SC8 - Fuels and Earth Science

Question 1

What is a hydrocarbon?

Answer 1

A compound that contains hydrogen and carbon atoms only.

Question 2

What is crude oil?

Answer 2

A complex mixture of hydrocarbons which is a liquid at room temperature. It is formed from the ancient remains of microscopic animals and plants that once lived in the sea. They became covered by layers of sediment, which turns into rock, trapping the natural gas and crude oil.

Question 3

What is crude oil used for?

Answer 3

• fuels for vehicles, aircraft, ships, heating and power stations
• feedstock or raw materials for the petrochemical industry
  Petrochemicals are substances made from crude oil, such as poly(ethene) and other polymers.

Question 4

What is fractional distillation?

Answer 4

The use of distillation to separate liquids in a mixture, which have similar boiling points. A fractionating column is used.

Question 5

How does the fractionating column work in the fractional distillation of crude oil?

Answer 5

Crude oil is heated strongly to evaporate it, and the hot vapours are piped into the bottom of the column, where the column is hottest at the bottom and coldest at the top. The vapours rise through the column and cool down. They condense when they reach a part of the column that it cool enough (below their boiling points). The liquid falls into a tray and is piped away.

Question 6

What are the fractions of crude oil?

Answer 6

Bitumen, fuel oil, diesel oil, kerosene, petrol, gases

Question 7

Describe the trends in properties of the fractions of crude oil.

Answer 7

The number of carbon atoms in a molecule increases as you go down. The boiling point increases as you go down. The ease of ignition decreases as you go down (it is harder to harder to ignite bitumen than gases). The viscosity increases as you go down (gases flow more easily than bitumen).

Question 8

Describe gases (uses, approximate values for number of carbon atoms and boiling points).

Answer 8

Domestic heating and cooking
1-4 C atoms
-162 degrees C to -1 degrees C

Question 9

Describe petrol (uses, approximate values for number of carbon atoms and boiling points).

Answer 9

Fuel for cars
5-10 C atoms
30 degrees C to 200 degrees C

Question 10

Describe kerosene (uses, approximate values for number of carbon atoms and boiling points).

Answer 10

Fuel for aircraft
11-16 C atoms
160 degrees C to 250 degrees C

Question 11

Describe diesel oil (uses, approximate values for number of carbon atoms and boiling points).

Answer 11

Fuel for some cars and trains
17 - 20 C atoms
150 degrees C to 170 degrees C

Question 12

Describe fuel oil (uses, approximate values for number of carbon atoms and boiling points).

Answer 12

Fuel for large ships and some power stations
21-25 C atoms
300 degrees C to 400 degrees C

Question 13

Describe bitumen (uses, approximate values for number of carbon atoms and boiling points).

Answer 13

Surfacing roads and roofs
>35 C atoms
>360 degrees C

Question 14

What are the properties of a homologous series?

Answer 14

• molecular formula of neighbouring compounds varies by a CH2 unit
• they have the same general formula
• they show a trend in physical properties
• they have similar chemical properties

Question 15

What are the products of the complete combustion of a hydrocarbon?

Answer 15

Only carbon dioxide and water (energy is also given out)

Question 16

When does complete combustion happen?

Answer 16

When there is a plentiful supply of air or oxygen

Question 17

When does incomplete combustion happen?

Answer 17

When there is a limited supply of air or oxygen

Question 18

What are the products of the incomplete combustion of a hydrocarbon?

Answer 18

Water, carbon monoxide and particulate carbon (soot). Energy is also given out (though less than in given out in complete combustion).

Question 19

What is the danger of carbon monoxide gas?

Answer 19

Carbon monoxide is a toxic gas which is colourless and odourless. It combines with the haemoglobin in red blood cells, preventing oxygen combining. This reduces the amount of oxygen carried in the bloodstream, causing affected people to become sleepy or unconscious. Severe carbon monoxide poisoning can cause death.

Question 20

What is the problem with soot?

Answer 20

Soot can cause breathing problems if it collects in the lungs and it can blacken buildings.

Question 21

What causes acid rain?

