Chemistry 5070
Atmosphere and Environment
Atmosphere and Environment
Content
10.1 Air
10.2 Water
Learning outcomes
Candidates should be able to:
10.1 Air
(a) describe the volume composition of gases present in dry air
as 78% nitrogen, 21% oxygen and the remainder being noble
gases (with argon as the main constituent) and carbon dioxide
(b) describe the separation of oxygen, nitrogen and the noble
gases from liquid air by fractional distillation
(c) state the uses of oxygen (e.g. in making steel; oxygen tents in
hospitals; in welding)
(d) name some common atmospheric pollutants (e.g. carbon
monoxide; methane; nitrogen oxides (NO and NO2); ozone; sulfur
dioxide; unburned hydrocarbons)
(e) state the sources of these pollutants as
(i) carbon monoxide from incomplete combustion of carbon-containing
substances
(ii) methane from bacterial decay of vegetable matter
(iii) nitrogen oxides from lightning activity and internal combustion engines
(iv) ozone from photochemical reactions responsible for the formation of
photochemical smog
(v) sulfur dioxide from volcanoes and combustion of fossil fuels
(vi) unburned hydrocarbons from internal combustion engines.
(f) describe the reactions used in possible solutions to the problems
arising from some of the pollutants named in (d)
(i) the redox reactions in catalytic converters to remove combustion
pollutants
(ii) the use of calcium carbonate to reduce the effect of ‘acid rain’ and in
flue gas desulfurisation
(g) discuss some of the effects of these pollutants on health and on the
environment
(i) the poisonous nature of carbon monoxide
(ii) the role of nitrogen dioxide and sulfur dioxide in the formation of ‘acid
rain’ and its effects on organisms and buildings
(h) discuss the importance of the ozone layer and the problems involved
with the depletion of ozone by reaction with chlorine-containing
compounds, chlorofluorocarbons (CFCs)
(i) describe the carbon cycle in simple terms, to include
(i) the processes of combustion, respiration and photosynthesis
(ii) how the carbon cycle regulates the amount of carbon dioxide in the
atmosphere
(j) state that carbon dioxide and methane are greenhouse gases and
may contribute to global warming, give the sources of these gases and
discuss the possible consequences of an increase in global warming
10.2 Water
(a) state that water from natural sources contains a variety of
dissolved substances
(i) naturally occurring (mineral salts; oxygen; organic matter)
(ii) pollutant (metal compounds; sewage; nitrates from fertilisers;
phosphates from fertilisers and detergents; harmful microbes)
(b) discuss the environmental effects of the dissolved substances
named in (a)
(i) beneficial, e.g. oxygen and mineral salts for aquatic life
(ii) pollutant, e.g. hazards to health; eutrophication
(c) outline the purification of the water supply in terms of
(i) filtration to remove solids
(ii) use of carbon to remove tastes and odours
(iii) chlorination to disinfect the water
(d) describe how sea water can be converted into drinkable water
by desalination
Air:
Introduction:
 The mixture of different gases is called Air.
 Air contains Oxygen needed for respiration and carbon dioxide
needed for photosynthesis.
 The air also contains ozone that protects us from ultraviolet radiation
from sun.
Composition of Air:
Nitrogen
Oxygen
Carbon dioxide
Noble gases
Water vapours
Dust particles
78 – 79%
20%
0.03 – 0.04%
1%
Variable
Variable
The % of oxygen in air can be found using the
apparatus below.
Procedure:
• Total volume of air is recorded in both syringes.
• Copper powder is heated strongly.
• Pass the air back and forth strongly until there is no further change in volume.
• The total volume of gas left in the syringes is recorded.
Volume of oxygen in air = Initial volume of air – final volume of air
= 100 – 80 = 20
Hence % of oxygen = volume of oxygen in air / initial volume of air X 100
= 20 / 100 x 100 = 20%.
The chemical Reaction: 2Cu + O2 -------- 2CuO
Fractional Distillation of liquid Air:

Air is first cooled and compressed into liquid. Liquid air
is then separated into its constituents by fractional
distillation.
Nitrogen
(b.p = -1960C
Stage 1
Air
Stage 2
Liquid air
Cooling and
compression
Fractional
distillation
Argon
(b.p = -1860C
Oxygen
(b.p = -1830C
Air Pollution:

The condition in which air contains a high
concentration of certain chemicals that may harm
living things.
Common Air Pollutants:
1. Carbon monoxide:
 Sources of Carbon monoxide:
Incomplete combustion of fuel in vehicles.
 Harmful Effects:
Poisonous gas. Haemoglobin in our blood reacts more readily with CO
than O2, hence CO prevents the blood from carrying O2 that the body
needs.
 Preventive measures:
Using more air during combustion. Fitting motor cars with a catalytic
converter, where CO is converted to CO2 that is harmless.
2. Sulfur dioxide (SO2)
 Sources of Sulfur dioxide:
Burning of coal and petroleum in power stations and
other industries to provide energy. (Sulfur exists as an
impurity in both fuels.

Harmful Effects:
Irritates the eyes and causes breathing difficulties.
 Preventive measures:
Exhaust gases in power stations and other industries are
sprayed with wet calcium hydroxide or limestone to absorb
the sulfur dioxide.
Ca(OH)2 + SO2 ----- CaSO3 + H2O
CaCO3 + SO2
------- CaSO3 + CO2
3. Nitrogen oxide (NOx)
 Sources of Nitrogen oxide:
At high temperatures, the nitrogen and oxygen in the air combine to
form nitrogen oxides.
N2 + O2 ------- 2NO
2NO + O2 ----- 2NO2
(These reactions occur naturally in forest fires and during lightning).

