chap 12 maintaining air quality

• what is the percentage composition of air ?

  • 78% nitrogen
  • 21% oxygen
  • 0.04% carbon dioxide
  • 0.96% noble gases (mainly argon), water vapour and other gases
• why is nitrogen considered to be an inert gas ?

  it has nitrogen- nitrogen triple bonds which are relatively strong and hard to break so reactions that involve nitrogen have relatively high activation energies
• what are the uses of oxygen ?

  • combustion
  • support patients with breathing difficulties
  • 21% of oxygen in air is insufficient to oxygenate their blood
  • oxidiser in welding that joins pieces of metals together strongly
• what are the uses of argon and the other noble gases ?

  provide inert environment for high- temperature processes like in lightbulbs and in thermal purification of copper and steel
• how can gases in air be separated ?

  by fractional distillation
• what is the boiling point of nitrogen ?

  -196 °C
• what is the boiling point of argon ?

  -186 °C
• what is the boiling point of oxygen ?

  -183 °C
• what are air pollutants ?

  • they are harmful gases that should not be found in a sample of clean air
  • they cause harm to the environment and to living things
• what is air pollution ?

  it is the introduction of unwanted and harmful chemicals into the atmosphere
• what are some natural causes of air pollution ?

  lightning strikes, wildfires and volcanic eruptions
• what are some human causes of air pollution ?

  industrial emissions, combustion engine emissions and man- made fires
• name some air pollutants

  sulfur dioxide (SO2), nitrogen oxides (NO and NO2), carbon monoxide (CO), methane (CH4), unburnt hydrocarbons (CxHy), ozone (O3)
• name some air pollutants


  • sulfur dioxide (SO2)
  • colourless gas with a pungent odour
  • nitrogen oxides (NO and NO2)
  • NO is colourless and odourless
  • NO2 is red- brown and has a pungent smell
  • carbon monoxide (CO)
  • colourless and odourless gas that is very toxic
  • methane (CH4)
  • colourless and odourless gas that is highly flammable
  • unburnt hydrocarbons (CxHy)
  • colourless gas, naturally odourless but may be pungent due to fuel activities
  • ozone (O3)
  • pale blue gas with pungent odour
• what are the sources of sulfur dioxide ?

  • volcanic eruptions
  • combustion of fuels containing sulfur
• what are the sources of nitrogen oxides ?

  • vehicle combustion engines
  • lightning
• what is the source of carbon monoxide ?

  incomplete combustion of carbon- based fuels
• what are the sources of methane ?

  • anaerobic bacterial decay of organic substances
  • waste gases from cattle
• what is the source of unburnt hydrocarbons ?

  vehicle combustion engines
• what are the sources of ozone ?

  • lightning
  • reactions between oxygen molecules and sunlight in the upper atmosphere
  • reactions between unburnt hydrocarbons and nitrogen oxides in the presence of sunlight in the lower atmosphere
• what are the harmful effects of sulfur dioxide ?

  • cause breathing difficulties in humans and animals
  • react with oxygen in the air to form acidic compounds which dissolve in rain water, forming solutions of strong acids, forming acid rain
  • it kills plants and aquatic life
  • it corrodes buildings and structures made from limestone, marble and metals
• what are the harmful effects of nitrogen oxides ?

  • eye, lung irritation
  • causes breathing difficulties
  • NO2 react with oxygen in the air to form acidic compounds which dissolve in rain water, forming solutions of strong acids, forming acid rain
  • it kills plants and aquatic life
  • it corrodes buildings and structures made from limestone, marble and metals
• what are the harmful effects of carbon monoxide ?

  • it binds irreversibly with haemoglobin in our red blood cells
  • lowers the ability of the haemoglobin to transport oxygen to the rest of the body
  • results in the loss of consciousness and even death
• what are the harmful effects of methane ?

  major greenhouse gas that leads to global warming
• what are the harmful effects of unburnt hydrocarbons ?

  • cause eye and respiratory tract irritation
  • react with nitrogen oxides in the presence of sunlight to form photochemical smog, which appears as a brown haze
  • formation of smog also produces, ozone, sulfur dioxide and nitrogen dioxides
• what are the harmful effects of ozone ?

  • cause eye and respiratory tract irritation, leading to breathing difficulties
  • cause chest pains and headaches
  • slows down photosynthesis in plants, damaging crops
• describe the function of catalytic converters

  • contains a coating of catalysts made up of platinum, palladium and rhodium which speed up the conversion of harmful substances
  • arranged in honeycomb structures to maximise the surface area for gases to interact with
• how does the catalytic converter remove carbon monoxide + nitrogen dioxide ?

  2CO (g) + 2NO2 (g) -> 2CO2 (g) + N2 (g)
• how does the catalytic converter remove carbon monoxide ?

  2CO (g) + O2 (g) -> 2CO2 (g)
• how does the catalytic converter remove nitrogen dioxide ?

  2NO2 (g) -> N2 (g) + 2O2 (g)
• how does the catalytic converter remove octane ?

  2C8H18 (g) + 25O2 -> 16CO2 (g) + 18H2O (g)
• what is flue gas ?

  exhaust gas (waste) that emanates from combustion plants
• what does flue gas desulfurisation do ?

  it removes a significant proportion of the sulfur dioxide from the flue gas before it is released into the atmosphere
• what is the most common method of flue gas desulfurisation ?

  wet scrubbing using a calcium carbonate slurry

  • the slurry is formed when calcium carbonate, in the form of limestone, is mixed with water
• describe the process of wet scrubbing for flue gas desulfurisation with the help of chemical equations

  1. slurry droplets are sprayed through the flue gas and the calcium carbonate reacts with the sulfur dioxide to form calcium sulfite and carbon dioxide gas
  2. CaCO3 (s) + SO2 (g) -> CaSO3 (s) + CO2 (g)
  3. calcium sulfite is then further oxidise to form calcium sulfate by atmospheric oxygen
  4. 2CaSO3 (s) + O2 (g) -> 2CaSO4 (s)
  5. calcium sulfate can then be hydrated to form hydrated calcium sulfate (gypsum)
  6. CaSO4 (s) + 2H2O (l) -> 2CaSO4.2H2O (s)
• what is gypsum uses for ?

  making drywalls, fertilisers, plasters for sculptures, casts that stabilise fractured bones and making tofu
• how can the effects of acid rain be combated ?

  • liming
  • adding calcium carbonate to affected area
  • remove excess acid due to acid rain
• what are the limitations of liming ?

  • acid rain affect vast areas and there are limits to the regions that can be protected, such as territorial boundaries
  • expensive and effects are only temporary
• what is ozone layer ?

  it is a protective layer in the stratosphere that absorbs ultraviolet radiation, reducing the amount of UV radiation that reaches the earth's surface
• what happens when the ozone layer absorbs UV radiation ?

  the ozone molecules break up to reform oxygen

  3O2 (g) <-> 2O3 (g)