AQA GCSE Combined Science Chemistry- organic chemistry

paper 2

What is organic chemistry?

The study of carbon-containing compounds.

What is a hydrocarbon?

A compound made up of hydrogen and carbon atoms only.

What are alkanes?

Saturated hydrocarbons – they contain only single bonds.

What is the general formula for alkanes?

CₙH₂ₙ₊₂

Name the first four alkanes.

Methane, ethane, propane, butane.

What is a saturated compound?

One where all the carbon-carbon bonds are single.

What happens in complete combustion of a hydrocarbon?

Hydrocarbon + Oxygen → Carbon dioxide + Water

Why are hydrocarbons good fuels?

They release a lot of energy when combusted.

What is crude oil?

A mixture of different hydrocarbons found in the Earth’s crust.

How is crude oil separated?

By fractional distillation.

How does fractional distillation work?

Crude oil is heated → vapours rise → fractions condense at different temperatures.

What is a fraction in crude oil?

A group of hydrocarbons with similar boiling points and chain lengths.

Which hydrocarbons condense at the top of the fractionating column?

Short-chain hydrocarbons with low boiling points.

Which hydrocarbons condense at the bottom of the column?

Long-chain hydrocarbons with high boiling points.

What are short-chain hydrocarbons like?

More flammable, lower boiling point, runnier (less viscous).

What are long-chain hydrocarbons like?

Less flammable, higher boiling point, thicker (more viscous).

Why are short-chain hydrocarbons more useful as fuels?

They ignite more easily and burn cleaner.

What is cracking?

Breaking down long-chain hydrocarbons into shorter, more useful ones.

What are the products of cracking?

A shorter alkane and an alkene.

Why is cracking important?

It produces more useful fuels and alkenes for making plastics.

What are alkenes?

Unsaturated hydrocarbons – contain at least one C=C double bond.

What is the general formula for alkenes?

CₙH₂ₙ

How do you test for alkenes?

Add bromine water – it goes from orange to colourless.