Chemistry

medium importance~1 Q in Tier 113 formulas⚡ 10 shortcuts5 subtopics

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Carbon compounds, fuels, polymers, industry and pollution

⏱ 5 min read🧩 6 question types🎯 22 practice Q

The idea in one minute

Carbon forms long chains, so it makes millions of compounds. This lesson covers carbon forms, fuels, polymers, factory processes and pollution. Nearly every question asks you to match a name to its product, use or effect.

Carbon and its forms

Carbon joins to itself in chains and rings. This is catenation. Its valency is 4, called tetravalency.

Allotropes are different forms of one element.

Diamond: hardest natural substance. It does not conduct.
Graphite: soft and slippery. It conducts electricity. It is used in pencils, electrodes and lubricants.
Fullerene (C₆₀): a ball of 60 carbon atoms.
Graphene: a single layer of graphite.

Hydrocarbons

Family	Bonds	General formula
Alkane	Single, saturated	$C_nH_{2n+2}$
Alkene	One double bond	$C_nH_{2n}$
Alkyne	One triple bond	$C_nH_{2n-2}$

Methane (CH₄) is the simplest alkane. Ethene is an alkene. Ethyne (acetylene, C₂H₂) is an alkyne.

Fuels

Fuel	Main component
CNG	Methane
LPG	Butane (with propane)
Biogas (gobar gas)	Methane, plus CO₂
Oxy-acetylene flame	Ethyne (acetylene), for welding and cutting
Water gas	CO + H₂
Producer gas	CO + N₂

LPG has no smell. Ethyl mercaptan is added so a leak can be smelt.
Hydrogen has the highest calorific value by mass.
Octane number rates petrol. Cetane number rates diesel.
Coal ranks by carbon: peat, lignite, bituminous, anthracite. Anthracite is best.
Fractional distillation splits petroleum into refinery gas, petrol, naphtha, kerosene, diesel, lubricating oil and bitumen.
Ethylene ripens fruit. Calcium carbide is banned for this.

Everyday carbon compounds

Methanol is poisonous. It can cause blindness. Ethanol is the alcohol in drinks and is blended with petrol.
Vinegar is about 5 to 8% acetic acid.
Esters give fruits their smell.
Soap is a sodium or potassium salt of a long-chain fatty acid. Saponification (fat + NaOH) makes it.
Soap forms scum in hard water. Detergents work in hard water too.
Hydrogenation of vegetable oil uses a nickel catalyst. It gives vanaspati ghee.

Watch: Methanol is poison. Ethanol is the drinking alcohol.

Polymers

A polymer is a giant molecule made of repeating units.

Polymer	Note
Polythene	From ethene; bags
PVC	From vinyl chloride; pipes
Teflon	From tetrafluoroethylene; non-stick cookware
Bakelite	Phenol + formaldehyde; first plastic; thermosetting; switches
Nylon	First fully synthetic fibre
Natural rubber	Polyisoprene
Rayon	Artificial silk from cellulose
Melamine	Thermosetting; crockery

Vulcanisation heats rubber with sulphur (Charles Goodyear). It makes rubber hard and elastic.
Thermoplastics (polythene, PVC) soften on heating. Thermosetting plastics (Bakelite, melamine) do not.

Factory processes

Process	Product	Catalyst
Haber	Ammonia	Iron
Contact	Sulphuric acid	Vanadium pentoxide (V₂O₅)
Ostwald	Nitric acid	Platinum
Solvay	Sodium carbonate	none
Chlor-alkali	NaOH, Cl₂ and H₂ from brine	none

Glass is silica (sand), sodium carbonate and limestone fused together. Borosilicate (Pyrex) resists heat. Portland cement was made by Joseph Aspdin. Gypsum is added to slow its setting.

Pollution and poisons

Substance	Effect
SO₂, NO₂	Acid rain; damage to the Taj Mahal
CFCs	Ozone layer depletion
CO₂, CH₄, N₂O, water vapour	Greenhouse effect
Carbon monoxide	Binds haemoglobin; suffocation
Methyl isocyanate (MIC)	Bhopal gas tragedy, 1984
Mercury	Minamata disease, Japan
Cadmium	Itai-itai disease, Japan
Arsenic	Black-foot disease; groundwater
Excess fluoride	Fluorosis of teeth and bones
Nitrate in water	Blue baby syndrome
Lead	Plumbism

Tip: Minamata starts with M, like Mercury. Itai-itai means ouch-ouch, and cadmium is the cause.

Question types you will see

Each type: how to recognise it, the method step by step, and one question to try.

Type 1very common3 practice Q

Fuel and main component

How to spot it:

The question says 'CNG is mainly', 'LPG contains', 'why does LPG smell', 'gas used in welding' or 'best coal'.

Method

CNG and biogas are methane.
LPG is butane with propane. Ethyl mercaptan gives it a smell.
Welding uses acetylene (ethyne) with oxygen.
Coal ranking: peat, lignite, bituminous, anthracite.

Why it works:

Each fuel is a named hydrocarbon, so the answer is recall plus one use.

Try this

Which gas is used with oxygen in a welding torch?

Show solution

The flame must be very hot.
The gas is ethyne.

Answer

Acetylene (ethyne)

Type 2very common3 practice Q

Industrial process and product

How to spot it:

The question says 'Haber process gives', 'sulphuric acid is made by', or gives a match-the-column of processes and chemicals.

Method

Fix four pairs: Haber-ammonia, Contact-sulphuric acid, Ostwald-nitric acid, Solvay-sodium carbonate.
Add catalysts: Haber iron, Contact V₂O₅, Ostwald platinum.
Anchor on ammonia and eliminate the rest.

