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Grade 10 Advanced About 15 min Version 1 Awaiting review Premium

Hydrocarbons: alkanes, alkenes and alkynes

Hydrocarbons are compounds of carbon and hydrogen only. They are the main substances in natural gas, LPG, petrol and kerosene. Each carbon atom makes four bonds. In alkanes (general formula CₙH₂ₙ₊₂) all the carbon-carbon bonds are single: they are saturated. Alkenes (CₙH₂ₙ) have one carbon-carbon double bond and alkynes (CₙH₂ₙ₋₂) have a triple bond: they are unsaturated. Unsaturated hydrocarbons react with orange bromine water and turn it colourless; alkanes do not.

What you will learn

  • Recognise alkanes, alkenes and alkynes from their formulas and models.
  • Use bromine water to tell saturated from unsaturated hydrocarbons.
  • Describe everyday uses of hydrocarbons.

Before you start

  • Know that carbon forms four covalent bonds.

Materials

  • Molecular model kit, bromine water (shown by the teacher)

Equipment

  • Molecular model kit

Procedure

  1. Choose a card and build its model: are there any double or triple bonds?
  2. Shake a sample with bromine water and watch the colour.
  3. Place each card in the alkanes, alkenes or alkynes group.