Organic Chemistry
What's covered
Key facts
The general formula for alkanes is CₙH₂ₙ₊₂.
Addition polymerisation is when many alkene monomers join to form a polymer.
Carbon monoxide is dangerous because it binds tightly to haemoglobin in red blood cells, blocking oxygen transport and causing potentially fatal poisoning.
Alkenes from cracking are used to make polymers.
Ethanol can be produced by the fermentation of glucose using yeast in the absence of oxygen (anaerobic respiration).
Alcohols are named with the suffix -ol; their functional group is –OH (e.g. methanol, ethanol).
In addition polymerisation, each monomer's double bond opens to form a new single bond joining monomers.
Equivalent written form: CnH(2n+2) / CₙH₂ₙ₊₂.
The test for an alkene is that bromine water decolorises (orange → colourless) as bromine adds across the C=C double bond.
Complete combustion of a hydrocarbon (with sufficient oxygen) produces carbon dioxide and water as the only products.
Sample questions
A taste of the 70 questions in this topic — answers marked. Sign up to practise the full set with spaced repetition.
What is the first alkane in the series?
- •Ethane (C₂H₆)
- •Ethene (C₂H₄)
- ✓Methane (CH₄)
- •Methanol (CH₃OH)
What is the test for an alkene?
- •Alkenes always burn with a smokier yellow flame than alkanes
- ✓Bromine water decolorises (orange → colourless) as it adds across C=C
- •Sodium added to the sample fizzes vigorously, releasing hydrogen
- •Universal indicator turns blue/purple because alkenes are slightly basic
What are the products of complete combustion of a hydrocarbon fuel?
- •Carbon and water
- •Carbon dioxide and hydrogen
- ✓Carbon dioxide and water
- •Carbon monoxide and water
What is cracking?
- ✓Breaking long alkanes into short alkanes and alkenes, matching supply to demand
- •Joining short alkanes into longer, higher-boiling fuels for industrial use
- •Removing sulfur from crude oil to reduce acid rain when fuel is burnt
- •Separating crude oil fractions by boiling point in a distillation column
What are the conditions needed for fermentation of glucose to produce ethanol?
- •Bacteria, aerobic at 100°C, neutral pH; gives ethanol + O₂
- •Concentrated H₂SO₄ catalyst, ~300°C, 70 atm; gives ethanol + steam
- •UV light, yeast catalyst, 60°C, sealed high-pressure vessel
- ✓Yeast, anaerobic conditions, ~37°C, neutral pH; gives ethanol + CO₂
What are the names of the first four alkanes in order of increasing carbon atoms?
- •Ethene, propene, butene, pentene (these are alkenes)
- ✓Methane (1C), ethane (2C), propane (3C), butane (4C)
- •Methanol, ethanol, propanol, butanol (these are alcohols)
- •Propane, methane, butane, ethane (correct alkanes, wrong order)
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