and stability of benzene Quiz · 18A.1 · 20 questions
• Electrophilic substitution of benzene Quiz · 18A.2 · 20 questions
• Amines: identification, basicity and reactions Quiz · 18B.1 · 20 questions
• Preparing amines and amides Quiz · 18B.2 · 20 questions
• Polyamides and amino acids Quiz · 18B.3 · 20 questions
• Proteins and the peptide bond Quiz · 18B.4 · 20 questions
• Deducing formulae from data Quiz · 18C.1 · 20 questions
• Planning multi-step reaction schemes Quiz · 18C.2 · 20 questions
• Practical preparation and purification Quiz · 18C.3 · 20 questions
• Sub-atomic particles, isotopes and relative masses Quiz · 1.1.1 · 20 questions