Chemistry : C7

What is a hydrocarbon?

A covalent compound made up of only carbon and hydrogen atoms

What are alkanes, what are their bonds, how are they identified, what is their formula?

Alkanes

Single covalente bonds

Ends in -Ane

CnH2n + 2 =4 N for every carbon there are double hydrogens and 2 extra

What are alkenes, what are their bonds, how are they identified, what is their formula?

Alkenes

Joined by a double covalent bond

Ends in -ene

CnH2n = for every carbon there are double hydrogens

How are single bonds shown?

C - C

How are double bonds shown?

C = C

What are the first 4 alkanes?

1. Methane

2. Ethane

3. Propane

4. Butane

5. Pentane

6. Hexane (shape names from now on…)

What are the first 4 alkenes?

1. Ethene

2. Propene

3. Butene

4. Pentene

5. Hexene (shape names from now on..)

What is complete combustion?

Burning with a good supply of oxygen - burning to a blue flame

What us incomplete combustion?

Burning with a limited supply of oxygen. IT will burn at an orange flame.

What is the formula for combustion?

Hydrocarbon + oxygen = carbon dioxide + water

Define crude oil

Oil found in the ground formed from partially decayed plants and animals, under mud, millions of years ago.

It is a non-renewable fossil fuel.

What are the uses of crude oil?

• diesel oil

• Kerosene

• Petroleum

• Power stations

• Polymers

• Lubricants

• Solvents

• Detergents

What are the properties of smaller hydrocarbons?

• more runny (less viscous)

• Have lower boiling points

• Very flammable

What are the properties of longer hydrocarbons?

• less runny (more viscous)

• Higher boiling points (due to more bonds)

• Less flammable

Name each type of crude oil from smallest to longest hydrocarbon

Define fractional distillation

Separates fractions which contain hydrocarbons of different lengths. This is because each fraction has a different boiling point

Define cracking

The breaking down of long hydrocarbon chains into smaller useful alkanes and alkenes, a thermal decomposition process

How does fractional distillation occur?

1. Crude oil is extracted from oil fields below the ground

2. It is heated in a fractionating tower

3. The liquid evaporates and the vapour condenses at different temperatures

4. The light fractions have lower boiling points and come out first

5. The fraction with the lowest boiling point exits the tower

6. The fraction with the lowest boiling point comes at the bottom of the tower

7. This process produces a range of useful oils and fuels

What is the formula for cracking?

Long chain alkane = shorter alkane + alkene

Make sure carbon atoms are equal

Define saturated and unsatured

Saturated = all single bonds = alkanes

Unsaturated = all double bonds = alkenes

How do you test for alkenes?

Place orange bromine water into an ‘alkene’ solution and if present the solution will turn colourless

What are the 2 types of cracking?

Catalyst cracking

Steam cracking

How do you carry out catalyst cracking?

Heat the molecule at a high temperature (400 degrees) until it vaporises

Combine the vapour with aluminum oxide catalyst (pass over it)

Hydrocarbons split into smaller useful alkanes molecules on the surface of the catalyst

How do you carry out steam cracking?

Heat the molecule at a high temperature (400 degrees) until it vaporises

Hydrocarbon vapor is mixed with steam and heated to a high temperature

The heating splits the bonds and the molecules split