In this chapter, we study about air, its pollutants, oxygen, hydrogen, water and more environmental issues and facts.
Air and Oxygen:
We all know that oxygen is important for human and animal life. It is even important for plant life. The process by which living organisms produce energy from their food is called respiration, and oxygen is essential for this process.
Oxygen is one of the main constituent of air. 20% of air is oxygen. The nitrogen in air is almost inert at room temperature, and after that the highest composition is of oxygen. So when any reaction says ‘react with air’, it actually means react with O2. However, we have to study other things about oxygen and the air today.
Combustion:
This is the process of burning. When anything burns, it requires fuel, heat and oxygen. Combustion actually means burning in the presence of oxygen.
Oxides:
When oxygen reacts with elements (metals or non-metals), the oxide of that element is formed. Oxygen is very reactive, and reacts with most metals.
For example, when oxygen O2 reacts with sodium Na, it forms sodium oxide Na2O.
When oxygen reacts with carbon C, it forms carbon’s oxide which is known as carbon dioxide, CO2.
Air Pollution:
The addition of poisonous gases in the environment is called air pollution. These gases include carbon monoxide CO, sulphur dioxide SO2, etc, and are called pollutant gases. Some pollutants like the oxides of sulphur and nitrogen are also acidic oxides and water soluble, so they cause acid rain and thus cause plants to die and buildings to be eaten away.
The main source of these pollutant gases entering the air is from the burning of fuels. All oils and fuels contain sulphur, and when they are burnt the sulphur reacts with the oxygen and forms sulphur dioxide gas.
When fuels like petrol and diesel are burnt in an internal combustion engine, the amount of oxygen present is limited. The carbon in these fuels reacts with the limited oxygen to form carbon monoxide, which is poisonously fatal. Had there been an excess of the oxygen, carbon dioxide would have been formed, which is a lot harmless compared to carbon monoxide. Also, the oxides of nitrogen that are released from car exhausts cause major pollution problems.
Don’t worry though; you won’t have to stop using your cars in order to save the environment! Engineers have already thought of this problem and figured out a way to reduce the pollution that our cars produce. They have made catalytic converters that are fit to car exhausts. Inside the converter is a special metal, mostly platinum, which acts as a catalyst. The function of this converter is to turn the poisonous exhaust gases we discussed earlier into harmless gases. Carbon monoxide is converted into carbon dioxide, while all oxides of nitrogen are converted into nitrogen gas. It does this by transferring oxygen atoms from the oxides of nitrogen to the carbon dioxide.
Ozone:
Ozone gas is actually three atoms of oxygen combined in form of a molecule. Even though it is useful in the atmosphere high up, it is a pollutant and harmful at ground level. It is formed when an electric spark passes through oxygen. Levels of ozone are high near railway tracks and electrified wires. It is also produced in car engines.
Ozone is harmful to the plants, and an irritant for nose and throat for humans. It reacts with ultraviolet radiation in sunlight to produce a photochemical smog, which is not fit for humans. However, up in the atmosphere it is beneficial as it helps keep out ultraviolet radiation from the sun.
Lead Compounds:
Lead compounds are usually added to petrol to make it heavier and thus more efficient. When this petrol burns, the lead particles stay as they are. These particles are then emitted out of the vehicle, and into the air. Such particles, when breathed in, can build up inside the body, and are toxic and poisonous. So these lead particles are also pollutants.