Harmful Effects:
NOx can damage lungs. NOx can react with other air pollutants to form
ozone, which irritates the eyes and damages vegetation.

Preventive measures:

Lower the temperature of burning fuel. In power stations, water can
be sprayed into the burning fuel to lower the temperature.
NOx is passed over a platinum catalyst in a catalytic converter to
harmless nitrogen gas.

4. Acid Rain:
 Sources of Acid Rain:


SO2 in air reacts with oxygen and water to form sulfuric acid. The sulfuric
acid dissolves in rain water, forming acid rain, with a pH of about 4. Some
acid rain has been found to have a pH of less than 2.
2SO2 + O2 + 2H2O ------- 2H2SO4
NO2 also undergoes a similar reaction to form acid rain.
4NO2 + O2 + 2H2O ----- 4HNO3

Harmful Effects:




Acid rain corrodes metal structure like bridges and motor vehicles.
Acid rain also corrodes limestone buildings.
Acid rain endangers marine life.
Acid rain also reduces pH of soil, causing plants to die more quickly.

Preventive measures:
•
Solid calcium hydroxide or slaked lime is added to sea water and soil to
reduce acidity.
Acidic gases should be absorbed first before releasing them into the air.
•
5. Lead:

Sources of Lead:
Lead compounds are added into car fuel to make car engines run properly.

Harmful Effects:
Lead can cause brain damage, especially harmful to young children.

Preventive measures:
Use lead free petrol.
6. Chloro – fluoro carbons (CFCs):

Sources of CFCs:
Released when aerosols are used..

Harmful Effects:
Destroy the ozone layer (Cl atoms are released when sunlight decomposes
CFC).

Preventive measures:
Use CFC free aerosols.
Reducing Air Pollution:
The following are some important
steps to control air pollution.
1. Prohibition of the use of open fires
for the disposal of domestic and
industrial waste. Fire produce dust,
smoke and significant amount of air
pollutants.
2. Use lead free petrol.
3. Reduction of the permissible level
of sulfur in diesel.
4. Fitting of all petrol – driven
vehicles with catalytic converters.
Reducing the Effect of Acid Rain
The major contributors of acid rain are sulfur dioxide gas and oxides of
nitrogen. These can be removed from the exhaust fumes by the use of
catalytic converters and flu gas desulfurisation.
1. Catalytic converters:
A catalytic converter is attached to the exhaust system of a car. It contains
the catalysts platinum and rhodium.
When the hot exhaust gases pass over the catalysts, redox
reactions occur. The harmful pollutants are converted to
harmless substances.
Carbon monoxide is oxidised to carbon dioxide, oxides of
nitrogen are reduced to nitrogen.
2NO (g) + 2CO (g) ------ N2 (g) + CO2 (g)
Flue gas Desulfurisation:
 The waste gases formed, when fossil fuels undergo
combustion are called flue gases.
 The process of removing sulfur dioxide from the gases is
called desulfurisation.


When sulfur dioxide passes through the plant, it reacts with an
aqueous suspension of calcium carbonate to form solid calcium
sulfite.
CaCO3 (s) + SO2 (g) ----- CaSO3 (s) + CO2 (g)

The calcium sulfite is further oxidised to calcium sulfate by
atmospheric oxygen.
2CaSO3 (s) + O2 (g) --------- 2CaSO4

Besides calcium carbonate, calcium oxide can also be used for
desulfurisation.
CaO (s) + SO2 (g) ------- CaSO3 (s)
Water:
Introduction:
 Water is the most abundant liquid on earth.
 Liquid water covers about 70% of the earth surface.
Test for water:
 Anhydrous copper II sulfate can be used to detect the
presence of water.
 Water changes the colour of anhydrous copper II sulfate
from white to blue, forming hydrated copper II sulfate.
CuSO4 + 5H2O -------- CuSO4.5H2O
Anhydrous
Hydrated
White
Blue
Water Pollution:
1. Acids:
 Harmful effects:
Marine life cannot survive in low pH water.
Low pH water results I poor growth of vegetation.
 Source of Pollutant:
Acid rain of low pH decreasing pH of water.
2. Sewage:
 Harmful effects:
Health problems such as infections.
 Source of Pollutant:
Untreated household waste.
3. Nitrates and phosohates:
 Harmful effects:
Causes Eutrophication
 Source of Pollutant:
Excess fertilisers washed off from farmers crops.
4. Oil:
 Harmful effects:
Kills marine life as the oxygen passage into water
is sealed off.
 Source of Pollutant:
Oil spills from ships.
Purification of water:
Purification is done in the following stages:
1. Coagulation:
Chemicals like Aluminium sulfate (alum) is added to cause the
solid particles to clump together into bigger sizes before
filtration.
2. Sedimentation:
Large solid lumps will sink to the bottom of the water and can be
removed easily.
3. Filtration:
The water is then filtered to remove all solid particles.
4. Adding activated carbon:
To remove foul odour from water.
5. Chlorination:
Chlorine is added to kill germs and bacteria.
Desalination:

Desalination refers to the removal of salt from sea water.

One method is distillation, where pure water is distilled
and collected, leaving the salt behind.

Another process used now a days is reverse osmosis,
where water is ‘forced’ across a semi-permeable
membrane against a concentration gradient through the
exertion of pressure higher than osmotic pressure in
order to obtain pure water.