Chemical reactions of the alkenes
3 marks · NormalAlkenes are described as unsaturated hydrocarbons.
Explain what 'unsaturated' means and how you can test for unsaturation using a chemical reaction.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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Also accept: Accept bromine water as test, stating it decolourises
Common mistakes: Not mentioning C=C bonds; Incorrectly stating bromine water turns orange
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Marking points
B1 · 1 mark · Identifies unsaturated compounds have C=C double bonds (or not the maximum H atoms).
B2 · 1 mark · States that bromine water (or bromine) is the chemical test for unsaturation.
B3 · 1 mark · Describes the positive result: bromine water is decolourised or changes from orange/brown to colourless.
Worked solution
'Unsaturated' means that the compound contains C=C double bonds (and not the maximum possible H atoms).
You can test for unsaturation by adding bromine water to the substance. If the substance is unsaturated, the bromine water changes from orange/brown to colourless.