Chemistry AQA GCSE Organic

Crude oil

A mixture of many different hydrocarbons, mainly alkanes.

How is crude oil formed?

-From the remains of ancient sea creatures (plankton)

-buried in mud and compressed

-over millions of years with heat and pressure, forming oil and gas.

What is crude oil used for?

-As a source of fuels

-and as feedstock to make plastics, solvents, detergents, etc.

Q: Why must crude oil be separated?

Because it contains different hydrocarbons with different boiling points — it’s not useful in its raw form.

How is crude oil separated?

A: By fractional distillation.

What property allows crude oil to be separated by fractional distillation?

Different hydrocarbons have different boiling points.

What happens during fractional distillation?

Crude oil is heated until it vaporises.

Vapour enters a fractionating column (hot at bottom, cooler at top).

Hydrocarbons condense at different heights depending on their boiling points.

Where do short-chain hydrocarbons condense?

Near the top of the column (low boiling points).

Where do long-chain hydrocarbons condense?

Near the bottom (high boiling points).

What are hydrocarbons?

Compounds made only of carbon and hydrogen atoms.

What are the two main types of hydrocarbons?

Alkanes (saturated) and alkenes (Unsaturated)

How does chain length affect properties?

Shorter chains: lower boiling points, more flammable, less viscous.

Longer chains: higher boiling points, less flammable, more viscous.

What is the general formula for alkanes?

Cn​H2n+2​

Are alkanes saturated or unsaturated?

Saturated – they contain only single covalent bonds.

What are the first four alkanes?

Methane (CH₄), Ethane (C₂H₆)

Propane (C₃H₈), Butane (C₄H₁₀)

Mad Ethan Picks Burger

How do alkanes burn in a good supply of oxygen?

Complete combustion – produces carbon dioxide and water.

What is incomplete combustion?

When there isn’t enough oxygen

Forms CO(Carbon monxide)/Soot(Carbon molecules)+H20

word equation for complete combustion of methane

Methane + Oxygen → Carbon dioxide + Water

Why is incomplete combustion dangerous?

Carbon monoxide is toxic

We cant see it or smell it