Answer 21

Hydrocarbon fuels (such as petrol and diesel) often contain sulphur compounds (they are impurities). When the hydrocarbon fuel is burnt, the sulphur reacts with oxygen to form sulphur dioxide gas. Sulphur dioxide gas dissolved in water in clouds to form a mixture of acids including sulphurous acid, which is oxidised to form sulphuric acid. The mixture of acid and water falls as acid rain.

Question 22

What does acid rain do?

Answer 22

Causes weathering of buildings and statues (especially those made of limestone or marble). Excess acidity in lakes can kill fish and insects and prevent fish eggs hatching. Crops do not grow well when the soil is acidic. Acid rain also increases the rate of corrosion of metals (e.g. the iron in steel), weakening them.

Question 23

How are nitrous oxides made?

Answer 23

Car engines are ‘internal combustion 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. The reactions produce oxides of nitrogen, which are atmospheric pollutants.

Question 24

What are the problems with nitrous oxides?

Answer 24

They are a cause of acid rain. Nitrogen dioxide forms dilute nitric acid when it dissolves in water in the clouds. Nitrogen dioxide is a toxic red-brown gas, which can cause respiratory diseases such as bronchitis. Catalytic converters in cars concert most of the NOx in exhaust gases to harmless nitrogen.

Question 25

How are supply and demand problems with crude oil solved?

Answer 25

When crude oil is separated by fractional distillation, the volume of each fraction usually does not match the volume that can be sold (e.g. the demand for petrol is much higher than the supply, whereas the demand for fuel oil is much lower than the supply). Therefore, cracking is used to match supply with demand.

Question 26

What is cracking?

Answer 26

Cracking is a thermal decomposition reaction which breaks down long chain hydrocarbons into shorter chain hydrocarbons and alkenes

Question 27

How does cracking work?

Answer 27

Crude oil fractions are heated to evaporate them. The vapours are passed over a catalyst containing aluminium oxide and heated to about 650 degrees C. This speed up reactions that break down larger hydrocarbon molecules. Smaller, more useful alkanes form, which can be used as fuels, alongside alkenes, which can be used for making polymers.

Question 28

What are the benefits and drawbacks of using hydrogen as car fuel?

Answer 28

Hydrogen fuel has environmental benefits because the combustion of hydrogen gas produces water vapour, but no carbon dioxide. However, hydrogen is a gas a room temperature, which makes it difficult to store unless it’s compressed under high pressure or liquified by cooling.

Question 29

Which gases were believed to make up the Earth’s early atmosphere?

Answer 29

Mainly carbon dioxide with some ammonia and water vapour. Little or no oxygen.

Question 30

What was the influence of volcanic activity on the Earth’s early atmosphere?

Answer 30

Volcanoes release large amounts of carbon dioxide and water vapour and small amounts of nitrogen. There was lots of volcanic activity on the early Earth, so this probably helped form the early atmosphere.

Question 31

How do the atmospheres of Venus and Mars provide evidence for the composition of the Earth’s early atmosphere?

Answer 31

Earth, Venus and Mars are all rocky planets with volcanoes. The atmospheres of Venus and Mars are mainly made of carbon dioxide, thought to have been released by volcanoes. This supports the idea the the Earth’s early atmosphere had lots of carbon dioxide.

Question 32

How were the oceans formed on Earth?

Answer 32

About 4 billion years ago, the Earth cooled down. This caused water vapour in the atmosphere to condense to liquid water, which formed the oceans.

Question 33

What is the evidence that Earth’s early atmosphere contained little or no oxygen?

Answer 33

Oxygen is not produced by volcanoes. Also, iron pyrite has been found in very ancient rock, which is a compound that only forms if there is no oxygen present.

Question 34

What is the evidence that the oxygen levels slowly began to rise?

Answer 34

About 2.4 billion years ago, rocks containing bands of iron oxide started to form, suggesting oxygen levels increased at this time. There is also fossil evidence of microorganisms that may have produced this oxygen. Scientists think that the oxygen from these microorganisms reacted with iron in the early oceans, to produce insoluble iron oxides that formed layers in the seabed.

Question 35

What is the trend in atmospheric levels of oxygen and carbon dioxide over time?

Answer 35

Oxygen levels have increased a lot, while carbon dioxide levels have decreased a lot.

Question 36

How did the levels of carbon dioxide decrease?

