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2 Gases in the atmosphere Flashcards

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1
Q

What are the four most abundant gases present in unpolluted, dry air?

A
  • Nitrogen.
  • Oxygen.
  • Argon.
  • Carbon dioxide.
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2
Q

What is the percentage of nitrogen in air?

A

78.1%

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3
Q

What is the fraction of nitrogen in air?

A

About 4/5

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4
Q

What is the percentage of oxygen in air?

A

21.0%

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5
Q

What is the fraction of oxygen in air?

A

About 1/5

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6
Q

What is the percentage of argon in air?

A

0.9%

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7
Q

What is the percentage of carbon dioxide in air?

A

0.04%

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8
Q

Are these the only gases in the air?

A

There are also very small amounts of other noble gases in the air.

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9
Q

What is the basic principle followed by the practicals which show that air contains about one-fifth oxygen?

A

We react something with the oxygen in air and look at how much the volume decreases as the oxygen is removed.

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10
Q

What are the practicals that we use to show that air contains about one-fifth oxygen?

A
  • Using copper.
  • Using the rusting of iron.
  • Using phosphorus.
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11
Q

What is the apparatus used to find the percentage of oxygen in the air?

A
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12
Q

How do we know that the apparatus contains only 100cm3 of air?

A

The plunger on one of the gas syringes is pushed all the way in and the other moved out to 100cm3. We now know that the apparatus contains 100cm3 air.

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13
Q

What is step 1 of this experiment?

A

The silica tube is heated strongly (roaring bunsen flame).

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14
Q

What is step 2 of this experiment?

A

The plunger in the left-hand gas syringe is pushed in. This causes the air to pass over the heated copper. This pushes out the plunger on the right-hand gas syringe.

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15
Q

What is step 3 of this experiment?

A

The plungers are pushed in sequence so that the air in the system keeps passing over the heated copper. The pink-brown copper turns black as copper(II) oxide is formed.

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16
Q

What happens as the copper reacts?

A

The Bunsen Burner is moved along the tube so that it is always heating fresh copper.

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17
Q

What happens to the volume of the gas as oxygen is consumed

A

The volume of gas in the syringes falls as the oxygen is consumed.

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18
Q

What is step 4 of this experiment?

A

We keep pushing the plungers in and out until there is no change in volume.

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19
Q

What is step 5 of this experiment?

A

The apparatus is then allowed to cool to room temperature again before taking the final volume of gas (because gases expand as they are heated).

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20
Q

What do we need to make sure about the copper in this experiment?

A

We need to make sure that we use enough copper to react with all the oxygen in the air. So the copper must be in excess.

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21
Q

How do we know that the copper is in excess?

A

There will be some unreacted copper metal at the end.

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22
Q

What happens if we don’t use excess copper?

A

If we do not use enough copper then the value we get for the percentage of oxygen will be too low because not all of the oxygen will have been removed.

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23
Q

What is an example of what the results table from this experiment will look like?

A
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24
Q

Why have we put inverted commas around the word air?

A

Because we are now talking about air from which the oxygen has been removed, so it is mostly nitrogen.

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25
Q

What are the properties of nitrogen?

A

Nitrogen is very unreactive.

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26
Q

What happens if you put a lighted split into this ‘air’?

A

It would be extinguished.

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27
Q

Why would a lighted splint be extinguished if we put it into this ‘air’?

A

This is because oxygen is needed for things to burn.

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28
Q

Why has the volume of air decreased?

A

Because the oxygen has been removed as it reacts with the copper.

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29
Q

What is the symbol equation for this reaction?

A

2Cu + O2 —> CuO

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30
Q

What is the word equation for this reaction?

A

Copper + oxygen —> Copper (II) oxide.

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31
Q

How can we work out what the volume of oxygen is from this data?

A

We can work out from these data that the volume of oxygen that reacted was 100 - 79 = 21cm^3

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32
Q

How can we work out the percentage of oxygen in the air (method)?

A

The original volume of air was 100cm^3 so we can work out the percentage of oxygen in the air?

