This exam tips covers Exam Tips: Crude Oil within Crude Oil for GCSE Chemistry. Topic 37: Crude Oil It is section 12 of 13 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
💡 Exam Tips: Crude Oil
🎯 Common Question Types:
- Explain why fractional distillation separates crude oil (3 marks)
- Describe the trend in properties going up the column (2 marks)
- Give a use for a named fraction (1 mark)
- Explain what "finite resource" means (1 mark)
📝 Key Command Words:
- Explain: Boiling points, forces between molecules, condensation point
- State: Name the fraction and its position in the column
- Describe: Physical process — no bonds broken
⚠️ Common Mistakes to Avoid:
- Saying small molecules are at the bottom (they are at the top)
- Calling fractional distillation a chemical process
- Forgetting that crude oil is a mixture, not a pure substance
Quick Check: Why is petrol collected higher up the fractionating column than diesel?
Petrol molecules are smaller (C5-C10) than diesel molecules. Smaller molecules have weaker forces between molecules and a lower boiling point, so they need to rise higher up the column (where it is cooler) before they reach their boiling point and condense.
Quick Check: Is fractional distillation a physical or chemical process? Explain your answer.
It is a physical process. The hydrocarbon molecules are separated by their different boiling points, but no chemical bonds are broken or formed. The molecules themselves are chemically unchanged — they are just sorted by size.
Practice questions for Crude Oil
A hydrocarbon is a compound that contains only:
Explain how fractional distillation separates crude oil into different fractions.