Topic 5 - Fuels

Question 1

What are hydrocarbons?

Answer 1

Carbons made of carbon and hydrogen atoms only.

Question 2

What is crude oil?

Answer 2

A complex mixture of hydrocarbons, containing molecules in which carbon atoms are in chains or rings. It’s an important source of useful substances (fuels and feedstock for the petrochemical industry) and a finite (will run out) resource.

Question 3

What is fractional distillation?

Answer 3

The process of separating a mixture of liquids with different temperatures into different parts (fractions).

Question 4

What is a fraction of crude oil?

Answer 4

A smaller mixture of hydrocarbons that contain a similar number of carbons which have similar boiling points.

Question 5

How fractional distillation happens for crude oil?

Answer 5

1) Heat crude oil so that it vaporises
2) Pump heated vapours into a fractionating column
3) Fractionating is cooler at the top and hot at the bottom
4) Crude oil rises up the column
5) When they reach cool part of fractionating column it condense.
Boiling point = condensing point, each part has different condensing point so will move off at different points.

Question 6

What are the different fractions?

Answer 6

Gas
Petrol
Kerosene
Diesel oil
Fuel oil
Bitumen

Question 7

What’s gas used for?

Answer 7

Domestic heating and cooking.

Question 8

What’s petrol used for?

Answer 8

Fuel for cars.

Question 9

What’s kerosene used for?

Answer 9

Fuel for aircrafts.

Question 10

What’s diesel used for?

Answer 10

Fuels for some cars and trains.

Question 11

What’s fuel oil used for?

Answer 11

Fuel for large ships and in some power stations.

Question 12

What’s bitumen used for?

Answer 12

Surface roads and roofs.

Question 13

What are features of the top of the fractionating column?

Answer 13

• Shorter carbon chains
• Low boiling point
• Small molecules
• Ignites more easily
• Lower viscosity

Question 14

What are the features of the bottom of the fractionating column?

Answer 14

• Longer carbon chains
• High boiling point
• Higher viscosity
• Doesn’t ignite very easily
• Large molecules

Question 15

What the the hydrocarbons found in crude oil belong too?

Answer 15

A homologous series of chemicals called alkanes.
Alkanes:
• Ane in the name
• Single C-H bonds
• Saturated (fully bonded)

Question 16

What is the homologous series?

Answer 16

Methane - 1 carbon CH4
Ethane - 2 carbons C2H6
Propane - 3 carbons C3H8
Butane - 4 carbons C4H10
Pentane - 5 carbons
A series of compounds which have the same general formula, differ by CH2 in molecular formula from neighbouring compounds, show a gradual variation in physical properties and have similar chemical properties.

Question 17

What is complete combustion?

Answer 17

Happens when there is a good supply of oxygen. The products are water and carbon dioxide.
• Blue flame
• More energy released

Question 18

What is incomplete combustion?

Answer 18

Happens when there is a limited supply of oxygen. The products are carbon, carbon monoxide and water.
• Yellow flame
• Less energy released
• Produces soot

Question 19

How can you prove carbon dioxide and water are products of combustion?

Answer 19

• White powder in flask turns blue if water is present
• Limewater goes cloudy if CO2 is present

Question 20

Why is carbon monoxide dangerous?

Answer 20

• Tasteless
• Odourless
• Colourless
• Dense so sinks to the floor
• Nearer where people sleep

Question 21

Why is carbon monoxide toxic?

Answer 21

• Bunds with haemoglobin in red blood cells more strongly than oxygen
• Stops oxygen binding
• Stop respiration
• Stops oxygen reaching the brain
• People go unconscious and die

Question 22

How does acid rain form?

Answer 22

1) Sulfur impurities in fossil fuels make sulfur dioxide when they burn.
2) When fuels are burnt in engines, Nitrogen in the air reacts with oxygen in a hot engine to form nitrogen oxide.
3) Sulfur dioxide and nitrogen oxide rise into the atmosphere where they dissolve in the water droplets in the clouds to form sulphuric acid and nitric acid which falls as acid rain.

Question 23

What are problems of acid rain?

Answer 23

• Kills aquatic life
• Harms forests by damaging trees
• Corrodes stone and metal

Question 24

What are advantages of using hydrogen rather than petrol as a fuel for cars?

Answer 24

• Abundant (a lot of it, everywhere)
• The only waste is water (clean)
• More energy - efficient (releases more energy than petrol

Question 25

What are disadvantages of using hydrogen rather than petrol as a fuel for cars?

Answer 25

• Difficult to get because it’s locked in compounds that need to be extracted.
• Extracting hydrogen requires a lot of energy and heat which is expensive
• We don’t have hydrogen fuel infrastructure
• Dangerous, explosive if not stored properly
• Difficult to transport and store
• Most hydrogen is made from natural gas (non-renewable)

Question 26

What are non-renewable fossil fuels obtained from crude oil?

Answer 26

Petrol
Kerosene
Diesel oil

Question 27

What is a non-renewable fossil fuel found in natural gas?

Answer 27

Methane

Question 28

What is cracking?

Answer 28

Cracking involves the breaking down of larger saturated hydrocarbon molecules (alkanes) into smaller, more useful ones some of which are unsaturated (Alkenes)

Question 29

What is an alkane?

Answer 29

Saturated hydrocarbon, only has single bonds.

Question 30

What is an Alkene?

Answer 30

Unsaturated hydrocarbon which contain double bonds used to make plastics.

Question 31

Why crack hydrocarbons?

Answer 31

Long chain hydrocarbons are in low demand as they are less useful.
Shorter chain hydrocarbons can be used in the home and cars, and the Alkene can be turned into plastic.

Question 32

What are risks and preventions of cracking hydrocarbons?

Answer 32

• Suckback - water will rise up the delivery tube into hot test tube. Remove the delivery tube before turning off the heat.
• Hot test tube can cause burns. Allow to cool before tidying up.
• Heating to rapidly and violently. Gentle heating with blue flame.

Question 33

What is a polymer?

Answer 33

A large molecule containing chains of carbon atoms. They are made form joining many smaller Alkenes together.

Question 34

What happens as a polymer length increases?

Answer 34

As the polymer length increases so does the melting and boiling point. This is because as the polymer chain length increases there are more intermolecular forces between the polymers, therefore more energy is needed to melt them increasing their melting point. The longer chains also get tangled up with one another.