Humans and their environment

04.20.2020
08:39:27
Biology/ grade 10- Today’s topic-Acid rain- course book - pages 302 and 303.
Main points-
Uses of air
The gases available in the air have many important applications.
Oxygen is used in steel making, welding and in breathing apparatus.
Nitrogen is used in food packaging, the production of ammonia and in the production of silicon chips.
Both of these gases are separated from air by fractional distillation.

Carbon monoxide

Sources: incomplete combustion of fossil fuels e.g: incomplete combustion of gasoline:
C8H18 + 9O2 → 5CO + 2CO2 + 9H2O
Adverse effects: poisonous, combining with hemoglobin in blood and prevents it from carrying oxygen.

Sulfur dioxide

Sources: combustion of fuels, natural gas and sulfide ores e.g: zinc blende (ZnS) in the extraction of zinc:
2ZnS + 3O2 → 2ZnO + 2SO2

Adverse effects: acid rain which causes corrosion to metal structures, buildings and statues made of carbonate rocks, damage to aquatic organisms. Pollutes crops and water supplies, irritates lungs, throats and eyes.

Oxides of nitrogen

Sources: reaction of nitrogen with oxygen in car engines and high temperature furnaces and as a product of bacterial action in soil.
Adverse effects: acid rain with similar effects as SO2 as well as producing photochemical smog and breathing difficulties, in particular for people suffering from asthma.



Nitrogen oxides

These compounds (NO and NO2) are formed when nitrogen and oxygen react in the high pressure and temperature conditions of internal combustion engines and blast furnaces.
Exhaust gases also contain unburned hydrocarbons and carbon monoxide.
Cars are fitted with catalytic converters which form a part of their exhaust systems.
Their function is to render these exhaust gases harmless.

Catalytic converters
They contain a series of transition metal catalysts including platinum and rhodium.
The metal catalysts are in a honeycomb within the converter to increase the surface area available for reaction.
A series of redox reactions occurs which neutralises the pollutant gases.
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