Determination of sulphur trioxide in the presence of sulphur
Assess the Evidence That Indicates the Increase in Atmospheric Concentration of Sulphur and Nitrogen...
Transcript of Assess the Evidence That Indicates the Increase in Atmospheric Concentration of Sulphur and Nitrogen...
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8/3/2019 Assess the Evidence That Indicates the Increase in Atmospheric Concentration of Sulphur and Nitrogen Oxides
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NSBHS Y12 Chemistry Alexander Peng
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Assess the evidence that indicates the increase in atmospheric
concentration of sulfur and nitrogen oxidesNatural sources of sulfur dioxide include the decomposition of organic matter by bacteria to produce
H2S which then is oxidised according to the equation 2H2S(g) + 3O2(g) 2SO2(g) + 2H2O(l). It is also
released by volcanic events such as eruptions from volcanos and geysers and is also released in
smoke from bushfires. As there has been no significant increase in volcanic eruptions or bushfires
then it is unlikely that this has caused an increase in atmospheric concentration of sulfur oxides.
Human sources of SO2(g) include the burning of fossil fuels, particularly coal and petroleum, and
industrial plants involving the smelting of sulfide ores.
Sulfide ores are smelted according to the equations:
Copper (Chalcopyrite): 2CuFeS2(s) + 5O2(g) + 2SiO2(s) 2Cu(l) + 2FeSiO3(l)+ 4SO2(g)Zinc: 2ZnS(s) + 3O2 2ZnO(s) + 2SO2(g)
This is because fuels often contain compounds of sulfur as impurities. For example, in coal, iron
sulfide (FeS2) is often found as an impurity, and when burnt it is oxidised to produce sulfur dioxideaccording to:
4FeS2(s) + 11O2(g) 8SO2(g) + 2Fe2O3(s)
As the amount of fuel combusted and ores smelted has been steadily increasing, then it is probable
that atmospheric concentration of sulfur oxides has been increasing too.
Similarly, nitrogen oxides are also naturally formed in the atmosphere during thunderstorms due to
the extreme heat of lightning. The heat causes the nitrogen molecules to break into their atomic
states and bond with either nitrogen or oxygen gases as the heat from the lightning dissipates. The
reactions can be represented as N2(g) + O2(g) 2NO(g) for nitric oxide and 2NO(g) + O2(g) 2NO2(g) for
nitrogen dioxide. As the number of lightning strikes is not increasing, this does not indicate an
increase in nitrogen oxides.
However, nitrogen oxides are also formed under high
temperatures found in the combustion of fuels, particularly in
car exhausts and thermal power stations. The high
temperatures, like those caused by lightning, provide the
activation energy for nitrogen and oxygen to react and form
NOx compounds. The comparative abundance of NO2 gases in
regions where millions of these engines exist indicates that
they have a significant effect on atmospheric concentration.
Quantitative analysis of Antarctic ice core samples by the CSIRO has shown steady increases in
concentrations of these oxides in recent times.
While the annual averages in cities has not increased significantly, the number of days where
concentrations have been above safe levels has increased dramatically.
However levels of these oxides are below 0.01ppm and difficult to detect and measure. There is no
reliable data before the 1950s, and it wasnt until the 1970s that sensitive gas analysis techniques
Figure 1Nitrogen Dioxide 2009
tropospheric density
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8/3/2019 Assess the Evidence That Indicates the Increase in Atmospheric Concentration of Sulphur and Nitrogen Oxides
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NSBHS Y12 Chemistry Alexander Peng
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allowed accurate and close monitoring of levels. Both SO2 and NO2 form sulphate and nitrate ions
which are hard to detect and measure.
Localised evidence also suggests increasing concentrations of SO2 and NO2, as the incidence of acid
rain has been increasing along with photochemical smog especially in Europe and China. Although
this is likely due to increasing concentrations of SO2 and NO2 there are other variables that could
cause or affect these events.
While some sulfur and nitrogen oxides are produced naturally, the amount released from natural
sources is not sufficient to cause a noticeable increase atmospheric concentration of these oxides.
The increase in acid rain in many industrial areas indicates a rise in acidic atmospheric non-metal
oxides due to emissions produced by industrial processes and analysis of artic core samples shows a
general trend worldwide of increasing concentrations of SOx and NOx gases. It is therefore probable
that the increase in SOx and NOx gases is largely human caused.