Transcript Structures and Bonding

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Air Quality
(OCR 21st Century)
W Richards
The Weald School
Section C1.1 – Our air
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The Earth’s Atmosphere
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Present day atmosphere contains 78% nitrogen, 21% oxygen, 1% noble
gases and about 0.03% CO2
Carbon dioxide, water vapour
Oxygen
Nitrogen
Noble gases
Air
Air is a mixture of different gases consisting of small
molecules with large spaces between them:
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Evolution of the Earth’s Atmosphere
Carbon
dioxide
4 Billion years
Methane
Ammonia
Oxygen
Nitrogen
Others
Present day
atmosphere contains
78% nitrogen, 21%
oxygen, 1% noble
gases and about
0.03% CO2
3 Billion years
2 Billion years
1 Billion years
Present day
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Evolution of the Earth’s Atmosphere
Volcanic activity
releases CO2, methane,
ammonia and water
vapour into the
atmosphere. The water
vapour condenses to
form oceans.
4 Billion years
3 Billion years
Some of the oxygen is
converted into ozone.
The ozone layer blocks
out harmful ultra-violet
rays which allows for the
development of new life.
2 Billion years
1 Billion years
Green plants evolve which take in CO2 and
give out oxygen. Carbon from CO2
becomes locked up in sedimentary rocks as
carbonates and fossil fuels. Methane and
ammonia react with the oxygen and
nitrogen is released.
Present day
Carbon dioxide in the atmosphere
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The amount of CO2 in the atmosphere is affected by 3 things:
1) Geological activity moves carbonate rocks deep into
the Earth and they release ______ _______ into the
atmosphere during volcanic activity.
2) When fossil fuels are burned the carbon
contained in them reacts with _____ to form CO2.
3) Increased CO2 in the atmosphere causes a reaction
between it and _______. These reactions do not remove ALL
of the new CO2 so the greenhouse effect is still getting
_______!
Words – oxygen, seawater, carbon dioxide, worse
Pollution
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What happens to pollution?
Carbon dioxide causes global warming but some
of it can be removed by plants (photosynthesis)
or reactions with seawater.
Sulfur dioxide and nitrogen
dioxide cause acid rain which
damages trees and buildings.
Particulates (like in smog) can make buildings
dirty and worsen breathing difficulties.
Pollution
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Humans pollute the Earth in a number of ways:
Pollutant
Harmful to... Why?
Carbon dioxide
Environment
A greenhouse gas that causes
global warming
Nitrogen oxides
Environment +
humans
Causes acid rain and makes
asthma/breathing problems worse
Sulfur dioxide
Environment
Causes acid rain
Particulates (e.g.
Smoke)
Environment +
humans
Makes buildings dirty and makes
asthma worse
Carbon monoxide
Humans
Displaces oxygen in red blood cells
that can result in death
Section C1.2 – Pollution
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Fuels
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Fuels are substances that can be used to release useful
amounts of energy when they burn, e.g.
Wood
Oil
Gas
Coal
These fuels are called “fossil fuels” and
are described as being “non-renewable”.
The main element in these fuels is Carbon.
Burning Hydrocarbons
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Oil, petrol and diesel are all examples of
HYDROCARBONS. A hydrocarbon is a compound
made up of carbon and hydrogen.
Burning hydrocarbons will produce water, carbon dioxide and
energy:
H
H
H
O
C
O
H
Methane
+
O
O
Oxygen
C
H
O
H
O
Carbon
dioxide
+
O
O
H
H
Water
In this reaction the hydrocarbon is “oxidised” (“oxidised”
means that oxygen has been added and it’s the opposite of
reduced).
