2 Gases in the atmosphere Flashcards
(117 cards)
1
Q
What are the four most abundant gases present in unpolluted, dry air?
A
- Nitrogen.
- Oxygen.
- Argon.
- Carbon dioxide.
2
Q
What is the percentage of nitrogen in air?
A
78.1%
3
Q
What is the fraction of nitrogen in air?
A
About 4/5
4
Q
What is the percentage of oxygen in air?
A
21.0%
5
Q
What is the fraction of oxygen in air?
A
About 1/5
6
Q
What is the percentage of argon in air?
A
0.9%
7
Q
What is the percentage of carbon dioxide in air?
A
0.04%
8
Q
Are these the only gases in the air?
A
There are also very small amounts of other noble gases in the air.
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.
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.
11
Q
What is the apparatus used to find the percentage of oxygen in the air?
A
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.
13
Q
What is step 1 of this experiment?
A
The silica tube is heated strongly (roaring bunsen flame).
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.
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.
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.
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.
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.
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).
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.
21
Q
How do we know that the copper is in excess?
A
There will be some unreacted copper metal at the end.
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.
23
Q
What is an example of what the results table from this experiment will look like?
A
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.
25
What are the properties of nitrogen?
Nitrogen is very unreactive.
26
What happens if you put a lighted split into this 'air'?
It would be extinguished.
27
Why would a lighted splint be extinguished if we put it into this 'air'?
This is because oxygen is needed for things to burn.
28
Why has the volume of air decreased?
Because the oxygen has been removed as it reacts with the copper.
29
What is the symbol equation for this reaction?
2Cu + O2 ---> CuO
30
What is the word equation for this reaction?
Copper + oxygen ---> Copper (II) oxide.
31
How can we work out what the volume of oxygen is from this data?
We can work out from these data that the volume of oxygen that reacted was 100 - 79 = 21cm^3
32
How can we work out the percentage of oxygen in the air (method)?
The original volume of air was 100cm^3 so we can work out the percentage of oxygen in the air?
33
What is the formula that we use to find out the percentage oxygen in the air?
Percentage oxygen = 21/100 x 100 = 21%
34
Why can we use the rusting of iron to show the percentage of oxygen in air?
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.
35
What is an image of the apparatus that we use during the practical which uses the rusting of iron?
36
What do we need to do before we start the practical?
We need to know the volume of air present in the apparatus.
37
How can we find out the volume of air present in the apparatus?
We can find this by filling up the conical flask and connecting tube with water and then transferring the water to a measuring cylinder.
38
How do we know how far up to fill the conical flask up with water?
We mark the position of the bung and only fill with water to that point.
39
What do we do about the volume of the iron fillings?
We will assume that the small volume occupied by the iron fillings is negligible (very small compared to the overall volume).
40
What is the first step of this practical?
Set up the apparatus.
41
What is the second step of this practical?
Put wet iron filings into the conical flask.
42
What is the third step of this practical?
Record the initial reading on the gas syringe.
43
What is the fourth step of this practical?
Leave the apparatus in place for about a week, until the reading on the gas syringe stops changing.
44
What is the fifth step of this practical?
Record the final reading on the gas syringe.
45
What is an example of the results table from this practical?
46
How would we calculate the total volume of air inside the apparatus at the beginning of the experiment?
Volume of air in conical flask + volume of air in connecting tube + Initial reading on gas syringe.
130 + 12 + 92 =234cm^2
47
How could we calculate the total volume of 'air' in the apparatus at the end?
Volume of air in conical flask + Volume of air in connecting tube + Final reading on gas syringe.
130 + 12 + 43 = 185cm^3
48
How can we find the volume of oxygen used up?
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
How do we find the percentage of oxygen in the air?
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
What could happen sometimes when you do this experiment?
The answer comes out as less than 21%.
51
What are reasons as to why the answer may come out as less than 21%?
- 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
What can we use phosphorus to find out the percentage of oxygen in the air?
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
What is an image showing the apparatus we need to use in the practical involving phosphorus?
54
What is the first step of the practical which uses phosphorus?
The apparatus shown above is set up with the piece of phosphorus on an evaporating basin, which is floating in the water.
55
What is the second step of the practical which uses phosphorus?
The initial level of water is marked on the side of the bell jar with a waterproof pen or a sticker.
56
What is the third step of the practical which uses phosphorus?
The bung is removed from the bell jar and the phosphorus is touched with a hot metal wire in order to ignite it.
57
What is the fourth step of the practical which uses phosphorus?
The bung is quickly put back into the bell jar.
58
What is the fifth step of the practical which uses phosphorus?
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
What is the name of the white smoke which fills the bell jar?
Phosphorus oxide.
60
What is the sixth step of the practical which uses phosphorus?
When the level of water inside the bell jar stops rising, the final level is marked.
61
What is the seventh step of the practical which uses phosphorus?
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
What is important about the phosphorus?
It is important that there is still some phosphorus left on the evaporating basin at the end of the experiment.
63
What does this mean if some phosphorus is left on the evaporating basin?
That phosphorus was in excess.
64
Why have we used phosphorus in excess?
We have used an excess of phosphorus so that there is more than enough to react with all the oxygen.
65
What would happen if there was no phosphorus left?