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33
Q

What is the formula that we use to find out the percentage oxygen in the air?

A

Percentage oxygen = 21/100 x 100 = 21%

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34
Q

Why can we use the rusting of iron to show the percentage of oxygen in air?

A

Iron rusts in damp air, using up oxygen as it does so. We can use this reaction to determine how much oxygen there is in the air.

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35
Q

What is an image of the apparatus that we use during the practical which uses the rusting of iron?

A
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36
Q

What do we need to do before we start the practical?

A

We need to know the volume of air present in the apparatus.

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37
Q

How can we find out the volume of air present in the apparatus?

A

We can find this by filling up the conical flask and connecting tube with water and then transferring the water to a measuring cylinder.

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38
Q

How do we know how far up to fill the conical flask up with water?

A

We mark the position of the bung and only fill with water to that point.

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39
Q

What do we do about the volume of the iron fillings?

A

We will assume that the small volume occupied by the iron fillings is negligible (very small compared to the overall volume).

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40
Q

What is the first step of this practical?

A

Set up the apparatus.

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41
Q

What is the second step of this practical?

A

Put wet iron filings into the conical flask.

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42
Q

What is the third step of this practical?

A

Record the initial reading on the gas syringe.

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43
Q

What is the fourth step of this practical?

A

Leave the apparatus in place for about a week, until the reading on the gas syringe stops changing.

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44
Q

What is the fifth step of this practical?

A

Record the final reading on the gas syringe.

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45
Q

What is an example of the results table from this practical?

A
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46
Q

How would we calculate the total volume of air inside the apparatus at the beginning of the experiment?

A

Volume of air in conical flask + volume of air in connecting tube + Initial reading on gas syringe.
130 + 12 + 92 =234cm^2

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47
Q

How could we calculate the total volume of ‘air’ in the apparatus at the end?

A

Volume of air in conical flask + Volume of air in connecting tube + Final reading on gas syringe.
130 + 12 + 43 = 185cm^3

48
Q

How can we find the volume of oxygen used up?

A

Total volume of air inside the apparatus at the beginning of the experiment - Total volume of ‘air’ in the apparatus at the end.
234 - 185 = 49cm^3

49
Q

How do we find the percentage of oxygen in the air?

A

Volume of oxygen used up
————————————– x 100
Total volume of air inside the
apparatus at the beginning of
the experiment.

49
—- x 100 = 21%
234

50
Q

What could happen sometimes when you do this experiment?

A

The answer comes out as less than 21%.

51
Q

What are reasons as to why the answer may come out as less than 21%?

A
  • The experiment was not left set up for long enough. The iron has not had enough chance to react with all the oxygen in the apparatus.
  • Not enough iron was added at the beginning. The iron must be in excess, that is, there must be enough iron to react with all the oxygen present.
52
Q

What can we use phosphorus to find out the percentage of oxygen in the air?

A

Phosphorus is a very reactive element that reacts with the oxygen in the air to form a phosphorus oxide. This oxide is very soluble in water. Phosphorus does not react with water.

53
Q

What is an image showing the apparatus we need to use in the practical involving phosphorus?

A
54
Q

What is the first step of the practical which uses phosphorus?

A

The apparatus shown above is set up with the piece of phosphorus on an evaporating basin, which is floating in the water.

55
Q

What is the second step of the practical which uses phosphorus?

A

The initial level of water is marked on the side of the bell jar with a waterproof pen or a sticker.

56
Q

What is the third step of the practical which uses phosphorus?

A

The bung is removed from the bell jar and the phosphorus is touched with a hot metal wire in order to ignite it.

57
Q

What is the fourth step of the practical which uses phosphorus?

A

The bung is quickly put back into the bell jar.

58
Q

What is the fifth step of the practical which uses phosphorus?

A

The phosphorus burns, the bell jar becomes filled with a white smoke and the level of water rises inside the bell jar. The smoke eventually clears as the phosphorus oxide dissolves in the water.