Answer 36

Carbon dioxide dissolved in the oceans, reducing the amount in the atmosphere. Sea creatures used the dissolved carbon dioxide to form shells made of calcium carbonate. This allowed more carbon dioxide to be dissolved in the oceans.

Question 37

How did the levels of oxygen increase?

Answer 37

Some organisms began to use photosynthesis, which used up carbon dioxide and released oxygen. Cyanobacteria are some of the earliest photosynthetic organisms. Cyanobacteria grow in large colonies and produce a sticky mucus, which traps sand and sediment. Over time, this forms rocky shapes called stromatolites. Some stromatolites are over 3 billion years old. Cyanobacteria eventually evolved into other forms of life, including algae and plants. When land plants evolved, there was a jump in atmospheric oxygen levels (about 500 million yearsago).

Question 38

What are the estimates of the atmospheric composition today?

Answer 38

About 21% oxygen, 78% nitrogen and 1% other gases

Question 39

How does the greenhouse effect work?

Answer 39

Energy from the sun is transferred to the Earth by waves, such as light and infrared. Some energy is absorbed by the Earth’s surface, warming it up. The warm Earth emits infrared waves. Some gases in the air absorb energy transferred by the infrared waves. When these gases re-emit the energy, some of it goes back to the Earth’s surface and warms it, this is the greenhouse effect.

Question 40

What are some examples of greenhouse gases?

Answer 40

Carbon dioxide, methane, water vapour.

Question 41

What is the evidence to support the idea that carbon dioxide causes temperature rises?

Answer 41

Scientists can show in a lab that CO2 absorbs infrared. Satellite data confirms that as CO2 levels have increased, there had been a reduction in infrared waves from the Earth leaving the atmosphere.

Question 42

How are atmospheric levels of carbon dioxide measured?

Answer 42

Levels today are measured at monitoring stations around the world. Evidence for historical carbon dioxide levels comes from measuring the concentrations of the gas trapped in ice cores. This gives data going back 800 000 years.

Question 43

How are temperatures measured?

Answer 43

The oldest continuous temperature records are for central England and go back to 1659. However, they cannot be used to assess global temperature levels as they are only from one place. Continuous temperature measures from around the world exist from about 1880. Earlier measurements were not very accurate. Modern thermometers are less prone to error and have a greater resolution. We can also use sensors and satellites to measure temperature today.

Question 44

What has led to the increased amount of carbon dioxide in the atmosphere recently?

Answer 44

The increased burning of fossil fuels has released the CO2 which was previously stored underground in rocks.

Question 45

Why are levels of methane increasing?

Answer 45

Methane is released when oil and natural gas are extracted from the ground and processed. Livestock farming also produces a lot of methane. Soil bacteria in landfill sites and in rice ‘paddy’ filed also produce lots of methane.

Question 46

What are the effects of climate change on sea levels?

Answer 46

Rising global temperatures cause the ices at the South Pole and glaciers to melt, which causes sea levels to rise. Also, increased temperatures cause the water in the sea to expand. This may cause coastal flooding.

Question 47

What are the effects of climate change on animals?

Answer 47

Some animals may migrate from their natural habitats to find a cooler area to live. Some animals and plants may become extinct if they cannot adapt to the higher temperatures or migrate somewhere cooler.

Question 48

What is the effect of climate change on the ocean?

Answer 48

As more CO2 is released, more of this acidic gas will dissolve in seawater, lowering its oH. This can harm organisms living in the seas and oceans. Additionally, as ocean temperatures rise, it can cause coral to push out the photosynthetic algae that live in their tissues. These algae provide the colour of coral so coral ‘bleaching’ may occur. If coral remain ‘beached’ for too long, they can die.

Question 49

What is the effect of global warming on the climate?

Answer 49

Some areas have become drier, whilst others have become wetter. Extreme weather events are both more common and more severe. This includes hurricanes, tornadoes, droughts, floods and heatwaves.

Question 50

How can we limit the impact of climate change?

Answer 50

Using renewable energy resources can help reduce greenhouse gas emissions. There are suggestions of global engineering projects, such as reflecting sunlight back into space or capturing CO2 from the air and burying it back underground. However, this would require all countries to work together. Also, measures such as flood defences and irrigation systems can help people be more prepared for the effects of climate change.