Topic 7 Organic chemistry
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: What are hydrocarbons?
Compounds made of only carbon and hydrogen atoms.
Q: What is an alkane?
A: A saturated hydrocarbon with single bonds. General formula: CₙH₂ₙ₊₂.
Q: What is an alkene?
A: An unsaturated hydrocarbon with a double bond. General formula: CₙH₂ₙ.
Q: How can you test for alkenes?
A: Bromine water turns from orange to colourless in an addition reaction.
Q: What happens in complete combustion of a hydrocarbon?
A: Hydrocarbon + O₂ → CO₂ + H₂O
Q: What is fractional distillation?
A: Separating crude oil into fractions based on boiling point.
Q: How do short-chain hydrocarbons differ from long-chain ones?
A: Shorter chains have lower boiling points, are more flammable, and less viscous.
: What is addition polymerisation?
A: Joining many alkene monomers to make a polymer. Example: Ethene → Polyethene.
Q: Difference between alkanes and alkenes?
A: Alkanes are saturated, less reactive. Alkenes are unsaturated, more reactive.
Q: Name 3 uses of crude oil fractions. .
A: Petrol, diesel, kerosene, bitumen.
What is crude oil?
Its a mixture of hydrocarbons
What is fractional distillation used for?
A: Separating crude oil into useful fractions based on boiling points.
Why do fractions separate in the fractionating column?
: Because hydrocarbons have different boiling points.
Why do shorter hydrocarbons have lower boiling points?
They have weaker intermolecular forces
What is complete combustion?
Burning hydrocarbons in plenty of oxygen to produce CO₂ and H₂O.
Q: What is incomplete combustion?
Burning hydrocarbons with limited oxygen, producing CO or carbon (soot).
Why is carbon monoxide dangerous?
It is toxic and reduces oxygen transport in the blood.
What is cracking?
A: Breaking long-chain hydrocarbons into shorter alkanes and alkenes.
Why is cracking done?
: To produce more useful short-chain fuels and alkenes.
: What conditions are needed for cracking?
High temperature and a catalyst (silica/alumina).
What is a monomer?
A small molecule that joins to form a polymer.
What is a polymer?
A long chain of repeating monomers
What is addition polymerisation?
Many alkene monomers join together to form a polymer.
: Why is it called addition polymerisation?
Because monomers add together with no other product formed.