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IGCSE · Practice questions · Alkenes

Open the double bond.

Six original Cambridge-style questions on the alkenes and their addition reactions.

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

Test, then add.

01
Recall
[3 marks]

Describe a test to show that ethene is unsaturated but ethane is not. Give the reagent and both results.

  • Shake each gas with aqueous bromine (bromine water). ✓
  • Ethene: orange to colourless. ✓
  • Ethane: stays orange. ✓
02
Recall
[2 marks]

Give the molecular formula and structural formula of propene.

  • C3H6. ✓
  • CH3CH=CH2. ✓
03
Apply
[2 marks]

(Extended) Write an equation for the reaction of ethene with bromine and name the product.

  • CH2=CH2 + Br2 → CH2BrCH2Br. ✓
  • 1,2-dibromoethane. ✓
04
Recall
[3 marks]

(Extended) State the conditions used to make ethanol from ethene and write the equation.

  • Steam with an acid catalyst (phosphoric acid). ✓
  • 300 °C and 6000 kPa. ✓
  • C2H4 + H2O → C2H5OH. ✓
05
Apply
[3 marks]

(Extended) But-1-ene, CH2=CHCH2CH3, reacts with hydrogen. Name the catalyst, give the structural formula of the product and name it.

  • Nickel catalyst. ✓
  • CH3CH2CH2CH3. ✓
  • Butane. ✓
06
Analysis
[2 marks]

(Extended) Explain why the reaction of ethene with bromine is called an addition reaction, while the reaction of ethane with chlorine is a substitution reaction.

  • Ethene: the C=C opens and both bromine atoms add on, giving a single product. ✓
  • Ethane: a hydrogen atom is replaced by a chlorine atom, so two products form (chloroethane and hydrogen chloride). ✓

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.