Chemistry
🔒 Log in to trackCarbon compounds, fuels, polymers, industry and pollution
🔒 Log in to trackCarbon and its compounds
- Carbon forms long chains and rings (catenation) and has valency 4 (tetravalency).
- Allotropes: diamond (hardest, bad conductor, each C bonded to 4), graphite (soft, layered, conducts electricity — pencil 'lead', lubricant, electrodes), fullerene (C₆₀ buckminsterfullerene), graphene (single layer of graphite).
- Hydrocarbons: alkanes single bonds (CₙH₂ₙ₊₂, saturated), alkenes double bond (CₙH₂ₙ), alkynes triple bond (CₙH₂ₙ₋₂).
- Methanol is poisonous (can cause blindness); ethanol is the alcohol in drinks and is blended with petrol. Vinegar is about 5–8% acetic acid. Esters have a fruity smell.
- Soap = sodium or potassium salt of long-chain fatty acids, made by saponification (fat + NaOH). Soap forms scum in hard water; detergents work in hard water too.
- Hydrogenation of vegetable oil with a nickel catalyst gives vanaspati ghee.
Fuels
| Fuel | Main component |
|---|---|
| CNG | Methane |
| LPG | Butane (with propane); ethyl mercaptan is added for smell to detect leaks |
| Biogas / gobar gas | Methane (plus CO₂) |
| Oxy-acetylene flame | Acetylene (ethyne) — welding and cutting |
| Water gas | CO + H₂ |
| Producer gas | CO + N₂ |
- Hydrogen has the highest calorific value by mass. Octane number rates petrol; cetane number rates diesel.
- Coal by carbon content: anthracite > bituminous > lignite > peat.
- Ethylene (ethene) is used for artificial ripening of fruits (calcium carbide, which releases acetylene, is banned for this).
Polymers
| Polymer | Monomer / note |
|---|---|
| Polythene | Ethene |
| PVC | Vinyl chloride — pipes |
| Teflon | Tetrafluoroethylene — non-stick cookware |
| Bakelite | Phenol + formaldehyde — thermosetting, electrical switches |
| Nylon | First fully synthetic fibre |
| Natural rubber | Isoprene (polyisoprene) |
| Rayon | 'Artificial silk' from cellulose |
| Melamine | Thermosetting — crockery |
- Vulcanisation — heating rubber with sulphur (Charles Goodyear) to make it hard and elastic.
- Thermoplastics (polythene, PVC) soften on heating; thermosetting plastics (Bakelite, melamine) do not.
Industrial processes
| Process | Product | Catalyst |
|---|---|---|
| Haber | Ammonia | Iron |
| Contact | Sulphuric acid | Vanadium pentoxide (V₂O₅) |
| Ostwald | Nitric acid | Platinum |
| Solvay | Sodium carbonate | — |
| Chlor-alkali | NaOH, Cl₂, H₂ (electrolysis of brine) | — |
- Glass = silica (sand) + sodium carbonate + limestone, fused; borosilicate (Pyrex) resists heat; cobalt oxide gives blue glass.
- Portland cement (Joseph Aspdin); gypsum is added to slow its setting.
Pollution and poisons
| Substance | Effect |
|---|---|
| SO₂, NO₂ | Acid rain (damage to the Taj Mahal — 'marble cancer') |
| CFCs | Ozone layer depletion |
| CO₂, CH₄, N₂O, water vapour | Greenhouse effect |
| Carbon monoxide | Binds haemoglobin (carboxyhaemoglobin) — suffocation |
| Methyl isocyanate (MIC) | Bhopal gas tragedy, 1984 |
| Mercury | Minamata disease (Japan) |
| Cadmium | Itai-itai disease (Japan) |
| Arsenic | Black-foot disease; groundwater contamination |
| Excess fluoride | Fluorosis (teeth and bones) |
| Nitrate in water | Blue baby syndrome |
| Lead | Plumbism (lead poisoning) |
Detailed notes
Carbon — the backbone chemical
Carbon bonds to itself in long chains and rings (catenation) and always shows valency 4 (tetravalency) — together these give it millions of compounds, the field of organic chemistry. Its allotropes: diamond (hardest natural substance, does not conduct, each C bonded to 4 others), graphite (soft, slippery, conducts electricity — pencil 'lead', electrodes, lubricant), fullerene (C₆₀) and graphene (one-atom-thick sheet). Hydrocarbons: alkanes — single bonds, saturated, CₙH₂ₙ₊₂ (methane CH₄, ethane); alkenes — one double bond, CₙH₂ₙ (ethene); alkynes — one triple bond, CₙH₂ₙ₋₂ (ethyne = acetylene).