More information on oxygen
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Fuels need oxygen to burn. The more
oxygen they have, the quicker they will
burn. This is the principle behind oxyacetylene torches:
Other products of burning fuels
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Sulphur dioxide:
S
O
S
O
O
O
Sulphur
Nitrogen monoxide:
N
+
Oxygen
N
O
N
Sulphur
dioxide
O
N
Nitrogen
Nitrogen monoxide can
be further oxidised to
make nitrogen dioxide
(Nitrogen monoxide and
dioxide are jointly
referred to as NOx):
N
N
+
Oxygen
Nitrogen
monoxide
O
+
O
Oxygen
O
Nitrogen
monoxide
O
O
O
O
N
O
O
N
O
Nitrogen
dioxide
Conservation of mass in reactions
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In any reaction the total mass of products is
the same as the total mass of the reactants
Example 1 – Magnesium oxide and hydrochloric acid
H
Mg
O
H
Cl
Cl
Cl
1 x magnesium, 1 x oxygen, 2 x
hydrogen and 2 x chlorine atoms
Mg
H
Cl
H
H
C
H
O
O
O
O
H
Also 1 x magnesium, 1 x oxygen, 2
x hydrogen and 2 x chlorine atoms
Example 2 – Burning methane
H
O
C
O
O
H
H
O
O
H
H
Incomplete Combustion
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As well as producing carbon monoxide, incomplete combustion
can also produce soot:
Little
oxygen:
H
H
H
O
C
H
Methane
+
O
Oxygen
C
Carbon
“Soot”
+
H
O
H
O
Water
H
H
Burning Fossil Fuels
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Burning fossil fuels like oil and coal causes pollution.
Oil contains carbon:
H
H
H
C
H
O
O
O
O
C
O
O
H
H
O
O
H
H
Carbon dioxide is a “greenhouse
gas” – it helps cause global warming
Coal contains carbon, sulfur and other particles:
sulfur + oxygen
sulfur dioxide
Sulfur dioxide causes acid rain. Other particles can
cause “global dimming” – sunlight is absorbed by the
particles in the atmosphere.
Summary of pollutants
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Each of the following chemicals is a product of burning fossil
fuels. For each one summarise how it is made and what harm it
causes:
C
C
O
O
Carbon
monoxide
S
O
Carbon
dioxide
N
O
Nitrogen
monoxide
H
Sulfur
dioxide
H
Water
O
O
O
C
Carbon
O
N
O
Nitrogen
dioxide
C1.3 Improving Air Quality
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Removing Pollution
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There are many ways pollution can be reduced:
• Use less electricity/central heating
• Remove toxic chemicals before or
after they are burnt
• Use alternative energy sources, e.g.
wind power
Removing Sulfur
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Sulfur dioxide is clearly bad for the environment so it’s a good
idea to remove as much sulfur as possible:
Vehicles can remove sulfur
from fuels before they
are burned.
Power stations can remove
sulfur dioxide from waste
gases after combustion.
Wet Scrubbing
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“Wet scrubbing” is a term used to describe
the removal of sulfur dioxide and other
particles using seawater or an alkaline spray:
Step 1 – the dirty gas
is fed in through the
top.
Step 2 – the
“scrubbing liquid”
(seawater or
alkaline spray) is
fed in through
the side.
Step 3 – the
mixture is fed
into a cyclone
area where the
slurry is
collected at the
bottom of the
device.
Reducing Pollution from vehicles
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A number of suggestions:
1) Buy a new, smaller, more efficient car
2) Use legal limits (e.g. An MOT)
to enforce lower emissions
3) Use low sulfur fuels or convert your car to
run on biodiesel
4) Make sure your car has a catalytic converter:
Carbon monoxide + oxygen
Nitrogen monoxide + carbon monoxide
5) Use the train or a bus!
carbon dioxide
nitrogen + carbon monoxide
Alternative Fuels
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Car makers are currently researching two alternatives for
petrol and diesel-powered cars. What are the advantages and
disadvantages of each?
1) Electric cars
Advantages:
Disadvantages:
2) Biofuel cars
Advantages:
Disadvantages:
Making choices about pollution
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Choices concerning fighting pollution can be made on many
levels:
1) International
e.g. The Kyoto protocol in 1997
2) National
e.g. Car tax system, subsidies for greener technology
3) Local
e.g. Recycling schemes, transport,
congestion charges
4) Personal
e.g. Recycling, individual travel, reducing energy usage
in the home etc