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chemistry igcse acapprinted 109 · PDF 109
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printed 109 · PDF 109
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109
Reaction: Alkenes react with hydrogen to form alkanes.
Conditions: Nickel catalyst at 150°C.
Example: C₂H₄ + H₂ → C₂H₆
Use: Used to hydrogenate vegetable oils, converting unsaturated fats to saturated fats.
Addition of Halogens (e.g., Bromination)
Reaction: Alkenes react with halogens (e.g., bromine, chlorine) to form dihaloalkanes.
Observation: Bromine water decolorizes (orange-brown to colorless), indicating the presence of
alkenes.
Example: C₂H₄ + Br₂ → C₂H₄Br₂
Hydration (Addition of Steam)
Reaction: Alkenes react with steam to form alcohols.
Conditions: Requires high temperature (300°C), high pressure (60-70 atm), and phosphoric acid
catalyst.
Example: C₂H₄ + H₂O → C₂H₅OH
Use: Industrially used to produce ethanol from ethene.
Alcohols
- Functional Group: -OH
- General Formula: Cₙ H₂ₙ ₊₁OH
Naming Examples:
- Methanol: CH₃OH
- Ethanol: C₂H₅OH
- Propanol: C₃H₇OH
Key Alcohol: Ethanol
- Combustion: C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O
Formation of Carboxylic Acids from Alcohols
Oxidation Using Oxidizing Agents
Reaction: Alcohols react with oxidizing agents (e.g., potassium dichromate in acidic conditions) to
produce carboxylic acids.
Conditions: Heat with acidified potassium dichromate (H₂SO₄).
Example: C₂H₅OH + [O] → CH₃COOH + H₂O
Microbial Oxidation