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zChemistry > Paper 2-SC20,21 > Flashcards

Paper 2-SC20,21 Flashcards

1
Q

What are natural gas and crude oil?

A

Natural resources formed from the ancient remains of microscopic animals and plants that once lived in the sea. The remains then became covered in sediment, over millions of years the remains gradually turned into natural gas and crude oil. The sediments turned into rock trapping the gas and oil. These resources are finite as they are limited to us.

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2
Q

What is crude oil?

A

A complex mixture of hydrocarbons.

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3
Q

What is a hydrocarbon?

A

A compound that contains hydrogen and carbon atoms only.

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4
Q

What are the first four alkanes?

A

Methane Ethane Propane and Butane.

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5
Q

What is the formula for Alkanes?

A

CnH2n+2

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6
Q

What is crude oil at room temperature?

A

Liquid.

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7
Q

What is crude oil used for?

A

Fuel and feedstock/raw materials for the petrochemical industry

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8
Q

What is natural gas?

A

A mixture of hydrocarbons in the gas state. Methane, the main hydrocarbon in natural gas is used for cooking.

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9
Q

Why is crude oil not used for fuel?

A

It is not runny enough or ignited easily enough for it to be useful as a fuel.

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10
Q

What is used to separate the hydrocarbons in the crude oil?

A

fractional distilation.

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11
Q

What is the fractionating column like?

A
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12
Q

Explain the trends in the different fractions.

A
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13
Q

What are most of the compounds in crude oil fractions?

A

Alkanes.

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14
Q

What are alkanes?

A

Hydrocarbons that only have single covalent bonds between the atoms in their molecules. The alkanes form a family or homologous series.

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15
Q

What are the features in the same homologous series?

A
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16
Q

What is a general formula?

A

The formula for a whole homologous series.

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17
Q

What are the similar chemical properties of alkanes?

A

They react with excess oxygen to produce carbon dioxide and water.

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18
Q

What is combustion?

A

Hydrocarbon fuels react with oxygen in the air when they burn. This is an example of an oxidation reaction and is called combustion.

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19
Q

What is complete combustion?

A

Only carbon dioxide and water are produced and energy is given out.

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20
Q

When does complete combustion happen?

A

When there is a plentiful supply of air or oxygen, for example when the air hole on a Bunsen burner is fully open.

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21
Q

What is the main hydrocarbon found in natural gas?

A

Methane.

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22
Q

What is incomplete combustion?

A

When there is a limited supply of air or oxygen such as when the air hole on a Bunsen burner is closed.

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23
Q

What happens during the incomplete combustion of a hydrocarbon?

A

Water is produced, energy is given out but less than with complete combustion and carbon monoxide, co2 and carbon are produced. Some carbon atoms are not fully oxidised to carbon dioxide so they oxidise to carbon monoxide and some make soot.

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24
Q

What are the problems with incomplete combustion?

A

Carbon monoxide is toxic and combines with heamoglobin in red blood cells, preventing oxygen combining, this refuced the amount of oxygen carried in the bloostream.

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25
Q

What does carbon dioxide form with water?

A

An acidic solution.

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26
Q

Why is rain water naturally acidic?

A

Because it constrains carbon dioxide from the air.

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27
Q

What is the pH of acid rain?

A

5.2

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28
Q

What causes acid rain to be more acidic?

A

Sulfur dioxide.

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29
Q

Why do hydrocarbons contain sulphur compounds?

A

They occur naturally as impurities and are not deliberately added.

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30
Q

What problems does acid rain cause?

A

Crops do not grow well when the soil is too acidic, excess acidity in rivers and lakes prevents fish eggs hatching and it can kill fish and insects.

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31
Q

What does acid rain do in link to the rate of weathering?

A

It increases the weathering of buildings made of limestone or marble and breaks down their structures. These rocks are almost pure calcium carbonate which reacts with sulfuric acid.

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32
Q

What does acid rain do to metals?

A

It increases the rate of corrosion of metals such as the iron in steel which weakens them.

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33
Q

What type of engines are car engines?

A

Internal combustion engines.

34
Q

What happens inside car engines?

A

Fuel is mixed with air and ignited inside the engine to react together, These reactions produce various oxides of nitrogen which are all atmospheric pollutants.

35
Q

What does NOx cause?

A

They cause acid rain.

36
Q

What does No2 form?

A

Dilute nitric acid when it dissolves in the water in clouds.

37
Q

What is nitrogen dioxide?

A

A toxic red-brown gas and can cause respirator diseases such as bronchitis.

38
Q

What stops harmful gases.

A

Catalytic converters in cars convert most of the NOx in exhaust gases to harmless nitrogen.

39
Q

What happens with the supply and demand of fractions?

A

There is normally more supply than demand of some fractions while the demand for others is higher than supply. Oil refineries use cracking to match supply with demand. Cracking also produces hydrocarbons with C C bonds which are used to make polymers(souble bond).

40
Q

How does cracking work?

A

Cracking involves breaking covalent bonds in hydrocarbon molecules. Crude oil fractions are heated to evaporate them. The vapours are passed over a catalyst containing aluminium oxide and heated to about 650 degrees. This speeds up reactions that break down larger hydrocarbons.

41
Q

Are Alkanes saturated?

A

Alkanes are saturated (their carbon atoms are joined by single bonds).