Why it works:

Each process is named after its inventor or its method and is fixed.

Try this

The Contact process makes which chemical?

Show solution

SO₂ is oxidised to SO₃ over V₂O₅.
SO₃ is absorbed to make the acid.

Answer

Sulphuric acid (H₂SO₄)

Type 3very common3 practice Q

Polymers, plastics and fibres

How to spot it:

The question asks the first synthetic fibre, the first plastic, a use of Teflon, or what vulcanisation uses.

Method

Records: nylon is the first fully synthetic fibre. Bakelite is the first plastic.
Uses: polythene bags, PVC pipes, Teflon non-stick, nylon ropes and parachutes.
Vulcanisation is natural rubber with sulphur.
Cotton is cellulose. Silk and wool are protein.

Why it works:

Polymers are named for their monomer or their use, and exams test both.

Try this

Vulcanised rubber is made by heating natural rubber with what?

Show solution

Goodyear found the method.
The added element is sulphur.

Answer

Sulphur

Type 4common3 practice Q

Allotropes and hydrocarbon families

How to spot it:

The question asks which carbon form conducts, the hardest natural substance, a general formula, or which hydrocarbon is saturated.

Method

Diamond is hardest and does not conduct. Graphite conducts.
Alkane $C_nH_{2n+2}$ is saturated. Alkene $C_nH_{2n}$ . Alkyne $C_nH_{2n-2}$ .
Methane is the simplest alkane.

Why it works:

A double or triple bond takes the place of hydrogen atoms, so the formula loses hydrogens.

Try this

Which general formula belongs to an alkyne?

Show solution

An alkyne has a triple bond.
Acetylene C₂H₂ fits $C_nH_{2n-2}$ with n = 2.

Answer

$C_nH_{2n-2}$

Type 5common3 practice Q

Everyday carbon chemistry

How to spot it:

The question asks which alcohol causes blindness, what vinegar contains, why soap fails in hard water, or the catalyst for hydrogenation.

Method

Methanol is poison. Ethanol is drinkable.
Vinegar is 5 to 8% acetic acid.
Soap is made by saponification and forms scum in hard water.
Hydrogenation of oil uses nickel and gives vanaspati.

Why it works:

Each item links one chemical to one everyday fact.

Try this

Why does soap not lather well in hard water?

Show solution

Hard water has calcium and magnesium ions.
They react with soap to form insoluble scum.

Answer

Scum forms; detergents work even in hard water

Type 6common3 practice Q

Pollutant and disease or event

How to spot it:

The question says 'Minamata disease is caused by', 'which gas causes acid rain', 'CFCs damage', or 'Bhopal gas leaked'.

Method

Minamata: mercury. Itai-itai: cadmium.
CO binds haemoglobin far more strongly than oxygen.
SO₂ and NOₓ cause acid rain. CFCs harm the ozone layer (Montreal Protocol 1987).
Bhopal 1984 was methyl isocyanate. Greenhouse gases: CO₂, CH₄.

Why it works:

Each pollutant harms one target, and exams pair them.

Try this

Minamata disease resulted from poisoning by which metal?

Show solution

Factory waste in Japan entered fish.
The pollutant was mercury.

Answer

Mercury (cadmium caused itai-itai)

Formula sheet

Alkane / alkene / alkyne

C_nH_{2n+2},\quad C_nH_{2n},\quad C_nH_{2n-2}

Haber process

N_2 + 3H_2 \rightleftharpoons 2NH_3

iron catalyst

Complete combustion of methane

CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O

Shortcuts that save time

⚡ Process to product

Haber gives ammonia. Contact gives sulphuric acid. Ostwald gives nitric acid. Solvay gives soda. Catalysts: Haber Fe, Contact V₂O₅, Ostwald Pt.

Example

Which catalyst is used in the Contact process?

Show solution

The Contact process makes sulphuric acid.
Its catalyst is vanadium pentoxide.

Answer

V₂O₅

⚡ Japanese diseases

Minamata goes with mercury. Itai-itai (bone pain) goes with cadmium.

Mistakes to avoid

Where most students lose marks on this subtopic.

Mistake 01

Saying LPG is mainly methane.

LPG is mainly butane. CNG and biogas are mainly methane.

Mistake 02

Calling Bakelite a thermoplastic.

Bakelite is thermosetting.

Mistake 03

Naming phosgene for the Bhopal tragedy.

The gas was methyl isocyanate (MIC).

Mistake 04

Mixing up methanol and ethanol.

Methanol is poisonous. Ethanol is the drinking alcohol.

Mistake 05

Saying detergent forms scum in hard water.

Soap forms scum. Detergents work in hard water.

Quick revision

Read this the night before the exam.

CNG and biogas: methane. LPG: butane with ethyl mercaptan for smell. Welding: acetylene.
Anthracite is the best coal.
Haber: NH₃. Contact: H₂SO₄. Ostwald: HNO₃. Solvay: Na₂CO₃.
Nylon is the first synthetic fibre. Bakelite is the first plastic.
Vulcanisation is rubber plus sulphur. Teflon is non-stick.
Hydrogenation uses a nickel catalyst. Soap scums in hard water.
CO binds haemoglobin. Minamata: Hg. Itai-itai: Cd. CFC: ozone. Bhopal: MIC, 1984.

Practice: 22 questions

Sets of 10, mixed across the question types above. Every answer has a step-by-step explanation.

Topic test · 10 questions

Suggested time 3 min · wrong answers go to your mistake notebook automatically.

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