Objectives:

To revise fractional distillation.

To explain why large hydrocarbons are cracked.

Outcomes:

All of you will be able to explain what is meant by fractional distillation.

Most of you will be able to explain why cracking is carried out.

Some of you will be able to recognise an alkene from a structural or molecular formulae.

Revision – Fractional Distillation 13.09.10

Starter:

List all the fuels you think you have used so far today and how you have used them e.g.

1) Gas – cooking breakfast.

Crude oil

Where is it found?

What is it used for?

What is it?

What is it made up of?

Fuel gas PetrolNaphtha KerosineDiesel Fuel Oil and bitumen

Small molecules

Medium molecules

Big molecules

Fuel gas Burned in the refinery to fuel the distillation process, sold as LPG, purified and sold as bottled camping gas.

Petrol/ gasoline.

Fuel for cars and motorcycles, also used to make chemicals.

Naphtha Used to make chemicals.

Paraffin/ Kerosine

Fuel for greenhouse heaters and jet engines, manufacture of chemicals.

Diesel Fuel Fuel for lorries, trains.

Fuel/ Lubricating oil

Fuel for the heating systems of large buildings, fuel for ships, lubricating oil.

Bitumen Roofing, and road surfaces.

Fractional distillationCrude oil can be separated by fractional distillation. The oil is evaporated and the hydrocarbon chains of different lengths condense at different temperatures:

Fractions with low boiling

points condense at

the top

Fractions with high boiling

points condense at the bottom

Long chain molecules. Short chain molecules

Does not flow very well as they are very thick.

Flows easily (they are quite thin).

They are less flammable (do not set on fire).

Are flammable (will set on fire).

Less volatile (does not turn into a gas).

Quite volatile (will evaporate).

Have a high boiling point. Have Low boiling points.

Butane

Ethane

Ethane

For example, this bond can be

“cracked” to give two of these:

Butane

For example, this bond can be

“cracked” to give two of these:

Ethane

Ethane

CrackingShorter chain hydrocarbons are in greater demand because they burn easier. They can be made from long chain hydrocarbons by “cracking”:

Making Hydrocarbons.

1) Decane C10H22

2) Butane C4H10

3) Pentane C5H12

4) Ethane C2H6

5) Propene C3H6.

6) Ethene C2H4.

Which is a correct statement about crude oil?

A. A mixture of carbohydrates.

B. Formed by the decay of dead sea creatures.

C. Consist of a mixture of very large molecules.

D. Is purified in an oil rig.

Which is a correct statement about fractionaldistillation?

A. Oil is separated into fractions with the same size molecule.

B. Oil is separated into fractions with the same density.

C. Oil is separated into fractions with similar size molecules.

D. Oil is separated into alkanes and alkenes.

Which is a correct order for these fractions working down from the top of the column?

A. Fuel gas, kerosine, petrol, diesel, bitumen.

B. Fuel gas, diesel, kerosine, petrol, bitumen.

C. Fuel gas, petrol, diesel, kerosine, bitumen.

D. Fuel gas, petrol, kerosine, diesel, bitumen.

Which of these is a true statement about the changes that occur as hydrocarbon molecules get larger?

A.Boiling point decreases.

B.Viscosity increases.

C.Flammability increases.

D.Transparency increases.

Which of these is an alkane?

A. C6H14

B. C4H8

C. C12H24

D. C102H204

Which of these is a true statement aboutalkenes?

A. They turn bromine water from colourless to red

B. They contain a double bond

C. The smallest alkene has 1 carbon atom

D. They have names that end in “ane.”