Air (D)

Question 1

State the composition of air

Answer 1

• Air is a mixture of different gases:
  
  • 78% nitrogen
  • 21% oxygen
  • 1% noble gases (mainly argon)
  • 0.04% carbon dioxide

Question 2

State the Sources of Sulfur Dioxide

Answer 2

• combustion of fossil fuels such as petrol and natural gas
• volcanic eruptions
• Note: sulfur present in the fossil fuels reacts with oxygen to form SO2
• equation: S + O2 → SO2

Question 3

State the Sources of Oxides of Nitrogen

Answer 3

• Combustion of nitrogen and oxygen from air in the internal combustion engines of vehicles at high temperature.
• Lightning activities (where nitrogen and oxygen in the air react to form oxides of nitrogen)
• *N2(g) + O2(g) → 2NO(g)
• 2NO(g) + O2(g) → 2NO2(g)*

Question 4

State the Sources of Carbon Monoxide

Answer 4

Incomplete combustion of carbon-containing fuels such as charcoal, wood, petrol.

Question 5

State the Sources of Methane

Answer 5

• anaerobic (in the absence of oxygen) bacterial decay of organic substances
• waste gases from cattle

Question 6

State the Sources of Unburnt Hydrocarbons

Answer 6

unburnt fuels in internal combustion engines of vehicles

Question 7

State the sources of Ozone

Answer 7

• Lightning activities
• from reaction of unburnt hydrocarbons and nitrogen oxides in the presence of sunlight in the lower atmosphere.
• from reaction between oxygen molecules and sunlight in the upper atmosphere

Question 8

What does catalytic converters do?

Answer 8

• oxidise CO into less harmful CO2
• reduce NO / NO2 to harmless nitrogen gas (N2).

Question 9

Why is the catalytic converter still unable to remove all pollutants?

Answer 9

• CO2 produced is a greenhouse gas that causes global warming
• Catalytic converters reduce air pollution (original pollutants from the engines are more harmful than CO2). But catalytic converters cannot eliminate pollution.

Question 10

How does photosynthesis and respiration regulate the amount of CO2 in atmosphere?

Answer 10

The amount of CO2 released into the atmosphere through respiration is the same as the amount of CO2 absorbed from the atmosphere through photosynthesis

Question 11

Why can’t we planting more trees decrease amount of CO2 in air?

Answer 11

Human activities such as burning / combustion of fossil fuels are releasing more carbon dioxide at a higher rate compared to the amount of carbon dioxide that can be absorbed by planting more trees via photosynthesis.

Question 12

State processes and equations that add and reduce CO2 in atmosphere

Answer 12

• Combustion (add CO2 to atmosphere)
  
  • CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (g)
• Respiration (add CO2 to atmosphere)
  
  • C6H12O6 (aq) + 6O2 (g) → 6CO2 (g) + 6H20 (l)
• Decomposition (add CO2 to atmosphere)
• Photosynthesis (remove CO2 from atmosphere)
  
  • 6CO2 (g) + 6H20 (l) → C6H12O6 (aq) + 6O2 (g)

Question 13

Harmful Effects of carbon monoxide

Answer 13

• Carbon monoxide is a toxic gas and causes death.
• It combines with haemoglobin in red blood cells and lower the ability of haemoglobin to transport oxygen to the rest of the body.

Question 14

Harmful effects of Sulfur Dioxide and Nitrogen Monoxide

Answer 14

• The gas causes breathing difficulties in humans and animals and leads to inflammation of the lungs

Question 15

How is acid rain formed from Nitrogen Monoxide and Sulfur Dioxide?

Answer 15

• SO2(g) + H2O(l) → H2SO3(aq)
• 2H2SO3(aq) + O2(g) → 2H2SO4(aq)
• 4NO2(g) + O2(g) + 2H2O(l)→4HNO3(aq)

Question 16

Harmful effects of Acid Rain

Answer 16

• sulfur dioxide (also nitrogen dioxide) reacts with oxygen and rain water to form acid rain which reduces pH of rivers harming aquatic life;
• corrodes buildings and structures (e.g. bridges) made of metals and limestone/ marbles (carbonates)
• leaches nutrients from the soil causing poor plat growth

Question 17

Harmful Effects of Methane and Carbon Dioxide

Answer 17

• Both are greenhouse gases contributing to global warming and melts ice caps