Fuels — what burns in what
| Fuel | Main component |
|---|---|
| CNG | Methane |
| LPG | Butane (+ propane); ethyl mercaptan added for smell |
| Biogas (gobar gas) | Methane (+ CO₂) |
| Oxy-acetylene flame | Ethyne (acetylene) — welding/cutting (~3000 °C) |
| Water gas | CO + H₂ |
| Producer gas | CO + N₂ |
| Coal grades rise with carbon: peat → lignite → bituminous → anthracite (best). Petroleum ('black gold') is separated by fractional distillation into refinery gas, petrol, naphtha, kerosene, diesel, lubricating oil and bitumen (road tar, residue). |
Everyday carbon compounds
- Methanol (wood spirit) is poisonous — even small doses cause blindness; ethanol is drinkable alcohol, blended into petrol.
- Vinegar = 5–8% acetic acid. Esters (acid + alcohol) give fruits their smell.
- Soap = sodium/potassium salt of a long-chain fatty acid, made by saponification (fat + NaOH). In hard water soap forms useless scum; detergents work even in hard water.
- Hydrogenation: vegetable oil + H₂ with a nickel catalyst → vanaspati ghee (solid fat).
Industrial processes — name ↔ product
| Process | Product |
|---|---|
| Haber | Ammonia (N₂ + 3H₂, iron catalyst) |
| Contact | Sulphuric acid (V₂O₅ catalyst) |
| Ostwald | Nitric acid (from ammonia, Pt catalyst) |
| Solvay | Sodium carbonate (washing soda) |
| Bosch | Hydrogen (from water gas) |
Polymers and fibres
Polymers are giant molecules of repeating units. Natural: cotton (cellulose), silk and wool (proteins), starch, natural rubber. Vulcanisation (Charles Goodyear, 1839) heats rubber with sulphur — tyres get strength and elasticity. Synthetic: polythene (from ethene — bags), PVC (pipes, insulation), Teflon/PTFE (non-stick pans), nylon (first fully synthetic fibre, 1935 — ropes, parachutes), bakelite (first plastic, hard, thermosetting — switch boards), rayon ('artificial silk', made from wood cellulose).
Pollution — pollutant ↔ effect
- Carbon monoxide (CO) binds haemoglobin ~200 times more strongly than O₂ → suffocation deaths from geysers and coal stoves.
- SO₂ and NOₓ → acid rain; SO₂ was the killer of the London smog (1952).
- Mercury → Minamata disease; cadmium → itai-itai disease (both Japan, 1950s–60s).
- CFCs (old fridge/aerosol gases) ate the ozone layer — phased out by the Montreal Protocol (1987); the ozone layer lies in the stratosphere.
- Greenhouse gases (CO₂, CH₄, water vapour) drive global warming; the Kyoto Protocol (1997) and Paris Agreement (2015) target emissions. The Bhopal gas tragedy (1984) was methyl isocyanate (MIC).
Quick revision
- CNG/biogas–methane; LPG–butane (smelly ethyl mercaptan); welding–acetylene; anthracite–best coal.
- Haber–NH₃, Contact–H₂SO₄, Ostwald–HNO₃, Solvay–Na₂CO₃.
- Nylon first synthetic fibre; bakelite first plastic; vulcanisation = rubber + sulphur; Teflon non-stick.
- Methanol poison, ethanol safe-ish; soap scums in hard water, detergent does not; hydrogenation uses nickel.
- CO–haemoglobin poison; Minamata–Hg; itai-itai–Cd; CFC–ozone (Montreal 1987); Bhopal–MIC 1984.
Types of questions asked
Every way this subtopic shows up in exams — how to recognise it, the formula or logic to use, and a solved example.
Type 1: Fuel ↔ main componentvery common3 practice Q
'CNG is mainly…', 'LPG contains…', 'why does LPG smell', 'which gas is used in welding', 'best variety of coal'.
- Gas family: CNG and biogas = methane; LPG = butane (+ propane); welding = acetylene (ethyne) with oxygen.
- LPG leaks are smellable because ethyl mercaptan is added — the gas itself is odourless.
- Coal ranking by carbon: peat < lignite < bituminous < anthracite; petroleum splits by fractional distillation (bitumen last). Why: each fuel is a named hydrocarbon, so the answer is recall plus the one-line use.
Example: The gas used with oxygen in a welding torch is —
Acetylene (ethyne) — its oxy-acetylene flame reaches about 3000 °C and cuts steel.
Type 2: Industrial process ↔ productvery common3 practice Q
'Haber process gives…', 'sulphuric acid is made by the … process', 'Ostwald process produces…', match-the-column of processes and chemicals.
- Fix the four: Haber → ammonia; Contact → sulphuric acid; Ostwald → nitric acid; Solvay → sodium carbonate.
