MYP Chemistry sample question: Alkanes, alkenes and combustion

Ethane (C₂H₆) is an alkane and ethene (C₂H₄) is an alkene.

1. (a)Describe a chemical test to distinguish ethene from ethane, and give the result for each.[3]
   Show the mark scheme for (a)

   • • Add bromine water (1)
   • • Ethene decolourises it, orange to colourless (1)
   • • Ethane causes no change (1)
2. (b)Write a balanced symbol equation for the complete combustion of ethane.[2]
   Show the mark scheme for (b)

   • • Products carbon dioxide and water (1)
   • • 2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O (1)

Check your equation by counting each element: 4 C, 12 H and 14 O on each side. Alkenes react with bromine because of the C=C double bond.