Fuels

Question 1

Crude oil

Answer 1

A fossil fuel formed over millions of years from ancient remains of marine organisms

Question 2

Hydrocarbons

Answer 2

Compounds that contain carbon and hydrogen atoms only

Question 3

Finite resources

Answer 3

• Are no longer being made

- Or are being made extremely slowly

Question 4

Fractional distillation

Answer 4

Used to separate crude oil into simpler more useful mixtures

Question 5

During fractional distillation:

Answer 5

• Oil is heated to evaporate it
• Vapours rise in a fractionating column
• The column has a temperate gradient (hot at the bottom, cool at the top)
• Each fraction condenses where it becomes cool enough and is piped out of the column

Question 6

Properties of fractions

Answer 6

Number of C and H atoms decreases up the column
Boiling point decreases up the column
Ease of ignition increases up the column
Viscosity decreases up the column

Question 7

Alkanes

Answer 7

A homologous series of compounds

Question 8

Uses of fractions

Answer 8

Gas- domestic cooking
Petrol-fuel for cars
Kerosene- fuel for aircraft
Diesel- fuel for some cars and trains
Fuel oil- fuel for large ships and some power stations
Bitumen- surfacing roads and roofs

Question 9

Features of a homologous series

Answer 9

• Molecular formulae of neighboring members differ by CH2
• Show a gradual variation in physical properties (e.g boiling points)
• Have similar chemical properties

Question 10

Chemical properties of alkanes

Answer 10

Alkanes undergo complete combustion. When they react completely with oxygen, carbon dioxide and water vapour form

Question 11

General formula of an alkane

Answer 11

CnH2n+2

Question 12

Incomplete combustion

Answer 12

Incomplete combustion happens when the supply of oxygen to a burning fuel is limited

Question 13

Incomplete combustion in vehicles

Answer 13

Faulty gas boilers can produce carbon monoxide and soot

Question 14

Carbon monoxide

Answer 14

Attaches to hemoglobin in red blood cells, preventing oxygen attaching instead. This reduces the amount of oxygen carried around the body by the bloodstream.

Question 15

Two problems caused by soot

Answer 15

• Soot can build up in chimneys where it may eventually cause fires
• Blackens buildings

Question 16

Acid rain

Answer 16

Rainwater is naturally acidic, but acid rain is more acidic than normal

Question 17

Sulfur dioxide

Answer 17

Hydrocarbon fuels may contain impurities such as sulphur compounds. When the fuel burns, the sulfur in these impurities is oxidizes to form sulfur dioxide.

This dissolves in the water in clouds to form a mixture of acids including sulfurous acid

Sulfurous acid is oxidized by oxygen in the air to form sulfuric acid

Question 18

The effects of acid rain

Answer 18

• Acid rain increases the rate of weathering of buildings made of limestone or marble
• Acid rain increases the rate of corrosion of metals, such as the iron in steel, weakening them

Question 19

Oxides of nitrogen

Answer 19

In car engines, fuel is mixed with air and ignited inside the engine. This causes temperatures high enough for nitrogen and oxygen in the air inside the engine to react together. These reactions produce various oxides of nitrogen (NOx)

These are atmospheric pollutants

Question 20

Nitrogen dioxide and acid rain

Answer 20

Nitrogen dioxide forms dilute nitric acid when it dissolves in the water in clouds

Question 21

Cracking

Answer 21

Cracking involves breaking covalent bonds in hydrocarbon molecules.

• Crude oil fractions are heated to evaporate them
• The vapors are passed over a catalyst containing aluminum oxide and heated to 650c
• This speeds up reactions that break down larger hydrocarbon molecules
• Smaller more useful molecules form and these can be used as fuels or for making polymers