Alkanes and Alkenes: The First Homologous Series · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Two families, one double bond apart

Science · Matter & Materials · ages 15-16
Name ______________________   Date ____________

  1. What is the formula of propane?

    • C3H6
    • C4H10
    • C3H8

  2. Which is the general formula of the alkanes?

    • CnH2n+2
    • CnH2n
    • CnH2n-2

  3. Bromine water stays orange when shaken with an alkane.

    Circle one:   True   False

  4. What makes a set of compounds a homologous series?

    • The same colour and smell throughout
    • The same carbon count in each member
    • The same general formula, with members differing by CH2

  5. Propene is shaken with bromine water. What happens?

    • It turns colourless
    • It stays orange
    • It turns green

  6. Methane burns in a short air supply. Which products fit?

    • Carbon dioxide and water only
    • Carbon monoxide, soot and water
    • Carbon dioxide and hydrogen only

  7. Why does incomplete combustion give CO instead of CO2?

    • Too much oxygen cools the flame
    • Too little oxygen is available to finish the burn
    • Hydrocarbons hold no hydrogen

  8. How would you show a gas sample is propene and not propane?

    • Shake it with bromine water and watch it turn colourless
    • Burn it and weigh the ash
    • Mix it with water and test the pH
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Two families, one double bond apart W1-mt_mkLJDtBanL-s1

  1. C3H8 · Propane has three carbons, so CnH2n+2 gives C3H8.
  2. CnH2n+2 · Every alkane fits CnH2n+2, from methane upwards.
  3. True · Single bonds ignore bromine in the cold, so the orange colour stays.
  4. The same general formula, with members differing by CH2 · One formula plus a CH2 step between members defines the series.
  5. It turns colourless · The double bond adds bromine, so the orange colour vanishes.
  6. Carbon monoxide, soot and water · Too little oxygen leaves the burn unfinished, giving CO and soot.
  7. Too little oxygen is available to finish the burn · Each carbon needs enough oxygen to reach CO2, and a short supply stops at CO.
  8. Shake it with bromine water and watch it turn colourless · Only the alkene decolourises bromine water, so colourless proves propene.
Worksheet · LightMySky