42
Q

Are alkenes saturated?

A

Alkenes are unsaturated (they contain a carbon-carbon double bond).

43
Q

What is petrol?

A

High demand and is used for fuel in cars. It is liquid at room temp so large amounts can be stored in the cars fuel tank. Petrol is easily ignited and its combustion releases a large amount of energy.

44
Q

What else can fuel cars?

A

Hydrogen can also be used to fuel cars, it is a by-product of cracking and can also be produced by reacting methane with steam. Unlike petrol and other hydrocarbon fuels the combustion of hydrogen produces water vapour but no carbon dioxide. It is easily ignited and releases lots of energy but it is gas at room temp so it is hard to store without compressed or liquidfied by cooling.

45
Q

How old is the earth?

A

4.5 billion years old.

46
Q

How do scientists investigate the atmoshpere before life evolved?

A

They look at evidence on earth and study the atmospheres of other planets and moons as these bodies don’t contain life so they are close to earths before life.

47
Q

What was the earths early atmosphere mostly?

A

Carbon dioxide with small amounts of water vapour and other gases with little to no oxygen.

48
Q

How did volcanoes affect the early atmosphere?

A

They release large amounts of some gases such as carbon dioxide and water vapour and small amounts of other gases including nitrogen.

49
Q

Was there lots of volcanic activity in the early atmosphere?

A

Yes.

50
Q

What supports the idea that the early atmosphere had lots of carbon dioxide.

A

Earth Venus and mars are rocky planets with volcanoes, the atmospheres of Venus and mars are mainly made of carbon dioxide thought to have been released by volcanoes.

51
Q

However what do some scientists think about the early atmosphere?

A

Some think that it was mostly nitrogen due to Titan. Titan is mostly nitrogen from volcanoes but titan is icy so thats why it is most likely false.

52
Q

When did the earth cool down and what happened?

A

4 billion years ago the earth cooled down causing water vapour to condense into liquid water which formed the oceans.

53
Q

What evidence is there that there was little to none oxygen?

A

Oxygen is not produced by volcanoes.

54
Q

How does iron pyrite show that there was little to none oxygen?

A

It is a compound that is broken down by oxygen and there was lots found in ancient rock.

55
Q

What happened when oxygen levels rose?

A
56
Q

Why did carbon dioxide levels decrease due to oceans?

A

Carbon dioxide dissolved in the oceans. Sea creatures used the carbon dioxide to form calcium carbonate shells that allowed more carbon dioxide to dissolve.

57
Q

What did photosynthesis do?

A

Uses carbon dioxide and releases oxygen.

58
Q

What were some of the earliest photosynthetic organisms?

A

Cyanobacteria which lived in shallow waters. They grew in huge colonies and produce sticky mucus which traps a layer of sand grains and other sediments. They need to move above the sediment layer to get sunlight . Over time the sediment layers build up to form rocky shapes.

59
Q

What are the rocky shapes called?

A

Stromatolities.

60
Q

What do the rocky structures show evidence for?

A
61
Q

What did cyanobacteria evolve into?

A

Other forms of life like plants, when land plants evolved about 500 million years ago there was another jump in oxygen levels.

62
Q

What percentage of the atmosphere today is oxygen?

A

21

63
Q

What is oxygen important for?

A

Aerobic respiration in organisms and combustion. This is used to test for it as pure oxygen will relight a glowing splint.

64
Q

What is the greenhouse effect?

A
65
Q

What are greenhouse gases?

A

The gases in the atmosphere that absorb energy.

66
Q

What are some of the greenhouse gases?

A

Carbon dioxide, methane, water vapour.

67
Q

How cold would the earth be without greenhouse gases?

A

-18 instead of 14.

68
Q

When did fossil fuels first start getting burnt?

A

1850.

69
Q

What is there a strong correlation between?

A

CO2 levels and surface temp.

70
Q

What is a casual link>

A

One thing causes another.

71
Q

What is there not betweenCO2 levels and surface temp?

A

A casual link.

72
Q

What do scientists need to do to show a casual link?

A

Collect evidence and explain how and why the correlation occurs. In this case, scientists want to know whether increasing CO2 levels could cause temps to rise or reverse.

73
Q

How is the amount of carbon dioxide in the air measured?

A

At monitoring stations around the world. Evidence for historical carbon dioxide leveels comes from ice cores and can go back 800,000 years. Antartica.

74
Q

Why can we measure CO2 levels better now?

A

Modern thermometers are less prone to error and have a greater resolution. Today we can also measure huge amounts of data from all around the world with sensors and satelites.

75
Q

What is a more powerful greenhouse gas methane or CO2?

A

Methane as it is better at absorbing infrared radiation so it allows less infrared radiation to leave the atmosphere.

76
Q

What is the main component of natural gas?

A

Methane.

77
Q

What also produces lots of methane?

A

Livestock farming especially cattle as the bacteria in their stomach that digests grass produces methane. Soil bacteria in landfil sites and in rice paddy fields also produce lots of methane.

78
Q

What are the effects of climate change?

A 
Rising temp 
Ice at south pole to melt 
rising sea levels
flooding
some animals may be forced to find cooler areas
extinction 
more extreme weather
79
Q

What will happen to the seas as a result of climate change?

A
80
Q

Limiting impact of climate change?

A

zChemistry (8 decks)

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