Topics:

• Air
  • Air
  • Oxygen
  • How are gases cooled?
  • Separation of Air components
  • Pollution
  • Air Pollution
  • Catalytic Converter
  • Acid rain
  • Ozone
  • Green House effect
  • Global Warming
• Water
  • Physical Properties
  • Uses
  • Causes of Water Pollution
  • Removal of Impurities
  • Seawater Purification

Air:

Air:

Gaseous region around the earth

• Nitrogen: 78%
• Oxygen: 21%
• Argon: 0.09%
• Carbon dioxide: 0.03%

Oxygen:

Uses:

• respiration
  • C₆H₁₂O₆ (glucose) + 6O₂ → 6CO₂ + 6H₂O + Energy
• Burning and combustion
• Steel making
• Hospital oxygen tents
• Welding etc.

How to prove that only 20% Oxygen?

• Experiment by adding Copper to air
• Collect 100cm3 of air in a syringe
• Add copper and heat
• Copper will change to copper oxide
• You can see that 21% of the air will be reduced, which is the oxygen that is used up

How are gases cooled?

• Gases are compressed which leads to bonds being made.
• Gases are then suddenly expanded, and this results in immediate bond breaking.
• Bond breaking takes up heat and hence causes cooling.
• This is the method that is used in cooling instruments such as fridges where there is a compressor at the back.

Separation of Air components:

Nitrogen, Oxygen and noble gases are separated from air by the use of fractional distillation. Their difference in boiling points allow them to be separated.

Pollution:

Any substance that is added to the environment which causes an adverse effect.

Air Pollution:

CO:

• Properties:
  • Colorless
  • Poisonous
  • Odorless
• Natural Sources:
  • Forest fire: when incomplete combustion takes place in limited supply of oxygen
• Manmade Sources:
  • Transport vehicles
  • Railway engines
  • Air crafts
• Effects:
  • Combines with hemoglobin and has way more chances of combining then oxygen.
  • Disturbs the supply of oxygen to body cells

SO₂:

• Natural Sources:
  • Volcanic eruption
• Manmade Sources:
  • Power stations
  • Oil refineries
  • Combustion of fossil fuels
• Effects:
  • Suffocation (disturbance in respiration)
  • Decrease lung elasticity
  • Asthma
  • Causes acid rain
    • SO₂ + 3O₂ → 2SO₃
    • SO₃ + H₂O → H₂SO₄
    • Acid rains have PH lower than 7

Nitrogen Oxides, NO and NO2:

• Natural Sources:
  • lightening
• Manmade Sources:
  • Car engines
• Effects:
  • Acid Rain

Methane:

• Natural Sources:
  • Bacterial decay of vegetable matter
• Effects:
  • Acid Rain

Hydrocarbons:

• Unburnt hydrocarbons come from car engines.

Compounds of Lead:

• Lead compounds are carcinogenic (cancer causing)
• They cause a decrease in IQ as well.

Catalytic Converter:

• To prevent NO and CO from escaping engines, a catalytic converter is placed in vehicles.
• Inside the converter, carbon monoxide and nitrogen oxide react with each other in presence of catalysts and create carbon dioxide and nitrogen which are not harmful as the reactants.
• High temperature is used to make the two react.

Acid Rain:

• Acid rain is a serious environmental problem
• When compounds in atmosphere react and dissolve in the rainwater, the rainwater decreases in PH and becomes acid rain.
• Causes for acid rain are CO2, NO2, SO2
  • CO2 + H2O → H2CO3
  • SO2 + O2 à SO3 + H2O → H2SO4
  • NO +O2 à NO2 + H2O → HNO3
• The sources for these three are mainly industry and fossil fuel burning.
• Acid rain causes corrosion and kills plants. It also causes trouble in breathing.

Ozone:

• Ozone is a layer in the stratospheric region (25-28km above) which blocks high energy rays from reaching the earth which are otherwise harmful for us:
  • Cause skin cancer, heavy rainfall due to evaporation and floods as well.
• It is formed by O3 which is stable, and it is created in the presence of the UV light:
  • O2 →(UV light) 2 [O]
  • O2 + [O] → O3

Ozone destruction:

Ozone layer is being reduced due to CFCs or chloro-floro carbons that are created by refrigerators and other such machines. CFCl3 →( UV light) Cl + CFCl2 Cl + O3 → ClO + O2

Green House Effect:

• 50% of sunrays are reflected back from our Earth’s surface.
• Some gases such as carbon dioxide and methane are called greenhouse gases because they create a layer on the atmosphere that slows the energy of the coming rays.
• These rays are then not reflected back properly and are trapped at earth increasing temperature.
• This can cause global warming.

Global Warming:

• Global warming can result in high temperatures and loss of crops
• Melting of glaciers and ice and heavy floods
• Intense storms
• Drought threats etc.

Water:

Physical Properties:

• Colorless
• Transparent
• PH 7
• 0 degrees freezing point and 100 degrees boiling point
• Insulator
• Important for life

Uses:

• Drinking
• Power stations
• Construction
• Industries etc.

Causes of Water Pollution:

Physical Impurities:

Which we can see such as leaves, branches etc.

Biological Impurities:

Bacteria, viruses and diseases

Suspended Impurities:

Dissolved impurities such as salts mainly calcium chloride, calcium sulphate, magnesium chloride, magnesium sulphate etc.

Eutrophication:

Dissolved nitrates

Others:

Domestic garbage, soap and detergent, oil spillage and industrial waste as well.

Removal of Impurities:

Physical Impurities:

Grills and screening/ filtering: grills are placed that block out any physical impurities in water as water flows through them. Odors: Carbon is used to remove bad taste and odor from water.

Biological Impurities:

Chlorination: addition of chlorine kills the bacteria in the water

Suspended particles:

Sedimentation

Seawater Purification:

Sea water is salty water. In order to make it drinkable, we use the process of desalination. This consists of distilling the water as solids have higher boiling points, water evaporates first and is separated. Distillation can also be carried out by solar power or by electrolysis.

Lesson Tags

Air | Water | Detailed Notes For Preparation & Revision | O Level Chemistry 5070 and IGCSE Chemistry 0620

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