A student has unlabelled samples of three liquids. The student knows that the three liquids are: • pentane, C5H12 • pentene, C5H10 • ethanoic acid, CH3COOH. Describe tests that the student should do to identify each of the three liquids. Include balanced symbol equations for the reactions described. – 7569

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1. I would first add sodium carbonate to each sample. Ethanoic acid would fizz because it reacts with carbonate to give carbon dioxide, but pentane and pentene would not fizz.
   Next, I would add bromine water to separate samples of pentane and pentene and shake them. Pentene would make the bromine water change from orange to colourless because it reacts with bromine, but with pentane and ethanoic acid the bromine water would stay orange.
   The reactions are:
   2CH₃COOH + Na₂CO₃ → 2CH₃COONa + CO₂ + H₂O
   C₅H₁₀ + Br₂ → C₅H₁₀Br₂

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