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IGCSE · Practice questions · Alkanes

Burn or substitute.

Six original Cambridge-style questions on the alkanes.

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

Two reactions only.

01
Recall
[2 marks]

State the general formula of the alkanes and explain why they are described as saturated.

  • CnH2n+2. ✓
  • They contain only single carbon-carbon bonds (no C=C). ✓
02
Apply
[2 marks]

Write a balanced equation for the complete combustion of butane, C4H10.

  • C4H10 + 6½O2 → 4CO2 + 5H2O (O on the right = 8 + 5 = 13). ✓
  • Doubled: 2C4H10 + 13O2 → 8CO2 + 10H2O. ✓
03
Calc
[2 marks]

30 cm3 of propane is burned completely: C3H8 + 5O2 → 3CO2 + 4H2O. Calculate the volume of oxygen used and the volume of carbon dioxide made, all volumes at room temperature and pressure.

  • Oxygen: 5 × 30 = 150 cm3. ✓
  • Carbon dioxide: 3 × 30 = 90.0 cm3. ✓
04
Apply
[3 marks]

Ethane reacts with chlorine. State the condition needed, write the equation and name the organic product.

  • Ultraviolet light. ✓
  • C2H6 + Cl2 → C2H5Cl + HCl. ✓
  • Chloroethane. ✓
05
Explain
[2 marks]

(Extended) A mixture of methane and chlorine is kept in the dark and nothing happens. When it is placed in sunlight, it reacts. Explain these observations.

  • The reaction is photochemical. ✓
  • Ultraviolet light (in sunlight) provides the activation energy needed to start the reaction; in the dark there is not enough energy. ✓
06
Analysis
[2 marks]

A student writes CH4 + Cl2 → CH4Cl2 and calls it addition. Identify two errors.

  • Methane is saturated, so it reacts by substitution, not addition. ✓
  • The products are CH3Cl and HCl: one hydrogen is replaced and leaves as hydrogen chloride (CH4Cl2 would need carbon to make six bonds). ✓

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.