[CHEM] Chapter 10 - Air Atmosphere

1 DARRELL ER (COPYRIGHTED) © TOPIC 10: AIR & ATMOSPHERE DARRELL ER (COPYRIGHTED) ©

2 CHAPTER ANALYSIS THE ABOUT TIME EXAM WEIGHTAGE • Simple but content heavy chapter • Requires revision before test/exams • Straight forward questions Require knowledge of pollutants & effects • Will always link to other chapters: •  Chemical Equations, Redox Reaction • Light overall weightage • Constitute to 2% of marks for past 5 year papers DARRELL ER (COPYRIGHTED) ©

3 AIR & ATMOSPHERE COMPOSITION OF AIR POLLUTANTS KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

4 COMPOSITION OF AIR COMPOSITION OF AIR Air is a mixture of gases that largely made up of nitrogen and oxygen. The other gases are noble gases (like argon), carbon dioxide and water vapour. Percentage: Nitrogen - 78% Oxygen – 21% Carbon Dioxide – 0.03% DARRELL ER (COPYRIGHTED) ©

5 6 COMMON AIR POLLUTANTS METHANE (CH4) UNBURNT HYDROCARBONS SULFUR DIOXIDE NITROGEN OXIDES CARBON MONOXIDE OZONE (O3) DARRELL ER (COPYRIGHTED) ©

6 Summary Table MUST KNOW Gas Sources Effects Sulfur Dioxide Sulfur that are present in fossil fuels (crude oil) undergoes combustion Breathing difficulties Acid rain 2SO2 (g) + O2 (g) + 2H2O (l)  2H2SO4 (aq) 4NO2 (g) + O2 (g) + 2H2O (l)  4HNO3 (aq) Volcanic eruptions Nitrogen Monoxide / Nitrogen Dioxide NO and NO2 are formed in car engines or chemical factories under very high temperature and pressure Heat energy released by lightning during thunderstorms allows both nitrogen and oxygen in air reacts with each other Carbon Monoxide CO is produced from incomplete combustion of petroleum in vehicle engines CO binds to haemoglobin that is present in red blood cells, which would reduce its ability to transport oxygen, hence causing respiratory problems Methane Sheep and cows’ fart/burps Greenhouse gas that causes global warming Decomposition of plant and animal matter Unburnt Hydrocarbons Incomplete combustion of fuel in car engines and chemical plants Causes cancer Ozone Form from photochemical smog as a by-product from reaction between nitrogen dioxide and unburnt hydrocarbons in the presence of sunlight Breathing difficulties Damage crops DARRELL ER (COPYRIGHTED) ©

7 SULFUR DIOXIDE SULFUR DIOXIDE Sulfur is a type of impurity present in fossil fuels. When fossil fuels undergo combustion, sulfur would react with the oxygen in air to form sulfur dioxide. S (s) + O2 (g)  SO2 (g) Large volumes of sulfur dioxide can also produced during volcano eruptions. Harmful Effects: - Causes respiratory difficulties - Causes formation of acid rain, which results in erosion of buildings and environmental damages. DARRELL ER (COPYRIGHTED) ©

8 NITROGEN OXIDES NITROGENOUS OXIDES Under very high temperatures, nitrogen and oxygen in air reacts to form nitrogen monoxide (NO). N2 (g) + O2 (g)  2NO (g) Nitrogen monoxide can continue reacting with oxygen in air to form nitrogen dioxide (NO2). 2NO (g) + O2 (g)  2NO2 (g) NOX is usually produced in vehicle engines, power stations, factories and incinerators which are high temperature environments. NOX is can also be produced during thunderstorms and forest fires as well. Harmful Effects: - Causes irritation to our lungs - Causes the formation of acid rain, which results in erosion of buildings and environmental damages - NO2 may react to produce harmful ozone in the presence of sunlight DARRELL ER (COPYRIGHTED) ©

9 CARBON MONOXIDE CARBON MONOXIDE When carbon undergoes incomplete combustion due to the lack of oxygen, it produces carbon monoxide (CO). 2C (s) + O2 (g)  2CO (g) Incomplete combustion commonly occurs in vehicle engines. Carbon monoxide (CO) binds to haemoglobin that is present in red blood cells, which would reduce its ability to transport oxygen, hence causing respiratory problems. Harmful Effects: - Poisonous gas causing respiratory problems by reducing the body’s ability to transport oxygen effectively (by binding with haemoglobin in red blood cell). When you leave your car engine on while stationary, the air your engine takes in stagnant and after a while, incomplete combustion will cause the production of carbon monoxide! So try and turn off your engine if the car is going to stationary for a while! DARRELL ER (COPYRIGHTED) ©

10 METHANE METHANE Methane is a type of greenhouse gas that traps heat on Earth. Produced due to activities such as cattle farming (rearing of cows, sheeps etc…). These livestock produce methane in their digestive systems and release it in their farts and burps. Methane is also produced from bacteria decay process. The increase in the amount of methane produced causes enhanced greenhouse effect which in turn traps more heat on Earth, resulting in global warming. Harmful Effects: - Huge and increasing amounts of methane produced leads to enhanced greenhouse effect which causes global warming DARRELL ER (COPYRIGHTED) ©