Knowledge Organiser: Alkanes
Part of Alkanes · GCSE GCSE Chemistry revision
This topic summary covers Knowledge Organiser: Alkanes within Alkanes for GCSE Chemistry. Topic 38: Alkanes It is section 12 of 12 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 12 of 12
Practice
20 questions
Recall
0 flashcards
Knowledge Organiser: Alkanes
Key Terms
- Alkane — saturated hydrocarbon, CₙH₂ₙ₊₂
- Saturated — single C-C bonds only
- Homologous series — family with same general formula
- General formula — CₙH₂ₙ₊₂
First Four Alkanes (MEPB)
- Methane — CH₄ (gas)
- Ethane — C₂H₆ (gas)
- Propane — C₃H₈ (gas)
- Butane — C₄H₁₀ (gas)
Properties
- Longer chain = higher bp
- Immiscible with water
- Good fuels (combust in O₂)
- Relatively unreactive
Exam Checklist
- Saturated = single bonds, NOT "full of H"
- Use CₙH₂ₙ₊₂ for formulas
- Carbon always makes 4 bonds
- Alkanes vs alkenes: sat vs unsat
Key Equations
- General formula: CₙH₂ₙ₊₂ (n = number of carbons)
- CH₄ + 2O₂ → CO₂ + 2H₂O (complete combustion of methane)
- C₄H₁₀ + 6½O₂ → 4CO₂ + 5H₂O (complete combustion of butane)
Common Mistakes
- Saying saturated means "full of hydrogen": Saturated means the molecule contains ONLY single C-C bonds — no double bonds
- Using the wrong general formula: Alkanes = CₙH₂ₙ₊₂; alkenes = CₙH₂ₙ — confusing these loses formula marks
- Forgetting carbon makes 4 bonds: Every carbon atom in a structural formula must have exactly 4 bonds — check this before drawing any structure
- Saying alkanes decolourise bromine water: Alkanes do NOT decolourise bromine water — only alkenes do (they have a C=C double bond for addition reactions)
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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.
Quick Recall Flashcards
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