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Carbon Compounds and Fuels
6.1 Organic Chemistry Fundamentals
Carbon's uniqueness stems from two properties:
- Catenation: Carbon atoms can link with each other in long chains, rings, and branches, forming millions of compounds.
- Tetravalency: Carbon has 4 valence electrons, forming 4 covalent bonds.
Homologous Series: Series of organic compounds with the same functional group differing by −CH₂− unit.
| Series | Formula | Example | Functional Group |
|---|---|---|---|
| Alkanes | CₙH₂ₙ₊₂ | Methane CH₄, Ethane C₂H₆, Propane C₃H₈ | None (saturated) |
| Alkenes | CₙH₂ₙ | Ethene C₂H₄, Propene C₃H₆ | C=C (one double bond) |
| Alkynes | CₙH₂ₙ₋₂ | Ethyne C₂H₂ (acetylene) | C≡C (triple bond) |
| Alcohols | CₙH₂ₙ₊₁OH | Methanol CH₃OH, Ethanol C₂H₅OH | −OH |
| Carboxylic acids | CₙH₂ₙ₊₁COOH | Acetic acid CH₃COOH | −COOH |
Important compounds:
- Ethanol (C₂H₅OH): Used in alcoholic drinks, fuel (ethanol blending programme — 20% target by 2025 in India), antiseptic, solvent.
- Acetic acid (CH₃COOH): In vinegar (5% solution); used in food preservation, dyes, plastics.
- Formaldehyde (HCHO): Preservative in biological specimens; used in making Bakelite plastic.
6.2 Polymers
Natural polymers: Rubber (polyisoprene), starch (glucose polymer), cellulose (glucose polymer — structural), proteins (amino acid polymer), DNA/RNA (nucleotide polymer).
Synthetic polymers:
| Polymer | Monomer | Year | Uses |
|---|---|---|---|
| Bakelite | Phenol + formaldehyde | 1907 (Leo Baekeland) | Electrical switches, handles — first fully synthetic plastic |
| Nylon-6,6 | Adipic acid + hexamethylenediamine | 1935 (DuPont) | Fabric, ropes, toothbrush bristles |
| Polyethylene (PE) | Ethylene (ethene) | 1933 | Bags, pipes, bottles |
| PVC | Vinyl chloride | 1920s | Pipes, cables, flooring |
| Teflon (PTFE) | Tetrafluoroethylene | 1938 (Roy Plunkett) | Non-stick cookware, gaskets |
| Polystyrene | Styrene | 1839 | Packaging foam (thermocol), disposables |
Rubber Vulcanisation
Natural rubber is soft and sticky — unusable at extreme temperatures. Charles Goodyear (1839) discovered that heating rubber with sulphur (3–5%) creates cross-links between polymer chains, giving it elastic resilience over a wide temperature range.
Vulcanised rubber is used in tyres, seals, footwear.
6.3 Fuels and Energy
Calorific value = energy released per unit mass of fuel (MJ/kg):
| Fuel | Calorific Value (MJ/kg) | State | Characteristics |
|---|---|---|---|
| Hydrogen | 142 | Gas | Highest; zero-emission; storage challenge |
| LPG (butane/propane) | ~50 | Gas/liquid | Domestic cooking; burns cleanly |
| Petrol (gasoline) | ~47 | Liquid | Transport; octane rating (RON) |
| Diesel | ~45 | Liquid | Higher energy density; heavier vehicles |
| Kerosene | ~43 | Liquid | Aviation (jet fuel), rural cooking |
| Coal (bituminous) | ~28–35 | Solid | Power generation; CO₂ emitter |
| Wood | ~15 | Solid | Biomass; rural energy; inefficient |
| Biogas | ~22 | Gas | Mixture of CH₄ (55–60%) + CO₂; from organic waste |
Petroleum Refining — Fractional Distillation Products:
| Fraction | Boiling Range | Carbon Atoms | Uses |
|---|---|---|---|
| Refinery gas (LPG) | Below 30°C | C₁–C₄ | Cooking, heating |
| Petrol | 30–70°C | C₅–C₇ | Motor cars |
| Naphtha | 90–200°C | C₆–C₁₀ | Chemical feedstock |
| Kerosene | 150–270°C | C₁₀–C₁₆ | Jet fuel, rural cooking |
| Diesel | 250–350°C | C₁₄–C₁₉ | Trucks, trains, buses |
| Fuel oil | Above 350°C | C₂₀+ | Ships, power stations |
| Bitumen/Asphalt | Residue | C₄₀+ | Road construction, roofing |
India's Ethanol Blending Programme (EBP)
Government target: 20% ethanol in petrol (E20) by 2025–26 (advanced from 2030).
- Purpose: reduce petroleum imports, lower vehicular emissions, support sugarcane farmers
- In FY2023–24, India achieved ~12% blending nationally
- Bioethanol is produced from sugarcane molasses, damaged grain, and cellulosic biomass