This exam tips covers Exam Tips: 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 13 of 14 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
💡 Exam Tips: Alkenes
🎯 Common Question Types:
- Write the molecular formula for a named alkene (1 mark)
- Describe the bromine water test for unsaturation (2 marks)
- Write an addition reaction equation (2 marks)
- Explain what unsaturated means (1-2 marks)
📝 Key Command Words:
- Describe: State the observation (colour change) and conclusion
- Explain: Link to C=C double bond and addition reaction
- Write: Show the double bond opening in the equation
⚠️ Common Mistakes to Avoid:
- Using CₙH₂ₙ₊₂ (alkane formula) for alkenes
- Saying bromine water "changes colour" — say "decolourised"
- Defining unsaturated as "reactive" — must say "C=C double bond"
Quick Check: What is the molecular formula of propene?
Using CₙH₂ₙ with n=3: H = 2×3 = 6. Formula = C₃H₆.
Quick Check: Write the equation for the reaction of propene with bromine water.
C₃H₆ + Br₂ → C₃H₆Br₂. Propene reacts with bromine in an addition reaction across the C=C double bond, producing 1,2-dibromopropane. The orange bromine water is decolourised.
Practice questions for Alkenes
What is the general formula for alkenes?
Explain what is meant by the term 'unsaturated' when applied to alkenes.