AlkenesAQA A-Level Chemistry: Topic test

1. 1
   Pent-1-ene, CH₂=CHCH₂CH₂CH₃, and pentane are both colourless liquids. A student shakes a few drops of each liquid with separate portions of orange bromine water.

   (a)

   What is observed when pent-1-ene is shaken with bromine water?

   [1 mark]

   • AThe mixture stays orange
   • BThe mixture turns colourless
   • CThe mixture turns green
   • DA white precipitate forms

   (b)

   What is the organic product of the reaction between pent-1-ene and bromine?

   [1 mark]

   • A1-Bromopentane
   • B2-Bromopentane
   • C1,1-Dibromopentane
   • D1,2-Dibromopentane

   (c)

   Explain why bromine reacts with pent-1-ene but not with pentane.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Poly(tetrafluoroethene), PTFE, is used to coat non-stick frying pans. It is made by addition polymerisation of tetrafluoroethene, CF₂=CF₂.

   (a)

   What is the repeating unit of PTFE?

   [1 mark]

   • A–CF₂–CF₂–
   • B–CF=CF–
   • C–CF₂–CF₂–CF₂–
   • D–CF₃–CF₃–

   (b)

   Which are the only significant intermolecular forces between PTFE chains?

   [1 mark]

   • AHydrogen bonds
   • BPermanent dipole–dipole forces
   • CLondon forces (induced dipole–induced dipole)
   • DIonic attractions

   (c)

   Explain why PTFE is chemically unreactive.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Pent-1-ene, CH₂=CHCH₂CH₂CH₃, reacts with hydrogen bromide at room temperature to form two isomeric bromopentanes. The major product is 2-bromopentane.

   (a)

   Explain, with reference to carbocation intermediates, why 2-bromopentane is the major product.

   [3 marks]

   (b)

   Describe the mechanism for the formation of 2-bromopentane, stating where each curly arrow starts and finishes.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   But-1-ene, CH₂=CHCH₂CH₃, is a gas at room temperature. It reacts rapidly with bromine, and it can also be used as a monomer to make poly(but-1-ene), a polymer used for hot-water pipes.

   (a)

   Describe the mechanism for the reaction of but-1-ene with bromine, and state what is observed when but-1-ene is bubbled through bromine water.

   [6 marks]

   (b)

   Describe how poly(but-1-ene) is formed from but-1-ene, give its repeating unit and explain why the polymer is unreactive and why its chains attract one another.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   Ethene, CH₂=CH₂, is bubbled into concentrated sulfuric acid, H₂SO₄, at room temperature. A product with the formula CH₃CH₂OSO₂OH is formed by electrophilic addition.

   (a)

   What is the role of the sulfuric acid molecule in the first step of the mechanism?

   [1 mark]

   • AA nucleophile donating a lone pair to the C=C bond
   • BA base accepting a proton from ethene
   • CAn electrophile accepting a pair of electrons from the C=C bond
   • DA dehydrating agent removing water from ethene

   (b)

   Which is the correct structural formula of the product?

   [1 mark]

   • ACH₃CH₂OSO₂OH
   • BCH₃CH₂SO₃H
   • CCH₃CH₂OH
   • DCH₂=CHOSO₂OH

   (c)

   Describe, in words, the first step of the mechanism for this reaction, stating where each curly arrow starts and finishes.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   A section of poly(propenenitrile), a polymer used to make acrylic fibres for clothing and carpets, has the structure –CH₂–CH(CN)–CH₂–CH(CN)–CH₂–CH(CN)–.

   (a)

   Which compound is the monomer from which this polymer is made?

   [1 mark]

   • ACH₃CH₂CN
   • BCH₂=C(CN)₂
   • CCH₃CH=CHCN
   • DCH₂=CHCN

   (b)

   Which statement about the polymer chain is correct?

   [1 mark]

   • AIt contains C=C bonds, so it decolourises bromine water
   • BIt has only single bonds along the carbon chain, so it does not decolourise bromine water
   • CIt contains C≡N bonds, so it is an alkene
   • DIt is a condensation polymer because it contains a nitrile group

   (c)

   Explain why the intermolecular forces between chains of poly(propenenitrile) are stronger than those between chains of poly(ethene).

   [2 marks]

   Total for question 6: 4 marks

7. 7
   Cyclohexene, C₆H₁₀ (Mr = 82.0), reacts with bromine in an inert solvent to form 1,2-dibromocyclohexane, C₆H₁₀Br₂ (Mr = 241.8). A student adds 4.10 g of cyclohexene to an excess of bromine.

   (a)

   Calculate the maximum mass of 1,2-dibromocyclohexane that can be formed.

   [3 marks]

   (b)

   The student obtains 9.67 g of 1,2-dibromocyclohexane. Calculate the percentage yield, and explain why the atom economy for the formation of 1,2-dibromocyclohexane from cyclohexene and bromine is 100%.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   2-Methylpropene, CH₂=C(CH₃)₂, is a gas used to make poly(2-methylpropene), a polymer used as an airtight lining inside tyres. 2-Methylpropene also reacts with hydrogen bromide. A manufacturer wants to check whether a sample of the polymer contains traces of unreacted monomer.

   (a)

   Explain, using the mechanism, why the reaction of 2-methylpropene with hydrogen bromide gives 2-bromo-2-methylpropane as the major product and 1-bromo-2-methylpropane as the minor product.

   [6 marks]

   (b)

   Give the repeating unit of poly(2-methylpropene). Describe a test that would show whether the polymer sample contains unreacted monomer, stating the result for a sample with and without monomer, and explain why the pure polymer is unreactive.

   [6 marks]

   Total for question 8: 12 marks

End of questions