CAIE A Level Chemistry 9701 · An introduction to organic chemistry
Ethene reacts with bromine to form 1,2-dibromoethane. Explain, in terms of the type of reaction, the type of bond fission, and the role of the bromine molecule, why this reaction occurs readily and why it is not a free-radical substitution.
7 marks, so the mark scheme is looking for about 7 separate creditworthy points. Making the same point twice in different words earns it once.
Explain means: Give the reasons or the mechanism: why or how something happens. Link each point to the next with because, so or which means. A list of facts with no links usually loses the reasoning marks.
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