Reducing the Effects of Environmental Issues (CIE IGCSE Chemistry: Co-ordinated Sciences (Double Award))

• Two of the main environmental issues are climate change and acid rain
• There are strategies that can be used to reduce the impact of these issues

Strategies to reduce climate change

• The production of greenhouse gases, specifically carbon dioxide and methane, needs to be reduced drastically to reduce climate change

Reducing carbon dioxide emissions 

• Some measures that can be taken include:
  • Being more ‘responsible consumers’ of energy by:
    • Using hydrogen and renewable energy supplies such as solar or wind energy instead of burning fossil fuels
    • Using more fuel-efficient vehicles, e.g. electric and hybrid cars
    • Reducing the number of vehicles on the road, e.g. using public transport, car-sharing
    • Recycling or reusing products made from crude oil and its derivatives
    • Reducing household energy consumption, e.g. turning lights out, using more efficient appliances
  • Reducing deforestation and / or re-forestation
    • Planting more trees, can help reduce the amount of atmospheric carbon dioxide through photosynthesis

Reducing methane emissions

• Reduce the amount of livestock farming
  • Methane is produced during digestion in animals

Extended tier only

Strategies to reduce acid rain

• Acid rain is caused by oxides of nitrogen and sulfur dioxide 
• The effects of acid rain can be reduced by decreasing the amount of oxides of nitrogen and sulfur dioxide that are produced
• Catalytic convertors in vehicles can be used to remove oxides of nitrogen

Reducing sulfur dioxide emissions

• Using fuels which contain low levels of sulfur
• Flue gas desulfurisation
  • This is the main way to reduce sulfur dioxide emissions
  • Waste gases from coal fired power stations are passed into a scrubbing chamber
  • They are sprayed with a wet slurry of calcium oxide and calcium carbonate 
  • The calcium compounds react with sulfur dioxide to produce calcium sulfate

Sulfur dioxide scrubber

The scrubber sprays a lime slurry over the waste gases to remove 90 - 95% of the sulfur dioxide

Extended tier only

Oxides of nitrogen

• 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
• Carbon monoxide is oxidised to carbon dioxide:

2CO + O₂ → 2CO₂

• Oxides of nitrogen are reduced to N₂ gas:

2NO → N₂ + O₂

2NO₂ → N₂ + 2O₂

• A single reaction can summarise the reaction of nitrogen monoxide and carbon monoxide within a catalytic convertor:

2NO + 2CO → N₂ + 2CO₂

Catalytic converters are designed to reduce the polluting gases produced in car exhausts

• Unburned hydrocarbons can also be oxidised to carbon dioxide and water:

C₈H₁₈ + 12½O₂ → 8CO₂ + 9H₂O