- Catalyst tags: Haber–iron, Contact–V₂O₅, Ostwald–platinum.
- In match-the-columns, anchor on ammonia (Haber) — the rest fall into place by elimination.
Example: The Contact process manufactures —
Sulphuric acid (H₂SO₄) — SO₂ is oxidised to SO₃ over a V₂O₅ catalyst, then absorbed in water.
Type 3: Polymers, plastics and fibresvery common3 practice Q
'First synthetic fibre / first plastic', 'Teflon is used for…', 'vulcanisation of rubber is done with…', 'rayon is called artificial…', natural vs synthetic classification.
- Records: nylon = first fully synthetic fibre; bakelite = first plastic (thermosetting); rayon = artificial silk from cellulose.
- Uses: polythene–bags, PVC–pipes, Teflon–non-stick, nylon–ropes and parachutes.
- Vulcanisation = natural rubber + sulphur (Goodyear) → tyres.
- Natural fibres: cotton–cellulose; silk/wool–protein; synthetic: nylon, polyester, acrylic.
Example: Vulcanised rubber is made by heating natural rubber with —
Sulphur — cross-links form between chains, making the rubber strong, elastic and heat-resistant (tyres).
Type 4: Allotropes and hydrocarbon familiescommon3 practice Q
'Which allotrope of carbon conducts electricity', 'hardest natural substance', 'alkane/alkene/alkyne general formula', 'which hydrocarbon is saturated'.
- Allotropes: diamond (hardest, non-conductor), graphite (soft, conducts), fullerene C₆₀, graphene.
- Families: alkane CₙH₂ₙ₊₂ (single bonds, saturated); alkene CₙH₂ₙ (double); alkyne CₙH₂ₙ₋₂ (triple).
- Methane (CH₄) is the simplest alkane and the main gas in CNG/biogas.
Example: Which general formula belongs to an alkyne?
CₙH₂ₙ₋₂ — the triple bond (as in acetylene, C₂H₂) leaves fewer hydrogens than an alkene.
Type 5: Everyday carbon chemistrycommon3 practice Q
'Which alcohol causes blindness', 'vinegar contains…', 'why does soap fail in hard water', 'hydrogenation of oils uses which catalyst', 'esters give…'.
- Alcohols: methanol = poison (blindness, death); ethanol = the alcohol in drinks and petrol blends.
- Vinegar = 5–8% acetic acid; esters (acid + alcohol) = fruity smells.
- Soap = fatty-acid salt made by saponification; forms scum with hard-water Ca²⁺/Mg²⁺ — detergents do not.
- Hydrogenation of vegetable oil uses a nickel catalyst → vanaspati.
Example: Soap does not lather well in hard water because —
Ca²⁺/Mg²⁺ ions react with soap to form insoluble scum; synthetic detergents are made to work even so.
Type 6: Pollutant ↔ disease or eventcommon3 practice Q
'Minamata disease is caused by…', 'which gas causes acid rain', 'CFCs damage…', 'Bhopal gas tragedy leaked…', 'why is CO poisonous'.
- Japanese diseases: Minamata–mercury; itai-itai–cadmium.
- CO binds haemoglobin far more strongly than oxygen → carbon monoxide poisoning.
- SO₂ + NOₓ → acid rain; CFCs → ozone-hole (Montreal Protocol 1987); Bhopal 1984 leaked methyl isocyanate (MIC).
- Greenhouse gases: CO₂, CH₄ — Kyoto 1997, Paris 2015.
Example: Minamata disease resulted from poisoning by —
Mercury — factory effluent in Japan entered fish, and fish-eating villagers were poisoned. (Cadmium caused itai-itai.)
Formulas
iron catalyst
Shortcut tricks
⚡ Process → product: 'Haber-Ammonia, Contact-Sulphuric, Ostwald-Nitric, Solvay-Soda'
Pair the catalysts too: Haber — Fe, Contact — V₂O₅, Ostwald — Pt.
Example: Which catalyst is used in the Contact process?
Vanadium pentoxide (V₂O₅).
⚡ Japanese diseases: 'Mina-Mercury, Itai-Cadmium'
Minamata — Mercury; Itai-itai ('ouch-ouch', bone pain) — Cadmium.
Where students lose marks
Saying LPG is mainly methane — LPG is mainly butane; CNG and biogas are mainly methane.
Calling Bakelite a thermoplastic — it is thermosetting.
Naming phosgene for the Bhopal tragedy — the gas was methyl isocyanate.
Practice sets — 22 questions
Sets of 10, mixed across the question types above. Each answer comes with a step-by-step explanation.
Topic test · 10 questions
Suggested time 3 min · wrong answers go to your mistake notebook automatically.