Topic C7-Organic chemistry

Question 1

What are hydrocarbons

Answer 1

They only contain hydrogen and carbon atoms

Question 2

What is the general formula for alkanes

Answer 2

Cn H2n+2

Question 3

What is the general formula for alkanes

Answer 3

Cn H2n

Question 4

What are alkanes

Answer 4

They are saturated compounds- each carbon atom forms for single covalent bonds

Question 5

What are the first 4 alkanes

Answer 5

Methane
ethane
propane
butane

Question 6

What are the properties of hydrocarbons

Answer 6

As the length of carbon chain changes the properties of hydrocarbons changes

1) The shorter the carbon chain, the more runny a hydrocarbon is- The less viscous (gloopy) it is
2) hydrocarbons with shorter carbon chains are also more volatile (lower boiling points)
3) The shorter the carbon chain the more flammable (easier to ignite) the hydrocarbon is
4) The properties of hydrocarbons affect what they used for

Question 7

What happens during combustion

Answer 7

Both carbon and hydrogen from the hydrocarbon are oxidised

Question 8

How is crude oil informed

Answer 8

1) It is formed from the remains of plants and animals mainly plankton that died millions of years ago and were buried in mud.over millions of years with high temperatures and pressures that turnes into crude oil which can be drilled up from the rocks where it is found
2) fossil feels like coal, oil and gas are called non-renewable fuels and they are finite

Question 9

What can be used to separate hydrocarbon fractions

Answer 9

Fractional distillation

Question 10

What is fractional distillation

Answer 10

As crude oil is a mixture of loads of different hydrocarbons most of which are alkanes the different compounds can be separated using this

Question 11

How does fractional distillation work

Answer 11

1) The oil is heated until most of it has turned into gas. Gas enter a fractionating column
2) in the column there is a temperature gradient meaning that it’s hot at the bottom and gets cooler as you go up
3) The larger hydrocarbons have higher boiling points. This condenses back into liquid and drains out of the column earlier on when it is near the bottom. The shorter hydrocarbons have lower boiling points they condense and drain out much later near to the top of the column where it is cooler
4) you end up with the crude oil mixture separated out into different fractions. Each fraction contains a mixture of hydrocarbons that will contain a similar number of carbon atoms

Question 12

What is the meaning of cracking

Answer 12

Splitting up of long chain hydrocarbons

Question 13

Why is cracking important

Answer 13

1) Short chain hydrocarbons of flammable so make good fuel and are in high demand however long chain hydrocarbons form thick gloopy liquids like tor which aren’t all that usefull.
2) so a lot of the longer alkanes molecules produced from fractional distillation are turned into smaller more useful ones by this process

Question 14

What else is produced due to cracking

Answer 14

Another type of hydrocarbons called Alkanes. alkanes are a lot more reactive than alkanes.

Question 15

What are different methods of cracking

Answer 15

Cracking is a thermal decomposition reaction meaning that molecules are broken down by heat

1) The first step is to heat long chain hydrocarbons to evaporate them
2) Then the vapor is passed over a hot powdered aluminium oxide catalyst
3) The long chain molecules split apart on the surface of the specs of catalyst this is called catalytic cracking