Knowledge Organiser: Crude Oil & Fractional Distillation
Key Terms
- Crude oil — mixture of hydrocarbons
- Hydrocarbon — contains C and H only
- Fraction — group with similar bp
- Fractional distillation — physical separation by bp
Column Position Rules
- Top = small, low bp, flammable, runny
- Bottom = large, high bp, less flammable, viscous
- Hot at bottom, cool at top
- Gases exit at the very top
Fractions (top to bottom)
- Refinery gases (C1-C4) — heating/fuel
- Petrol (C5-C10) — cars
- Kerosene — jet fuel
- Diesel — vehicles/heating
- Bitumen — roads
Exam Checklist
- Physical process — no bonds broken
- Smaller = lower bp = higher up column
- Crude oil = finite, non-renewable
- Separated by boiling points
Key Equations
- Alkanes general formula: CₙH₂ₙ₊₂
- Complete combustion: CₙH₂ₙ₊₂ + O₂ → CO₂ + H₂O
- Fractions separated by boiling point — no chemical reaction involved
Common Mistakes
- Saying fractional distillation is a chemical process: It is a PHYSICAL separation — no bonds are broken; hydrocarbons are not chemically changed
- Getting column position wrong: Small molecules (short chains) have LOW boiling points and rise to the TOP of the column — large molecules stay at the bottom
- Saying crude oil is renewable: Crude oil is a finite, non-renewable fossil fuel — it cannot be replaced on human timescales
- Confusing fractions and compounds: Each fraction is a MIXTURE of hydrocarbons with similar boiling points — not a single pure compound
Memory Aid
- F — more Flammable
- I — fewer (weaker) forces between molecules
- L — Less viscous (runnier)
- M — smaller Molecule size
- S — lower boiling point (Smaller Bp)