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Halogenoalkanes test with answers for A Level chemistry (free PDF download)

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Quick answer: Alkanes react with halogens in UV light by free radical substitution, a chain reaction of initiation, propagation and termination. This Chemistry 11-12 test on halogenoalkanes has 8 questions worth 20 marks, to do in 45 minutes: radical substitution, mechanism and classify. The mark scheme is on a separate page; free printable PDF.

Halogenoalkanes test with answers for A Level chemistry (free PDF download)

This test checks the mechanisms, reagents and rates of halogenoalkane reactions. Answer all questions, give state symbols and curly arrows where relevant, and then show calculations. Also, you have 45 minutes, because the test is worth 20 marks.

Level: Chemistry grades 11-12 (A Level · IB · Class 11-12) · Curriculum: IB R3.4

Time: 45 minutes · 8 questions · Total: 20 marks · Calculator allowed

Question 1 Radical substitution (3 marks)

  1. Firstly, write the equation for the initiation step in the reaction of chlorine with methane. (1 mark)
  2. Then write the two propagation steps. (2 marks)
  3. Finally, write one termination step. (1 mark)

Question 2 Mechanism (3 marks)

SN2 mechanism: hydroxide ion attacks the carbon of bromoethane from the back with curly arrows, passes through a transition state and gives ethanol and bromideHO⁻CH₃CH₂–Br+[HO···C···Br]⁻transition stateProducts: CH₃CH₂OH + Br⁻one step: bond to OH forms as the C–Br bond breaksthe nucleophile attacks from the side opposite to bromine (inversion)
This mechanism shows the hydrolysis of bromoethane.
  1. Firstly, name the mechanism shown. (1 mark)
  2. Then state what the first curly arrow represents. (1 mark)
  3. Finally, state what happens to the configuration at a chiral carbon. (1 mark)

Question 3 Classify (1 mark)

  1. Firstly, classify 2-bromo-2-methylpropane as primary, secondary or tertiary. (1 mark)

Question 4 Comparing rates (3 marks)

  1. Firstly, place 1-chlorobutane, 1-bromobutane and 1-iodobutane in order of hydrolysis rate, fastest first. (1 mark)
  2. Then explain the order using bond enthalpy. (2 marks)

Question 5 Reagents (2 marks)

  1. Then state the reagent and conditions to convert bromoethane to propanenitrile. (2 marks)

Question 6 Percentage yield (3 marks)

  1. 6.00 g of 1-chlorobutane (Mr = 92.5) gives 3.10 g of butan-1-ol (Mr = 74.0) on hydrolysis, so calculate the percentage yield. (3 marks)

Question 7 SN1 or SN2 (3 marks)

  1. 2-bromo-2-methylpropane reacts by SN1, so first write its rate equation. (1 mark)
  2. Then explain why the rate does not depend on [OH⁻]. (2 marks)

Question 8 Ozone layer (2 marks)

  1. Finally, write the two steps showing how Cl• acts as a catalyst in ozone destruction. (2 marks)

See the halogenoalkanes test answers and mark scheme

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