59
Q

What is the name of the white smoke which fills the bell jar?

A

Phosphorus oxide.

60
Q

What is the sixth step of the practical which uses phosphorus?

A

When the level of water inside the bell jar stops rising, the final level is marked.

61
Q

What is the seventh step of the practical which uses phosphorus?

A

To find how much the water level has changed, the ball jar is turned upside down, filled with water to each mark in turn and the water is poured into a large measuring cylinder.

62
Q

What is important about the phosphorus?

A

It is important that there is still some phosphorus left on the evaporating basin at the end of the experiment.

63
Q

What does this mean if some phosphorus is left on the evaporating basin?

A

That phosphorus was in excess.

64
Q

Why have we used phosphorus in excess?

A

We have used an excess of phosphorus so that there is more than enough to react with all the oxygen.

65
Q

What would happen if there was no phosphorus left?

A

Then we would probably get a lower value for the percentage of oxygen in the air because not al the oxygen might have been used up.

66
Q

What is the name to the reaction given when elements burn in oxygen?

A

Combustion reactions.

67
Q

What is a characteristic when elements burn in pure oxygen as opposed to air?

A

Elements burn more brightly and rapidly in pure oxygen than in air.

68
Q

Why do elements burn more brightly and rapidly in pure oxygen than in air?

A

Because air only contains 21% oxygen.

69
Q

How does magnesium burn in oxygen?

A

Magnesium burns in oxygen with an extremely bright white flame to give a white, powdery ash of magnesium oxide.

70
Q

What is the symbol equation for magnesium reacting with oxygen?

A

2Mg + O2 —> 2MgO

71
Q

What is formed?

A

A white powder.

72
Q

Is this white powder soluble in oxygen?

A

This white powder formed is not very soluble in water but a very small amount does dissolve to form an alkaline solution.

73
Q

What is the symbol equation for the formation of the white powder dissolving in water?

A

MgO + H2O —> Mg(OH)2

74
Q

How does sulfur burn in oxygen?

A

With a blue flame.

75
Q

What is formed when sulfur burns in oxygen?

A

Poisonous, colourless sulfur dioxide gas is produced.

76
Q

What is the symbol equation for when sulfur reacts with oxygen?

A

S + O —> SO2

77
Q

How does the sulfur dioxide dissolve in water?

A

The sulfur dioxide dissolves in water to form an acidic solution of sulfurous acid.

78
Q

What is the chemical equation for this formation of sulfurous acid?

A

SO2 + H2O —> H2SO3

79
Q

How does hydrogen burn in oxygen?

A

With a pale blue flame.

80
Q

What is the product when hydrogen burns in oxygen?

A

Water.

81
Q

What is a symbol equation for the hydrogen burning in oxygen - ending in the formation of water?

A

2H2 + O2 —> 2H2O

82
Q

What happens if you ignite a mixture of hydrogen and oxygen?

A

It will explode.

83
Q

What is this the basis of?

A

The ‘squeaky pop’ test for hydrogen.

84
Q

What are the properties of oxides?

A

We can make some generalisations about the properties of oxides formed when elements burn in oxygen.

85
Q

What are the properties of metal oxides?

A
  • Metal oxides are ionic compounds containing O2- ions.
  • Metal oxides are usually basic oxides, which means that they react with acids to form salts.
  • Metal oxides are usually insoluble in water. Those metal oxides that are soluble in water react with it to form alkaline solution containing hydroxide (OH-) ions.
86
Q

What are the properties of non-metal oxides?

A
  • Non-metal oxides are covalent compounds.
  • Non-metal oxides are usually acidic oxides, which react with alkalis/bases to form salts.
  • Non-metal oxides are often soluble in water and react with it to form acidic solutions containing hydrogen (H+) ions.
87
Q

What is carbon dioxide?

A

Carbon dioxide is a colourless gas that is most easily made in the laboratory.

88
Q

How is carbon dioxide made?

A

By the reaction between dilute hydrochloric acid and calcium carbonate in the form of marble chips.

