- No.vi. Comment: Why burning in open air is preferred?
Answer. Combustion in limited supply of, oxygen produces CO is air due to incomplete burning. Being colorless and odourless, its presence cannot be noticed easily and readily. When inhaled, it binds with the hemoglobin most strongly than that of oxygen. Thus, hindering the supply of oxygen in body. Exposure to higher concentration of CO causes headache and fatigue. If inhaled for a longer time it results in breathing difficulties and ultimately death. To avoid incomplete combustion burning is prefered in open air. In open air complete combustion takes place that produces CO2 instead of CO.
- No.vii. How sulphur containing compounds are emitted naturally?
Answer. Naturally occurring sulphur containing compounds are emitted in the bacterial decay of organic matter, in volcanic gases and forest fires. But the concentration of sulphur containing compounds in the atmosphere because of natural sources is very small as compared to the concentration of those compounds emitted by fossil fuel combustion in automobiles and industrial units.
- No. viii. How combustion of fossil fuels in internal combustion engine produces oxides of nitrogen?
Answer. Combustion of fossil fuels in internal combustion engines in thermal power stations and factories where huge amount of coal is burnt NO is formed by the direct combination of nitrogen and oxygen as shown in figure.
N2 + O2 2NO
However, it quickly reacts with air to form nitrogen dioxide. NO is highly toxic gas.
2NO + O2 ——— > 2NO
Formation of NO & NO2 on combustion of fossil fuel and causing air pollution
Mixture of these gases represented as NOX enters in the air through automobile exhaust and chimneys of thermal power stations and factories. It irritates breathing passage.
Test yourself 14.3 (ACID RAIN AND ITS EFFECTS)
- No. i. How acid rain is produced?
Answer. Burning of fossil fuels produces oxides of sulphur and nitrogen in air. Rain water converts SO2 into H2SO4 and NOX to HNO2 and HNO3. Normal rain water is weakly acidic because it consists of dissolved CO2 of the air. Its pH is about 5.6 to 6. But
rain water on dissolving air pollutants (acids) becomes more acidic and its pH reduces to 4. Thus, acid rain is formed on dissolving acidic air pollutants such as sulphur dioxide and nitrogen dioxide by rain water.
- No. ii. Why acid rain damages buildings?
Answer. Acid rain attacks the calcium carbonate present in the marble and limestone of buildings and monuments. Thus, these buildings are getting dull and eroded day by day because of acid rain attack.
- No.iii. How aquatic life is affected by acid rain?
Answer. Acid rain on soil and rocks leaches heavy metals (Al, Hg, Pb, Cr, etc) with it and discharges these metals into rivers and lakes. Aquatic life present in lakes, suffers because of high concentration of these metals. Especially high concentration of aluminum metal clogs the fish gills. It causes suffocation and ultimately death of fish. In this way aquatic life is affected by acid rain as shown in figure.