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
What is the name to the reaction given when elements burn in oxygen?
Combustion reactions.
67
What is a characteristic when elements burn in pure oxygen as opposed to air?
Elements burn more brightly and rapidly in pure oxygen than in air.
68
Why do elements burn more brightly and rapidly in pure oxygen than in air?
Because air only contains 21% oxygen.
69
How does magnesium burn in oxygen?
Magnesium burns in oxygen with an extremely bright white flame to give a white, powdery ash of magnesium oxide.
70
What is the symbol equation for magnesium reacting with oxygen?
2Mg + O2 ---> 2MgO
71
What is formed?
A white powder.
72
Is this white powder soluble in oxygen?
This white powder formed is not very soluble in water but a very small amount does dissolve to form an alkaline solution.
73
What is the symbol equation for the formation of the white powder dissolving in water?
MgO + H2O ---> Mg(OH)2
74
How does sulfur burn in oxygen?
With a blue flame.
75
What is formed when sulfur burns in oxygen?
Poisonous, colourless sulfur dioxide gas is produced.
76
What is the symbol equation for when sulfur reacts with oxygen?
S + O ---> SO2
77
How does the sulfur dioxide dissolve in water?
The sulfur dioxide dissolves in water to form an acidic solution of sulfurous acid.
78
What is the chemical equation for this formation of sulfurous acid?
SO2 + H2O ---> H2SO3
79
How does hydrogen burn in oxygen?
With a pale blue flame.
80
What is the product when hydrogen burns in oxygen?
Water.
81
What is a symbol equation for the hydrogen burning in oxygen - ending in the formation of water?
2H2 + O2 ---> 2H2O
82
What happens if you ignite a mixture of hydrogen and oxygen?
It will explode.
83
What is this the basis of?
The 'squeaky pop' test for hydrogen.
84
What are the properties of oxides?
We can make some generalisations about the properties of oxides formed when elements burn in oxygen.
85
What are the properties of metal oxides?
- 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
What are the properties of non-metal oxides?
- 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
What is carbon dioxide?
Carbon dioxide is a colourless gas that is most easily made in the laboratory.
88
How is carbon dioxide made?
By the reaction between dilute hydrochloric acid and calcium carbonate in the form of marble chips.
89
What is a chemical equation for the reaction between dilute hydrochloric acid and calcium carbonate in the form of marble chips?
CaCO3 + 2HCl ---> CaCI2 + CO2 + H2O
90
What is another way that carbon dioxide can be obtained?
Carbon dioxide can also be obtained when metal carbonates are heated strongly.
91
How do most carbonates split?
They split to give the metal oxide and carbon dioxide when you heat them.
92
What is this splitting an example of?
Thermal decomposition?
93
What is thermal decomposition?
Decomposition reaction that requires heating to occur.
94
What is an example of thermal decomposition?
Copper (II) carbonate is a green powder which decomposes on heating to produce black copper (II) oxide.
95
What is the symbol equation for this reaction between copper carbonate?
CuCO3 ---> CuO + CO2
96
What is another example of thermal decomposition?
Calcium carbonate.
97
What are the conditions required for the decomposition of calcium carbonate?
It doesn't decompose unless it is heated at quite high temperatures.
98
Why is the thermal decomposition of calcium carbonate important?
This is a commercially important reaction because it is used to convert limestone (calcium carbonate) into quickline (calcium oxide).
99
What is the symbol equation for the thermal decomposition of calcium carbonate?
CaCO3 ---> CaO + CO2
100
What is the greenhouse effect?
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
When is carbon dioxide produced?
Carbon dioxide is produced when fossil fuels (coal, oil and gas) burn.
102
What is an example of when carbon dioxide is produced when fossil fuels burn?
When coal, which is mostly carbon burns in excess oxygen, carbon dioxide is produced.
103
What is the chemical equation for when coal produces carbon dioxide?
C(s) + O2(g) --> CO2 (9)
104
What is a petrol?
Petrol is a mixture containing many different hydrocarbons.
105
What is an example of a reaction when petrol burns?
2C8H18 + 25O2 ---> 16CO2 + 18H2O
106
What kind of gas is carbon dioxide?
A greenhouse gas.
107
What is a greenhouse gas?
Gases such as carbon dioxide which can trap heat radiated from the Earth's surface (originally from the sun).
108
When does the greenhouse effect occur?
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
What is UV?
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
What does the surface of the earth radiate?
The surface of the Earth (like any other
warm surface) radiates infrared (IR) radiation.
111
What happens to this IR radiation?
It is absorbed.
112
What is it absorbed by?
This IR radiation is absorbed by
molecules such as CO2 in the atmosphere.
113
What do these molecules then do?
These then give out this energy
again in all directions, heating the atmosphere.
114
What has happened to the level of carbon dioxide over the past 200 years?
For approximately the last 200 years the level of CO2 in the atmosphere has
been increasing.
115
Why have the carbon dioxide levels been rising?
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
What could the increasing level of carbon dioxide do?
It could contribute to climate change.
117
What are some characteristics of climate change, that are believed by scientists?
- Polar ice caps could melt
- Sea levels could rise
- There could be more extreme weather (such as floods, droughts and heatwaves)