89
Q

What is a chemical equation for the reaction between dilute hydrochloric acid and calcium carbonate in the form of marble chips?

A

CaCO3 + 2HCl —> CaCI2 + CO2 + H2O

90
Q

What is another way that carbon dioxide can be obtained?

A

Carbon dioxide can also be obtained when metal carbonates are heated strongly.

91
Q

How do most carbonates split?

A

They split to give the metal oxide and carbon dioxide when you heat them.

92
Q

What is this splitting an example of?

A

Thermal decomposition?

93
Q

What is thermal decomposition?

A

Decomposition reaction that requires heating to occur.

94
Q

What is an example of thermal decomposition?

A

Copper (II) carbonate is a green powder which decomposes on heating to produce black copper (II) oxide.

95
Q

What is the symbol equation for this reaction between copper carbonate?

A

CuCO3 —> CuO + CO2

96
Q

What is another example of thermal decomposition?

A

Calcium carbonate.

97
Q

What are the conditions required for the decomposition of calcium carbonate?

A

It doesn’t decompose unless it is heated at quite high temperatures.

98
Q

Why is the thermal decomposition of calcium carbonate important?

A

This is a commercially important reaction because it is used to convert limestone (calcium carbonate) into quickline (calcium oxide).

99
Q

What is the symbol equation for the thermal decomposition of calcium carbonate?

A

CaCO3 —> CaO + CO2

100
Q

What is the greenhouse effect?

A

Energy from the sun
—>
Energy re-emmited as IR radiation
—>
Some IR energy is absorbed by molecules like carbon dioxide
| |
| |
| |
The rest Energy transferred
is lost to other molecules,
into space. warming the whole
atmosphere.

101
Q

When is carbon dioxide produced?

A

Carbon dioxide is produced when fossil fuels (coal, oil and gas) burn.

102
Q

What is an example of when carbon dioxide is produced when fossil fuels burn?

A

When coal, which is mostly carbon burns in excess oxygen, carbon dioxide is produced.

103
Q

What is the chemical equation for when coal produces carbon dioxide?

A

C(s) + O2(g) –> CO2 (9)

104
Q

What is a petrol?

A

Petrol is a mixture containing many different hydrocarbons.

105
Q

What is an example of a reaction when petrol burns?

A

2C8H18 + 25O2 —> 16CO2 + 18H2O

106
Q

What kind of gas is carbon dioxide?

A

A greenhouse gas.

107
Q

What is a greenhouse gas?

A

Gases such as carbon dioxide which can trap heat radiated from the Earth’s surface (originally from the sun).

108
Q

When does the greenhouse effect occur?

A

The greenhouse effect occurs when
high-energy UV and visible light from the sun pass through the atmosphere
and warm up the surface of the Earth.

109
Q

What is UV?

A

The part of the electromagnetic radiation spectrum that has wavelengths between those of visible light and X-rays. It is invisible to the human eye.

110
Q

What does the surface of the earth radiate?

A

The surface of the Earth (like any other
warm surface) radiates infrared (IR) radiation.

111
Q

What happens to this IR radiation?

A

It is absorbed.

112
Q

What is it absorbed by?

A

This IR radiation is absorbed by
molecules such as CO2 in the atmosphere.

113
Q

What do these molecules then do?

A

These then give out this energy
again in all directions, heating the atmosphere.

114
Q

What has happened to the level of carbon dioxide over the past 200 years?

A

For approximately the last 200 years the level of CO2 in the atmosphere has
been increasing.

115
Q

Why have the carbon dioxide levels been rising?

A

This has occurred since the industrial revolution and is due
to the burning of fossil fuels and deforestation (cutting down trees to create more land for agriculture).

116
Q

What could the increasing level of carbon dioxide do?

A

It could contribute to climate change.

117
Q

What are some characteristics of climate change, that are believed by scientists?

A
  • Polar ice caps could melt
  • Sea levels could rise
  • There could be more extreme weather (such as floods, droughts and heatwaves)

Chemistry (22 decks)

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