# Get the Knowledge that sets you free...Science and Math for K8 to K12 students

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## Air, Water & Soil

The world's next water pollution disaster Purification is the important process in metallurgy. Water is the important purifier of many ores since it dissolves many impurities. The waste water stored in tail ponds after purification has large quantities of metals and minerals ranging from benign to very toxic. There is a chance of contamination into terrestrial water, if there were any damage to the reservoir dams. Not only mining, the tail ponds of thermal power plants, gas and oil extraction have threat of damaging since they are not built with high-level engineering.
The toxic red mud sludge spill that took place in Hungary on 4th October 2010 is the one of the biggest ecological catastrophe. The dam of tail pond of a bauxite (aluminium) industry collapsed, freeing approximately one million cubic metres of liquid waste from red mud lakes. At least nine people died, and 122 people were injured.

## After completing the topic, the student will be able to:

• Examine the composition of air and discuss the functions and chemical reactions of constituents of air.
• Give the reasons for air pollution and suggest suitable methods for controlling air pollution.
• Define Greenhouse effect, Ozone depletion and Acid rains and point out the reasons for these effects.
• Discuss the properties of water, distinguish hard water and soft water.
• Give the advantages and disadvantages of hard water and the methods of water softening.
• Describe the process of polluted water treatment.
• Discuss the soil pollution and its effects.
• Suggest and adopt the suitable methods for controlling environmental pollution.
• Appraise the practice of green chemical methods to prevent environmental pollution.
Earth's atmosphere The atmosphere has a mass of about 5.15×1018 kg, three quarters of which is within about 11 km of the surface. The atmosphere becomes thinner and thinner with increasing altitude, with no definite boundary between the atmosphere and outer space.
Air

Life on Earth would not be possible without air. We need oxygen from the air to breathe. Plants need carbon dioxide from the air to prepare food through photosynthesis. Humans get energy due to the combustion of food inside the body, which is supported by air.

The region of air present around the Earth is called atmosphere. Most of the Earth's atmosphere is contained within 40 km of the planet's surface. With increase in altitude, air becomes thinner. Above 32 km, the air becomes very thin. Air is found in traces even above 100 km. This 40 km thickness is ultra thin when compared with the size of Earth (diameter about 13,000 km).
If the Earth were the size of an apple, its atmosphere would be about as thick as the skin of the apple!

The density of air is highest near the sea level and as we go higher, the density of air goes on decreasing. The composition of air also changes with the change in altitude. Air molecules would escape into outer space and be lost from Earth if there were no gravity. The air molecules surrounding Earth would settle to the ground if there were no sunlight. Solar–heated air molecules move at about 1500 km per hour and a few make their way up to more than 50 km in altitude. Earth’s gravity combined with the heat from the Sun, provide a layer of air more than 40 km thick that we call the atmosphere. This atmosphere provides oxygen, nitrogen, carbon dioxide, and other gases needed by living organisms. It protects the Earth’s inhabitants by absorbing and scattering cosmic radiation.

Composition of air

Air contains mostly nitrogen and oxygen, and small amounts of argon, carbon dioxide and water vapour. Other gases namely hydrogen, methane, nitrogen dioxide, ozone, helium, neon, krypton, xenon, carbon monoxide and sulfur dioxide are present in traces. The percentage of all these components also varies, but only slightly, from one location to another. The average composition of air by volume is given in the table. Air is a mixture of gases not a compound.

• The composition of air varies a little with location and altitude.
• Liquid air does not have a fixed boiling point, but it is approximately 78 K. It boils over a range of temperature.
• The components of liquid air can be separated by fractional distillation.
• We can obtain air, if we take all the components of air separately and mix them together in the same proportions in which they are present in the atmosphere. During the process of preparing air by mixing the various components, no chemical reaction takes place and no new substances are formed.
• Air exhibits the properties of all its individual components, such as nitrogen, oxygen, carbon dioxide etc.
• Air dissolves in water and is expelled when the sample of water is boiled. An analysis of dissolved air reveals that it is richer in oxygen and noble gases than atmospheric air. This is because oxygen and noble gases are more soluble in water than nitrogen is. The change in the proportion of the components of air when it is dissolved in water suggests that air is a mixture.