🎯 Common Question Types:
- Write a cracking equation given one product (2 marks)
- Describe the bromine water test for alkenes (2 marks)
- Explain why cracking is economically important (2 marks)
- Compare thermal and catalytic cracking (3 marks HT)
📝 Key Command Words:
- Write: Balance by atom conservation (C then H)
- Describe: State colour change and what it means
- Explain: Link to supply/demand and polymer production
⚠️ Common Mistakes to Avoid:
- Forgetting to include an alkene in cracking products
- Confusing cracking with combustion (no oxygen in cracking)
- Not checking atom balance on both sides of equation
Quick Check: Decane (C₁₀H₂₂) is cracked to form pentene (C₅H₁₀) and another product. Identify the other product.
C₁₀H₂₂ → C₅H₁₀ + ?. Carbons remaining: 10 - 5 = 5. Hydrogens remaining: 22 - 10 = 12. C₅H₁₂ — check with alkane formula: 2(5)+2 = 12 ✓. The other product is pentane (C₅H₁₂), an alkane.
Quick Check: Bromine water is added to two hydrocarbons, A and B. A decolourises the bromine water; B does not. What can you conclude about A and B?
A contains a C=C double bond — it is an alkene (unsaturated). It undergoes an addition reaction with bromine, decolourising it. B has no C=C double bond — it is an alkane (saturated). It does not react with bromine water at room temperature.
This exam tips covers Exam Tips: Cracking within Cracking (HT) for GCSE Chemistry. Revise Cracking (HT) in Organic Chemistry for GCSE Chemistry with 24 exam-style questions and 15 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. 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.
Practice questions for Cracking (HT)
What is cracking in chemistry?
Describe the conditions used in thermal cracking and state the types of product formed.