Organic Chemistry Basics
Alkanes, alkenes, crude oil, polymers and their uses in Pakistan
Organic chemistry = chemistry of carbon compounds. Carbon can form 4 bonds and chains of any length.
Alkanes (CₙH₂ₙ₊₂): Saturated — single bonds only. Methane (CH₄), ethane (C₂H₆), propane (C₃H₈).
Alkenes (CₙH₂ₙ): Unsaturated — contain C=C double bond. Ethene (C₂H₄).
Crude oil: Mixture of hydrocarbons separated by **fractional distillation**. Smaller molecules → lower boiling point → collected higher up the column.
Fractions (top to bottom): refinery gas → petrol → kerosene (jet fuel) → diesel → fuel oil → bitumen.
Cracking: Breaks large alkane molecules into smaller alkenes + alkanes using heat and catalyst. Increases supply of petrol and ethene for plastics.
Addition polymers: Alkene monomers join together: n(CH₂=CH₂) → (−CH₂−CH₂−)ₙ (polyethene/polythene).
Environmental impact: Burning fossil fuels → CO₂ (greenhouse gas), CO (toxic), SO₂ (acid rain).
Key Points to Remember
- 1Alkanes saturated (single bonds); alkenes unsaturated (C=C)
- 2Bromine water test decolourises with alkenes
- 3Crude oil separated by fractional distillation
- 4Addition polymerisation: alkene monomers → long chain polymer
Pakistan Example
PARCO Refinery and Plastic Bags — Pakistan's Organic Chemistry
Pakistan's PARCO (Pak-Arab Refinery) and Attock Refinery fractionally distil crude oil daily. Petrol, kerosene (used in lamps in rural Pakistan), and LPG (cooking gas cylinders) are all fractions. Every plastic shopping bag is polyethene — addition polymer of ethene from cracking. Pakistan's 2019 plastic bag ban is rooted in environmental organic chemistry.