📑 Topics on this page (Jump to Topic):
📌 1. Carbon & Its Allotropes
- Carbon has valency 4 (tetravalent) and forms covalent bonds. Catenation — the ability to form long chains with itself — gives millions of organic compounds.
- Carbon is the basis of all life; Wöhler synthesised urea in 1828, disproving the "vital force theory".
| Allotrope | Structure | Properties / uses |
|---|---|---|
| Diamond | Each C bonded to four C — 3-D network | Hardest, insulator, high refractive index; glass cutting, jewellery |
| Graphite | Hexagonal layers; each C bonded to three C | Soft, slippery, conducts electricity; pencil "lead", lubricant, electrodes, reactor moderator |
| Fullerene (C₆₀) | Football-like sphere — buckminsterfullerene | Nanotechnology |
| Graphene / carbon nanotubes | One-atom-thick sheet | Extremely strong and conductive |
- Amorphous forms: coal, lamp black, wood charcoal, coke, bone charcoal (decolourising sugar).
📌 2. Hydrocarbons & Functional Groups
| Class | General formula | Bond | Example |
|---|---|---|---|
| Alkane (saturated) | CₙH₂ₙ₊₂ | Single | Methane CH₄, ethane, propane, butane |
| Alkene (unsaturated) | CₙH₂ₙ | Double | Ethene C₂H₄ (ripening fruit) |
| Alkyne (unsaturated) | CₙH₂ₙ₋₂ | Triple | Ethyne/acetylene C₂H₂ (welding) |
- Homologous series: successive members differ by −CH₂ (14 u); similar chemical properties.
- Functional groups: −OH (alcohol), −CHO (aldehyde), >C=O (ketone), −COOH (carboxylic acid), −X (halo).
- Ethanol (C₂H₅OH, ethyl alcohol) — liquor, sanitiser, blended in petrol (E20). Methanol is poisonous — causes blindness/death. Denatured spirit = ethanol + methanol.
- Ethanoic acid (acetic acid) — vinegar = 5–8% solution; pure acetic acid freezes in winter — glacial acetic acid. Alcohol + acid → ester (fruity smell).
- Saponification: fat/oil + NaOH → soap + glycerol.
📌 3. Polymers, Fuels & Gases
| Polymer | Monomer / type | Uses |
|---|---|---|
| Polythene | Ethene | Bags, bottles |
| PVC | Vinyl chloride | Pipes, cable insulation |
| Teflon | Tetrafluoroethene | Non-stick cookware |
| Bakelite | Phenol + formaldehyde (thermosetting) | Switches, handles |
| Nylon | First synthetic fibre (polyamide) | Ropes, parachutes, socks |
| Natural rubber | Isoprene; vulcanised with sulphur (Goodyear) | Tyres |
| Cellulose / starch / protein / DNA | Natural polymers | — |
| Fuel | Main component |
|---|---|
| LPG | Butane + propane (ethyl mercaptan for smell) |
| CNG / biogas | Methane |
| Water gas | CO + H₂ |
| Producer gas | CO + N₂ |
| Marsh gas | Methane |
| Coal types (increasing carbon) | Peat < lignite < bituminous < anthracite |
- Fuel efficiency is measured by calorific value; hydrogen has the highest (≈150 kJ/g). Petrol quality — octane number; diesel — cetane number.
- Carbon monoxide — colourless, odourless, poisonous; binds haemoglobin forming carboxyhaemoglobin (deaths from braziers in closed rooms). Solid CO₂ = dry ice; CO₂ fire extinguishers.
⚠️ Exam Traps:
- Pencil "lead" is graphite, not lead.
- LPG is mainly butane; CNG is methane.
- Graphite conducts, diamond does not — both are carbon.
📌 4. Practice MCQs
📝 Practice MCQs (prepared by SF Prep — not PYQs)
Q1. Pencil "lead" is actually: Practice
Correct answer: (A)
Graphite is soft and layered.
Graphite is soft and layered.
Q2. Which allotrope of carbon conducts electricity? Practice
Correct answer: (C)
One free electron per C gives conductivity.
One free electron per C gives conductivity.
Q3. The main component of LPG is: Practice
Correct answer: (B)
Butane and propane; ethyl mercaptan added to detect leaks.
Butane and propane; ethyl mercaptan added to detect leaks.
Q4. CNG is mainly: Practice
Correct answer: (C)
Compressed Natural Gas — mainly CH₄.
Compressed Natural Gas — mainly CH₄.
Q5. Vinegar contains: Practice
Correct answer: (C)
5–8% ethanoic acid.
5–8% ethanoic acid.
Q6. The gas used to ripen fruits artificially is: Practice
Correct answer: (B)
Ethylene (ethene) is also a plant hormone.
Ethylene (ethene) is also a plant hormone.
Q7. Non-stick cookware is coated with: Practice
Correct answer: (D)
Polytetrafluoroethene (PTFE).
Polytetrafluoroethene (PTFE).
Q8. Rubber is vulcanised with: Practice
Correct answer: (C)
Discovered by Charles Goodyear; rubber becomes hard and durable.
Discovered by Charles Goodyear; rubber becomes hard and durable.
Q9. Sleeping in a closed room with a burning brazier can be fatal due to: Practice
Correct answer: (D)
CO binds haemoglobin and blocks oxygen transport.
CO binds haemoglobin and blocks oxygen transport.
Q10. The fuel with the highest calorific value is: Practice
Correct answer: (A)
≈ 150 kJ/g.
≈ 150 kJ/g.
Q11. The general formula of alkanes is: Practice
Correct answer: (C)
Saturated hydrocarbons with only single bonds.
Saturated hydrocarbons with only single bonds.
Q12. Which gas is used in gas welding? Practice
Correct answer: (A)
Oxy-acetylene flame ≈ 3000 °C.
Oxy-acetylene flame ≈ 3000 °C.
Q13. Marsh gas is: Practice
Correct answer: (A)
From anaerobic decay of organic matter in marshes.
From anaerobic decay of organic matter in marshes.
Q14. The first fully synthetic fibre was: Practice
Correct answer: (D)
Rayon is semi-synthetic (from cellulose).
Rayon is semi-synthetic (from cellulose).
Q15. Bakelite is a: Practice
Correct answer: (B)
Once set it does not soften on heating — switches, handles.
Once set it does not soften on heating — switches, handles.
Q16. The best quality coal (highest carbon) is: Practice
Correct answer: (D)
Anthracite has over ~90% carbon.
Anthracite has over ~90% carbon.
Q17. Quality of petrol is measured by: Practice
Correct answer: (B)
Higher octane = less knocking.
Higher octane = less knocking.
Q18. Blindness from spurious liquor is caused by: Practice
Correct answer: (B)
Methanol forms formaldehyde/formic acid in the liver.
Methanol forms formaldehyde/formic acid in the liver.
Q19. Water gas is a mixture of: Practice
Correct answer: (A)
Producer gas = CO + N₂.
Producer gas = CO + N₂.
Q20. An alcohol reacting with a carboxylic acid forms an: Practice
Correct answer: (D)
Esterification; esters have sweet/fruity smells.
Esterification; esters have sweet/fruity smells.