This exam tips covers Exam Tips: Alkanes within Alkanes for GCSE Chemistry. Topic 38: Alkanes It is section 11 of 12 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
💡 Exam Tips: Alkanes
🎯 Common Question Types:
- Give the molecular formula of a named alkane (1 mark)
- Explain what "saturated" means (1-2 marks)
- Draw the displayed formula of propane (2 marks)
- Explain why butane has a higher boiling point than methane (2 marks)
📝 Key Command Words:
- Explain: Link to single bonds and forces between molecules
- Draw: Show each bond as a line, every C must have 4 bonds
- State: Give the formula or name directly
⚠️ Common Mistakes to Avoid:
- Saying saturated means "full of energy" — it means single bonds only
- Drawing carbon with more or fewer than 4 bonds
- Using CₙH₂ₙ (alkene formula) instead of CₙH₂ₙ₊₂
Quick Check: What is the molecular formula of pentane (an alkane with 5 carbons)?
Using CₙH₂ₙ₊₂ with n=5: H = 2(5)+2 = 12. Formula = C₅H₁₂.
Quick Check: Explain in one sentence what "saturated" means for an alkane.
A saturated hydrocarbon contains only single carbon-carbon bonds, meaning no double bonds are present and each carbon atom is bonded to the maximum possible number of hydrogen atoms.
Practice questions for Alkanes
What is the general formula for the alkane homologous series?
Explain why the boiling point of alkanes increases as the chain length increases.