GCSE Chemistry- Hydrocarbons

What is crude oil?

A complex mixture of different compounds, many of which are known as hydrocarbons.

Is crude oil a renewable resource?

No, it is finite.

Where is crude oil found?

In rocks

Hydrocarbons

Compounds which only contain the elements carbon and hydrogen

How can compounds be extracted from crude oil and why is this?

They can be extracted using fractional distillation, because the individual compounds are not chemically bonded.

Formula for methane

CH4

Formula for Ethane

C2H6

Formula for Propane

C3H8

Formula for Butane

C4H10

General formula for Alkanes

C(n)H(2n+2)

Flammability

How easily a fuel ignites

Why are shorter chain hydrocarbons easier to ignite?

Because they have lower boiling points

Viscosity

How easily a liquid flows

Are shorter or longer chain hydrocarbons more viscous?

Longer chain hydrocarbons

Fractional distillation

A way of separating crude oil into individual compounds

In fractional distillation, what type of hydrocarbons are collected at the top of the column?

shorter chain hydrocarbons

Properties of shorter chain fuels

low boiling points, low viscosity, high flammability

What happens to temperature as you go up a fractional distillation column?

decreases

Step 1- Fractional distillation

Crude oil is heated to 350C until most of the hydrocarbons evaporate and turn into gases

Step 2- Fractional Distillation

Evaporated crude oil enters the fractionating column

Step 3- Fractional Distillation

The vapours cool as they rise up the column

Step 4- Fractional Distillation

When a substance reaches the height in the column where the temperature is equal to its boiling point, it condenses into a liquid.

Step 5- Fractional Distillation

The condensed liquid can then be collected and used.

What are any hydrocarbons that remain liquid after heating removed as?

Bitumen

Uses of Gas

Heating and cooking

Uses of Petrol

Fuel for cars

Uses of Kerosene

Fuel for aircrafts

Uses of Diesel Oil

Fuel for cars and trains

Uses of fuel oil

Fuel for ships

Uses of Bitumen

Roof and road surfacing

Cracking

The splitting up of long-chain hydrocarbons into smaller (alkene) molecules

What do hydrocarbons undergo when cracked?

Thermal decomposition

What can alkene molecules be used to make?

Polymers

How does cracking work?

Vapourised hydrocarbons are passed over a powdered catalyst at high temperature and pressure.

What does the catalyst do to the breakdown of hydrocarbons in cracking?

Speeds it up

What type of bonds do alkanes have?

Single bonds (saturated)

What type of bonds do alkenes have?

Double bonds (unsaturated)

Formula of Ethene

C2H4

Formula of Propene

C3H6

Formula of But-1-ene

C4H8

Formula of But-2-ene

C4H8

General formula for Alkenes

C(n)H(2n)

What do alkenes do in combustion?

React with oxygen in incomplete combustion giving smoky flames

Formula for incomplete combustion

Alkene + Oxygen → Carbon Monoxide + Water

Formula for complete combustion

Alkene + Oxygen → Carbon Dioxide + Water

Formula for a bromine water reaction

Alkene + Bromine → Dibromoalkane

What colour is bromine?

Brown

What colour is Dibromoalkane?

Colourless

What happens in a bromine water reaction?

When bromine water is added to an alkene and the bromine reacts with the double bond, decolourising the bromine water.

What is the bromine water reaction used to do?

Distinguish between an alkane and an alkene

What colour is bromine water when added to an alkene?

Colourless

What colour is bromine water when added to an alkane?

Remains Orange

Formula of reaction for alkane formation

Alkene + Hydrogen → Alkane

Formula for alcohol formation

Alkene + Water → Alcohol

Step 1- Bromine water reaction

Add 5 drops of Bromine water to both test tubes and place the stoppers

Step 2- Bromine water reaction

Open the stopper on the first test tube and add five drops of cyclohexane

Step 3- Bromine water reaction

Open the stopper on the second test tube and add 5 drops of cyclohexene

Safety Precautions- Bromine Water Reaction

Cyclohexane can be fatal if swallowed

Polymers

Substances of high molecular mass made up of small repeating units called monomers

What is needed for polymer formation?

Pressure and Catalyst

Properties of HDPE

Flexible, strong, shatter resistant, chemical resistant

Properties of LDPE

flexible, unreactive, can be made into films

Uses of HDPE

plastic bottles, pipes, buckets

Uses of LDPE

most carrier bags, bubble wrap

What is the structure of LDPE like?

Randomly arranged branched molecules

What is the structure of HDPE like?

Lined up molecules, no branching

Explain why HDPE has a higher density than LDPE

HDPE’s polymer chains are closer together, and there are more atoms per unit volume, increasing density.

What do thermosoftening plastics do when melted?

Melt

Why do thermosoftening plastics melt when heated?

Because they have weak intermolecular forces between neighbouring polymer molecules, so the forces require little energy to break.

What do thermosetting plastics do when heated?

Remain intact

Why do thermosetting plastics stay intact when heated?

Because there are covalent bonds holding neighbouring polymers together, which require a lot of energy to overcome.