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AS · Practice questions · Alkenes

Add across the double bond.

Six original Cambridge-style questions on the preparation and reactions of alkenes.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

The π bond adds; hot KMnO4 splits.

01
Recall
[3 marks]

Give the reagents and conditions for converting ethene into (a) ethane, (b) ethanol, (c) 1,2-dibromoethane.

  • (a) H2, Ni catalyst, about 150 °C. ✓
  • (b) steam, H3PO4 catalyst, 300 °C and 6 MPa. ✓
  • (c) Br2 at room temperature. ✓
02
Recall
[2 marks]

Describe a chemical test to distinguish hexane from hex-1-ene.

  • Add bromine water and shake. ✓
  • Hex-1-ene decolourises it (orange to colourless); hexane does not (in the dark). ✓
03
Analysis
[3 marks]

An alkene C5H10 is heated with concentrated acidified KMnO4, giving butanoic acid and carbon dioxide. Deduce the alkene.

  • CO2 comes from a =CH2 end. ✓
  • Butanoic acid comes from =CHCH2CH2CH3. ✓
  • The alkene is pent-1-ene, CH2=CHCH2CH2CH3. ✓
04
Recall
[2 marks]

Write equations for the formation of ethene from (a) ethanol and (b) bromoethane, with conditions.

  • (a) C2H5OH → C2H4 + H2O; heated Al2O3 or hot concentrated H2SO4. ✓
  • (b) C2H5Br + NaOH → C2H4 + NaBr + H2O; NaOH in ethanol, heat. ✓
05
Analysis
[2 marks]

Give the products of oxidising 2-methylpropene with (a) cold, dilute and (b) hot, concentrated acidified KMnO4.

  • (a) 2-methylpropane-1,2-diol, (CH3)2C(OH)CH2OH. ✓
  • (b) propanone and carbon dioxide. ✓
06
Explain
[2 marks]

Explain why alkenes are more reactive than alkanes.

  • The C=C contains a π bond, which is weaker than a σ bond. ✓
  • The π electrons are exposed above and below the plane, a region of high electron density that attracts electrophiles. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.