Knowledge Organiser: Alcohols
Key Terms
- Functional group — -OH (hydroxyl)
- General formula — CₙH₂ₙ₊₁OH
- Fermentation — glucose → ethanol + CO₂
- Hydration — ethene + steam → ethanol
First Four Alcohols
- Methanol — CH₃OH (toxic!)
- Ethanol — C₂H₅OH (drinks)
- Propanol — C₃H₇OH (sanitiser)
- Butanol — C₄H₉OH (industrial)
Fermentation vs Hydration
- Fermentation: renewable, slow, low purity, anaerobic
- Hydration: non-renewable, fast, high purity, 300°C/70atm
Exam Checklist
- Fermentation: don't forget CO₂ product
- Functional group: -OH with dash
- Methanol = TOXIC (not drinkable)
- Fermentation = anaerobic (no oxygen)
Key Equations
- C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ (fermentation of glucose)
- C₂H₄ + H₂O → C₂H₅OH (hydration of ethene)
- C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O (complete combustion of ethanol)
- General formula: CₙH₂ₙ₊₁OH
Common Mistakes
- Forgetting CO₂ in fermentation: Fermentation produces BOTH ethanol AND carbon dioxide — missing CO₂ loses a mark
- Saying fermentation needs oxygen: Fermentation is an ANAEROBIC process — it occurs without oxygen; oxygen would allow aerobic respiration instead
- Confusing methanol and ethanol: Methanol (CH₃OH) is TOXIC — even small amounts cause blindness or death; ethanol (C₂H₅OH) is the alcohol in drinks
- Saying hydration uses a biological catalyst: Hydration of ethene uses a phosphoric acid (H₃PO₄) catalyst at ~300°C and 70 atm — not enzymes (that is fermentation)
Memory Aid
- Functional group = -OH (hydroxyl) — always at the end of the chain
- Naming = same prefix as alkane + "-anol" ending