Green house effect leads to global warming. Which substances are responsible for green house effect?
The various gases which bring green house effect responsible for global warming are the following with relative contributions
| Various gases | Relative contribution |
|---|---|
| Carbon dioxide | 50% |
| Water vapour | 2% |
| Nitrous oxide | 4% |
| Ozone | 8% |
| Chlorofluorocarbons | 17% |
| Methane | 19% |
Acid rain is known to contain some acids. Name these acids and where from they come in rain?
Acid rain contains $\mathrm{H}_2 \mathrm{CO}_3, \mathrm{HNO}_3$ and $\mathrm{H}_2 \mathrm{SO}_4 \cdot \mathrm{H}_2 \mathrm{CO}_3$ is formed by the dissolution of $\mathrm{CO}_2$ of the air in which the water vapour present.
$$\mathrm{CO}_2+\mathrm{H}_2 \mathrm{O} \longrightarrow \mathrm{H}_2 \mathrm{CO}_3$$
Forest fire and lightning are the natural source of nitric oxide (NO). Nitrogen oxides are also produced by combustion engines, aircraft, furnaces, incinerators, industrial plants. Nitric oxide slowly reacts with atmospheric air and produce $\mathrm{NO}_2 \cdot \mathrm{NO}_2$ dissolves in water to form $\mathrm{HNO}_3$.
$$3 \mathrm{NO}_2+\mathrm{H}_2 \mathrm{O} \rightleftharpoons 2 \mathrm{HNO}_3+\mathrm{NO}$$
Sulphur oxides are produced by the burning of fossil fuels and in extraction of metals from their sulphide ores etc. Sulphur dioxide also produces sulphuric acid in the similar way.
$$\mathrm{SO}_2+\mathrm{O}_2+\mathrm{H}_2 \mathrm{O} \xrightarrow[\text { Metal oxide }]{\text { Soot particles }} \mathrm{H}_2 \mathrm{SO}_4+[\mathrm{O}]$$
Ozone is a toxic gas and is a strong oxidising agent even then its presence in the stratosphere is very important. Explain what would happen if ozone from this region is completely removed?
The ozone layer in the stratosphere is a natural feature of the earth's environment. The ozone layer exists between 20 to 35 km above the earth surface layer. This layer protects the earth from the harmful effects of the ultraviolet radiation of the sun.
A depletion of ozone layer is considered as a serious threat to all forms of life on the earth. A 5\% decrease in ozone concentration could increases the incidence of skin cancer by 20\%. Ultraviolet radiation is also the factor for disease of eye, including cataract formation. It can cause genetic mutations and destroy crops and other forms of vegetation. Aquatic animals and aquatic plants are generally affected by UV-radiation.
Dissolved oxygen in water is very important for aquatic life. What processes are responsible for the reduction of dissolved oxygen in water?
The process which are responsible for the reduction of dissolved oxygen in water are-use of phosphatic and nitrate fertilisers, detergents, the discharge of human sewage and organic waste from food, paper and pulp industries. The microorganisms which oxidise organic matter also utilise oxygen dissolved in water. Moreover during night, photosynthesis stops but the aquatic plants continue to respire, resulting in reduction of dissolved oxygen.
On the basis of chemical reactions involved, explain how do chlorofluorocarbons cause thinning of ozone layer in stratosphere?
Chlorofluorocarbons are introduced into the atmosphere from aerosol sprays in which they function as propellants and from refrigerating equipments in which they act as coolants. It is also used as solvents.
It has very long life and stay in atmosphere for years and ultimately reach the upper layer of atmosphere (stratosphere) where it decompose in presence of UV-radiation of the sun. On account of decomposition, it forms chlorine atom or free radicals.
$\mathrm{CF}_2 \mathrm{Cl}_2 \xrightarrow{h v}{ }^{\infty} \mathrm{CF}_2 \mathrm{Cl}+\mathrm{Cl}^{\infty}$
The active chlorine atoms then destroy the ozone layer.
$\begin{aligned} & \mathrm{Cl}^{\infty}+\mathrm{O}_3 \longrightarrow \mathrm{ClO}^{\infty}+\mathrm{O}_2 \\ & \mathrm{ClO}^{\infty}+\mathrm{O} \longrightarrow \mathrm{Cl}^{\infty}+\mathrm{O}_2\end{aligned}$
It has been found that one molecule of chlorofluorocarbon can destroy one thousand ozone molecules in the stratosphere.