Organic chemistry (paper 2)

What atoms do hydrocarbons contain?

What atoms do hydrocarbons contain?

Carbon and hydrogen atoms

What are alkanes?

• Simplest type of hydrocarbon

• Saturated compounds

What’s the formula for alkanes?

CnH2n+2

What’s the formula for methane?

CH4

What’s the formula for ethane?

C2H6

What’s the formula for propane?

C3H8

What’s the formula for butane?

C4H10

Describe the properties of shorter chained hydrocarbons

• Lower viscosity (low resistance/flows easily)

• lower boiling points

• More flammable

What are shorter chained hydrocarbons used for?

useful fuels

What’s complete combustion?

occurs when there’s plenty of oxygen

What are the waste products of complete combustion?

Co2 and water vapour

Why are short hydrocarbons used for fuels?

• Due to the amount of energy released when they combust completely

• They are flammable

What is crude oil?

its a mixture of lots of different hydrocarbons (most are alkanes)

How is crude oil formed?

• formed from the remains of marine animals or plankton that died millions of years ago

• with high temperature and pressure, remains turn to crude oil

• it’s drilled up from rocks

What is fractional distillation?

The separation of different compounds in crude oil

What is fractional distillation used for?

Separating hydrocarbons into fractions

What’s the process of fractional distillation?

1. Crude oil is heated until most is in gas form, gas enters the column

2. There’s a temperature gradient (hot at bottom, cold as gas reaches the top)

3. Longer hydrocarbons have high boiling points, they condense and drain out, shorter hydrocarbons have lower boiling points, they condense at the top

4. You end with crude oil separated into different fractions, each with the same number of carbon atoms (similar boiling points)

What is cracking?

The splitting up of long chain hydrocarbons

Why do we use cracking?

To spilt long chain hydrocarbons into short chains to be used as useful fuels

What are alkenes used for?

Used as starting material, and used to make polymers

What type of reaction is cracking?

A thermal decomposition reaction (breaking molecules down by heating them)

What are the steps of cracking?

1. Heat long chain hydrocarbons to vaporise them (turn them into gas)

2. Vapour is passed over hot aluminium oxide catalyst

3. Long chain molecules split apart

What’s steam cracking?

Vaporise hydrocarbons, mix them with steam and then heat them at a very high temperature

What are alkenes?

They are unsaturated compounds

What type of bond do alkenes have?

Double bonds

What does a double bond mean?

Alkenes have two fewer hydrogens compared with alkanes

What are the first 4 alkenes?

1. Ethene

2. Propene

3. Butene

4. Pentene

What’s the formula for alkenes?

CnH2n

What’s incomplete combustion?

when there isn’t enough oxygen in the air

What are the waste products for incomplete combustion?

Carbon and carbon monoxide can be produced (poisonous gas) as well as arson dioxide and water vapour

What is the test for an alkene?

Bromine water

What happens when bromine water is in the presence of an alkene?

Bromine will go from orange to colourless

Why do the boiling point of longer chained hydrocarbons increase?

Because they have strong intermolecular forces