Edexcel iGCSE Chemistry - Topic 4b Crude oil

Crude oil

A mixture of hydrocarbons made from the remains of organisms that died millions of years ago

Mixture

A substance consisting of two or more different elements or compounds not chemically combined

Hydrocarbon

A molecule made of hydrogen and carbon atoms only

Fractional distillation

A method of separating different liquids from a mixture of liquids, especially useful in separating crude oil.

What is similar among molecules in each fraction

Similar properties and boiling points

What is the relationship between boiling point and size of the molecule

As the size increases, so does the boiling point

What do most fractions mainly contain

Alkanes

Where is fractional distillation carried out

Fractionating column

Where is a fractionating column hot and cold

Hot at the bottom, cold at the top

What enters the fractionating column, and where? What happens?

Crude oil enters at the bottom, where it is very hot, so vapours rise

What happens to vapours of hydrocarbons with high boiling points

They condense and are tapped off first

What happens to the vapours of hydrocarbons with low boiling points

They condense and are tapped off higher up (lower temperatures), or leave at the top as a gas

Viscosity

The ease of flow of a liquid - high viscocity liquids are thick and flow less easily

What is the relationship between viscosity and length of a hydrocarbon chain

As the hydrocarbon chain increases in length, the attraction between hydrocarbon molecules also increase, which results in the liquid becoming more viscous

Volatility

The tendency of a substance to vaporise

What is the relationship between volatility and molecular size and why

As molecular size increases, hydrocarbon liquids become less volatile, because attraction between the molecules increases with increasing molecular size.

What is the relationship between melting/boiling point and the size of fractions

As size increases, so does melting/boiling point

Why do larger fractions have higher melting/boiling points?

As molecules get larger, the intermolecular forces become greater so more heat is needed to seperate the molecules.

What is the relationship between viscosity, carbon chain length and colour of fractions?

As the carbon chain length increases, the colour gets darker and it is more viscous

Uses of refinery gas (2)

Domestic heating, portable energy sources

Uses of petrol

Car fuel

Uses of naphtha

Chemical feedstock, cracked to make petrol

Uses of kerosene

aircraft fuel

Uses of diesel oil

Fuel for larger trucks

Uses of fuel oil

power stations and ships

What is coal used for (2)

To power fuel power stations and in steel production

What colour does cobalt chloride turn in the presence of water

From blue to pink

What gasses does the burning of fossil fuels release

Carbon dioxide, carbon monoxide, nitrogen oxides, sulphur oxides and water

Fuel

A substance which releases energy in an exothermic reaction

What product are formed when a hydrocarbon fuel is burned

Water and carbon dioxide

What is used as a catalyst in cracking? (2)

silica or alumina

What temperature is cracking performed at?

600-700 degrees C