Ozone is a gas heavier than air. Why does ozone layer not settle down near the earth?
In stratosphere, the formation of $\mathrm{O}_3$ goes on continuously but $\mathrm{O}_3$ is also decomposed by UV- radiation between 240 nm to 360 nm .
$\mathrm{O}_3+\mathrm{H}_2 \xrightarrow{(240-360 \mathrm{~nm})} \mathrm{O}_2+\mathrm{O}$
The O -atom reacts will sand $\mathrm{O}_3$ molecule
$\begin{aligned} \mathrm{O}_3+\mathrm{O} & \longrightarrow 2 \mathrm{O}_2 \\ \text{Net reaction}\quad 2 \mathrm{O}_3 & \longrightarrow 3 \mathrm{O}_2\end{aligned}$
Thus, the reaction form a delicate balance in which the rate of $\mathrm{O}_3$ decomposition match the rate of $\mathrm{O}_3$ formation is a dynamic equilibrium exists and maintains a constant concentration of $\mathrm{O}_3$.
Some time ago formation of polar stratospheric clouds was reported over Antarctica. Why were these formed? What happens when such clouds break up by warmth of sunlight?
In summer season, nitrogen dioxide and methane react with chlorine monoxide and chlorine atoms forming chlorine sinks, preventing much ozone depletion, whereas in winter, special type of clouds called polar stratospheric clouds are formed over Antarctica. These polar stratospheric clouds provide surface on which chlorine nitrate gets hydrolysed to form hypochlorous acid. It also reacts with hydrogen chloride to give molecular chlorine.
$\mathrm{ClO}^{\infty}(g)+\mathrm{NO}_2(g) \longrightarrow \underset{\text { Chlorine nitrate }}{\mathrm{ClONO}_2(g)}$
$\mathrm{Cl}^{\infty}(\mathrm{g})+\mathrm{CH}_4(\mathrm{~g}) \longrightarrow{ }^{\infty} \mathrm{CH}_3(\mathrm{~g})+\mathrm{HCl}(\mathrm{g})$
$\mathrm{ClONO}_2(\mathrm{~g})+\mathrm{H}_2 \mathrm{O}(\mathrm{g}) \xrightarrow{\text { Hydrolysis }} \mathrm{HOCl}(\mathrm{g})+\mathrm{HNO}_3(\mathrm{~g})$
$\mathrm{ClONO}_2(g)+\mathrm{HCl}(g) \longrightarrow \mathrm{Cl}_2(g)+\mathrm{HNO}_3(g)$
When sunlight returns to the Antarctica in the spring, the sun's warmth breaks up the clouds and $\mathrm{HOCl}, \mathrm{Cl}_2$ are photolysed by sunlight.
$\mathrm{HOCl}(g) \xrightarrow{h v} \mathrm{O}^{\infty} \mathrm{H}(g)+\mathrm{Cl}^{\infty}(g)$
$\mathrm{Cl}_2(\mathrm{~g}) \xrightarrow{h v} 2 \mathrm{Cl}^{\infty}(\mathrm{g})$
The chlorine radicals thus formed, initiate the chain reaction for ozone depletion.
A person was using water supplied by Municipality. Due to shortage of water he started using underground water. He felt laxative effect. What could be the cause?
The laxative effect is observed only when the sulphates present in water have concentration greater than 500 ppm . Otherwise at moderate levels it is charmless.
Match the terms given in Column I with the compounds given in Column II.
| Column I | Column II | ||
|---|---|---|---|
| A. | Acid rain | 1. | $\mathrm{CHCl}_2-\mathrm{CHF}_2$ |
| B. | Photochemical smog | 2. | CO |
| C. | Combination with haemoglobin | 3. | CO$_2$ |
| D. | Depletion of ozone layer | 4. | SO$2$ |
| 5. | Unsaturated hydrocarbons |
A. $\rightarrow(3,4)$
B. $\rightarrow(4,5)$
C. $\rightarrow$ (2)
D. $\rightarrow$ (1)
A. Acid rain is due to oxides of carbon, sulphur (unsaturated hydrocarbon) and nitrogen.
B. Photochemical smog is formed by unburnt fuel (unsaturated hydrocarbon and $\mathrm{SO}_2$.
C. Carbon monoxide with haemoglobin is poisonous.
D. Chlorofluorocarbon $\left(\mathrm{CHCl}_2-\mathrm{CHF}_2\right)$ cause ozone depletion.
Match the pollutant(s) in Column I with the effect(s) in Column II.
| Column I | Column II | ||
|---|---|---|---|
| A. | Oxides of sulphur | 1. | Global warming |
| B. | Nitrogen dioxide | 2. | Damage to kidney |
| C. | Carbon dioxide | 3. | 'Blue baby' syndrome |
| D. | Nitrate in drinking water | 4. | Respiratory diseases |
| E. | Lead | 5. | Red haze in traffic and congested areas |
A. $\rightarrow$ (4)
B. $\rightarrow$ (5)
C. $\rightarrow$ (1)
D. $\rightarrow$ (3)
E. $\rightarrow$ (2)
A. Low concentration of sulphur dioxide causes respiratory disease e.g., asthma, bronchitis etc.
B. The irritant red haze in the traffic and congested place is due to oxides of nitrogen.
C. The increased amount of $\mathrm{CO}_2$ in air is mainly responsible for global warming.
D. Excess nitrate in drinking water cause methemoglobinemia (blue baby syndrome).
E. Lead can damage kidney, liver, reproductive system etc.