Crude oil and fuels

Question 1

What is crude oil?

Why does it need to be separated?

Answer 1

A mixture of many different compounds that boil at different temperatures, the different compounds burn under different conditions so crude oil needs to be separated to make useful fuels.

Question 2

What is a mixture?
How are the compunds in crude oil separated?
What are the products of this process?
What are fractions?

Answer 2

Two or more elements or compounds that not chemically combined, and the chemical properties of each substance is unchanged.
They are separated by distillation.
Fractions are the liquid products of crude oil that boil within different temperature ranges.

Question 3

What is crude oil mainly made up of?

What is the name given to most of these and what type of bonds do they contain?
Are they saturated or unsaturated and what does this mean about their structure?

Answer 3

Hydrocarbons; substance whose molecules contain only hydrogen and carbon.
Alkanes, they contain only single carbon-carbon bonds.

They are saturated, which means every carbon atom in an alkane molecule bonds to as many hydrogen atoms as is possible and no more hydrogen atoms can be added.

Question 4

What is the general formula for alkanes?

Answer 4

CnH2n+2

Question 5

How many carbon atoms do methane, ethane, propane and butane have?
What is a way of remembering the order?

Answer 5

1, 2, 3, 4 respectively

Monkeys Eat Peanut Butter

Question 6

In a displayed structure, what does a – represent?

How many bonds does each carbon atom have?

Answer 6

A covalent bond

4

Question 7

What is fractional distillation? (In general terms)

Answer 7

This is the process by which the different compunds in crude oil can be separated by evaporating the crude oil and allowing them to condense at the temperature of their boiling points.

Question 8

How does the boiling point and properties of hydrocarbons depend on their molecule size?
Where are hydrocarbons with the biggest molecules collected in the fractioning tower?

Answer 8

The bigger they are, the higher the boiling point, the more viscous they are, and the less flammable they are.
At the bottom

Question 9

Describe the different stages in fractional distillation. (4)
In stage one explain what a fractioning column is.

Answer 9

1) The crude oil is vaporised and fed into a fractioning column, this is a tall tower that is hot at the bottom and gets cooler going up the column.
2) The vapours move up the column getting cooler as they go up.
3) They condense to liquids when they reach the level in the tower that is at their boiling point.
4) Different liquids collect on the trays at different levels, there are outlets each level to collect the fractions.

Question 10

Where are hydrocarbons with the smallest molecules collected in the fractioning tower and why?
Give three other properties of these hydrocarbons?
What does this make them useful as?

Answer 10

They are collected at the top because the hydrocarbons with the smallest molecules have the lowest boiling points.
1) They have low viscosity
2) They are very flammable so ignite easily
3) They also burn with clean flames producing little smoke.
Fuels

Question 11

What are the products of complete combustion?

Answer 11

Carbon dioxide and water

Question 12

What may occur in a limited supply of air when a hydrocarbon fuel is burned?
What are the possible products of this and why are they produced?

Answer 12

Incomplete combustion
Carbon monoxide
Some of the hydrocarbons may not burn, this produces soot and unburnt hydrocarbons called particulates.

Question 13

Name one compound most fossil fuels contain, what is produced when these fossil fuels burn and what environmental problem does this product cause?

Answer 13

Sulphur compunds
When the fuel burns these sulphur compounds produce sulphur dioxide, which dissolves in water droplets and reacts with oxygen in air to cause acid rain.

Question 14

At the high temperatures of combustion, what may oxygen and nitrogen in the air combine to form?
What environmental problem does this product cause?

Answer 14

Nitrogen oxides dissolve in water droplets and react with oxygen in air to produce cause acid rain.

Question 15

Burning any fuel that contains carbon produces what?

What is this product and what environmental problem do scientists believe this causes?

Answer 15

Carbon dioxide which is a greenhouse gas that many scientists believe is the cause of global warming.

Question 16

Incomplete combustion of hydrocarbon fuels produces what poisonous gas?
What else does it produce and what environmental issue does this product cause?

Answer 16

Carbon monoxide

It can also produce tiny solid particulates that reflect sunlight and so cause global dimming.

Question 17

How are carbon monoxide and nitrogen oxides removed from exhaust systems in cars?
How are particulates removed?

Answer 17

They are removed by catalytic converters which are fitted to the exhaust systems.
Particulates can be removed by filters.

Question 18

What harmful substance is removed from the waste gases from power stations before they are released into the atmosphere?
Why is sulphur sometimes removed from fuels before they are supplied to users?

Answer 18

Sulphur dioxide

So that less sulphur dioxide is produced when the fuel is burned.

Question 19

What are biofuels?

From what is biodiesel made?

Answer 19

Biofuels are renewable fuels made from plant or animal products.
Biodiesel can be made from vegetable oils extracted from plants.

Question 20

Give three advantages and and one disadvantage of using biofuels?

Answer 20

Advantages:
1) They conserve diminishing resources
2) They reduce pollution
3) They are carbon neutral, the carbon dioxide released when they burn is equal to the amount of carbon dioxide taken in by the plants used to make the fuel when they were growing.
Disadvantages:
1) The plants that are grown to make biodiesel use large areas of farmland that could be used to grow food and help food shortages.

Question 21

What is ethanol?
What is it made from?
Why is it useful?

Answer 21

Ethanol is a biofuel made from sugar cane or sugar beet.
It is useful because it is a liquid, so can be stored and distributed like other liquid fuels and can be mixed with petrol.