very-high Bromine water test (2 marks): Say "decolourised" not just "changes colour". Must state the observation AND the conclusion.
very-high Formula questions (1-2 marks): Use CₙH₂ₙ. Common trap: choosing the alkane formula CₙH₂ₙ₊₂ by mistake.
high Addition reaction equations (2 marks): Show product clearly — double bond becomes single, one atom from each reactant bonds to each carbon.
high Unsaturated definition (1-2 marks): "Contains a C=C double bond" — must be this specific, not just "reactive".
Edexcel 1CH0: Examined in Paper 2 (1CH0/2). Addition reactions of alkenes (with water, halogens, hydrogen) and the bromine water test are key Edexcel exam points. In Edexcel-style questions, the command word "Suggest" appears frequently — use your chemistry knowledge to apply to an unfamiliar context.
This exam focus covers Exam Focus: Alkenes within Alkenes for GCSE Chemistry. Revise Alkenes in Organic Chemistry for GCSE Chemistry with 20 exam-style questions and 15 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 12 of 14 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
Practice questions for Alkenes
What is the general formula for alkenes?
Explain what is meant by the term 'unsaturated' when applied to alkenes.