Organic Chemistry
Hydrocarbons, alkanes, alkenes, ethanol, polymers and plastics
Organic chemistry = chemistry of carbon compounds.
Alkanes (CₙH₂ₙ₊₂): Saturated hydrocarbons (single bonds only). Methane CH₄, ethane C₂H₆. Undergo combustion and substitution reactions. Relatively unreactive.
Alkenes (CₙH₂ₙ): Unsaturated (contain C=C double bond). Ethene C₂H₄. More reactive than alkanes. Undergo addition reactions: with bromine (decolourises bromine water — test for unsaturation), hydrogen (hydrogenation), steam (makes ethanol).
Crude oil is a mixture of hydrocarbons separated by fractional distillation — shorter chains boil at lower temperatures (gases at top, bitumen at bottom).
Cracking: Breaking long-chain alkanes into shorter, more useful alkenes + alkanes. Uses heat + catalyst (catalytic cracking) or steam (thermal cracking).
Ethanol production: Fermentation (sugar + yeast, anaerobic, 37°C) or hydration of ethene (steam + ethene + catalyst).
Polymers: **Addition polymerisation** — alkene monomers join (e.g., ethene → polyethene/polythene). **Condensation** — monomers join releasing water (nylon, polyester).
Key Points to Remember
- 1Alkanes: saturated, single bonds, CnH2n+2
- 2Alkenes: unsaturated, C=C double bond, CnH2n
- 3Crude oil separated by fractional distillation
- 4Addition polymers from alkenes, condensation releases water
Pakistan Example
Plastic Bags and Crude Oil — Pakistan's Petrochemical Reality
Pakistan's Attock Refinery and PARCO fractionally distil crude oil daily. The polythene in every shopping bag is made by addition polymerisation of ethene. Pakistan's ban on thin plastic bags (2019) relates directly to the environmental persistence of these polymers — they don't biodegrade.