Fuels and Hydrocarbons

Question 1

What is a

hydrocarbon?

Answer 1

a compound containing only carbon and hydrogen

Question 2

What is

crude oil?

Answer 2

• a complex mixture of hydrocarbons
• containing molecules in which carbon atoms are in chains or rings
• an important source of useful substances
• a finite resource

Question 3

Describe

fractional distillation.

Answer 3

• crude oil is a mixture of hydrocarbons
• all hydrocarbons are evaporated
• the tower is hotter at the bottom and cooler at the top
• gaseous hydrocarbons enter tower at bottom and travel upwards
• different hydrocarbons have different boiling points
• hydrocarbons with fewer carbon atoms condense later and exit the column further up
• different fractions are separated on the basis of where they condensed
• refinery gases do not condense
• fractions are mixtures of hydrocarbons with similar chain length

Question 4

What are the uses of

gases

from crude oil?

Answer 4

domestic heating
cooking

Question 5

What is the use of

petrol

from crude oil?

Answer 5

fuel for cars

Question 6

What is the use of

kerosene

from crude oil?

Answer 6

fuel for aircraft

Question 7

What is the use of

diesel oil

from crude oil?

Answer 7

fuel for some cars and trains

Question 8

What is the use of

fuel oil

from crude oil?

Answer 8

fuel for large ships and in some power stations

Question 9

What is the use of

bitumen

from crude oil?

Answer 9

surface roads and roofs

Question 10

What are the trends in physical properties as hydrocarbon chain length increases and decreases?

Answer 10

As the size of the molecule increases, so do the melting and boiling points and the viscosity.
As chain length decreases however, so does volatility and flammability.

Question 11

What is a homologous series?

Answer 11

A series of compounds which have the same general formula, similar chemical properties, same functional group and trends in physical properties.

Question 12

What is the formula for the combustion of hydrocarbons?

Answer 12

hydrocarbon + oxygen -> carbon dioxide + water (+energy)

Question 13

When does incomplete combustion occur?

Answer 13

when there is not enough oxygen

Question 14

What is

cracking?

Answer 14

the breaking down of long chain alkanes into shorter, more useful, alkanes and alkenes

it is an example of thermal decomposition

Question 15

Monkeys?

Answer 15

Eat
Penguins
But
Penguins
Hide

Question 16

What is the general formula for alkanes?

Answer 16

CnH2n+2

Question 17

Why are alkanes saturated hydrocarbons?

Answer 17

because they contain only (C-C) single bonds

Question 18

What is the general formula for alkenes?

Answer 18

CnH2n

Question 19

Why are alkenes unsaturated?

Answer 19

Because they contain (C=C) double bonds

Question 20

How is bromine water used to distinguish between alkanes and alkenes?

Answer 20

If alkenes are present, the bromine water will be decolourised whereas there will be no change with alkanes.

Question 21

What is a polymer?

Answer 21

A substance of high average relative molecular mass made up of small repeating units.

Question 22

What is

polymerisation?

Answer 22

the reaction between many small molecules (monomers) joining up to make a polymer

Question 23

What are the properties and uses of

poly(ethene)?

‘polythene’

Answer 23

• flexible
• cheap
• can be made into thin films

carrier bags, shampoo bottles, food wrap

Question 24

What are the properties and uses of

poly(propene)?

‘polypropylene’

Answer 24

• flexible
• strong
• resists shattering

buckets, bowls, crates, ropes, carpets

Question 25

What are the properties and uses of

poly(chloroethene)?

‘PVC’

Answer 25

• tough
• electrical insulator
• can be made hard or flexible

insulation for electrical wires, windows, gutters, pipes

Question 26

What are the properties and uses of

poly(tetrafluoroethene)?

‘PFTE’

Answer 26

• slippery
• chemically unreactive

non-stick coatings for pans, containers for laboratory substances

Question 27

What are the positives and negatives of

recycling

as a plastic ‘solution’?

Answer 27

+the plastic is used again to make new products from old ones

-people have to sort their waste at home before putting it into bins
-it is expensive

Question 28

What are the positives and negatives of

biodegradable plastic

as a plastic ‘solution’?

Answer 28

+the plastic will be broken down by microbes and removed from the environment
+plastic shopping bags can be made out of this and will be broken down within a couple of months

Question 29

What are the positives and negatives of

landfill

as a plastic ‘solution’?

Answer 29

+it is the cheapest method of disposing plastics

-it uses lots of land that could be used for growing food
-the plastic will stay in the environment for many hundreds of years without being broken down

Question 30

What are some general characteristics of

polymers?

Answer 30

• different physical properties to the monomers they came from
• hydrophobic so often waterproof
• durable because they are unreactive

last a long time but break down very slowly

Question 31

What does catalytic cracking require?

Answer 31

• high temperatures of 600-700°C
• a catalyst of alumina or silica

alumina is aluminium oxide

Question 32

How is catalytic cracking carried out?

Answer 32

1. The alumina or silica catalyst is heated to 600-700°C.
2. The alkane is gently heated - causing it to vaporise.
3. The alkane vapour passes over the hot catalyst.
4. The catalyst allows the reaction to happen much quicker.
5. This produces shorter alkanes and alkenes.
6. The vapours are collected ‘over water’.