Download App

Atmospheric Pollution — CHEMISTRY STD 9 — Question

ICSE BoardEnglish MediumSTD 9CHEMISTRYAtmospheric Pollution5 Marks
Question
State the chemicals responsible for ozone layer destruction.
✓

Answer

Chemicals responsible for the destruction of the ozone layer:
(1) Excessive use of $CFCs:$
CFCs enter the atmosphere because of their excessive use in solvents, aerosol sprays, propellants, refrigerants and blowing agents for plastic foams.
CFCs are decomposed by UV rays to highly reactive chlorine which is produced in the atomic form.
$CF_2 Cl_{2(g)} \rightarrow CF_2 Cl_{(g)}+Cl_{(g)}$
This free radical $( Cl )$ reacts with ozone, and chlorine monoxide is formed.
$Cl_{(g)}+O_{3(g)}-ClO_{(g)}+O_{2(g)}$
This causes depletion of ozone, and chlorine monoxide further reacts with atomic oxygen to produce more free radicals of chlorine.
$ClO_{(g)}+O_{(g)} \rightarrow Cl_{(g)}+O_{2(g)}$
Again this free radical (CI) destroys ozone, and the process continues giving rise to large-scale ozone depletion.
(2) The fuel of planes:
When the fuel of planes burns, a large quantity of nitric oxide and other gases is emitted in the atmosphere. Nitric oxide reacts with ozone to form nitrogen dioxide and nitrogen trioxide.
$NO_{(g)}+O_{3(g)} \rightarrow NO_{2(g)}+O_{2(g)}$
$NO_{2(g)}+O_{3(g)} \rightarrow NO_{3(g)}+O_{2(g)}$
This also causes depletion of ozone.

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free

Explore more

More "[5 Mark Question Answer]" from Atmospheric Pollution→Atmospheric Pollution — all question types→CHEMISTRY STD 9 question papers→ICSE Board STD 9 question papers→ICSE Board question paper generator→

Similar questions

Match the atomic numbers 4, 14, 8, 15 and 19 with each of the following:
  1. A solid non-metal of valency 3.
  2. A gas of valency 2.
  3. A metal of valency 1.
  4. A non-metal of valency 4.
→
Describe briefly the ionic concept of oxidation and reduction. Give an equation to illustrate.
→
Give its
(i) mathematical expression
(ii) graphical representation and
(iii) significance.
→
${ }_{12}^{24} \mathrm{Mg}$ and ${ }_{12}^{26} \mathrm{Mg}$ are symbols of isotopes of magnesium.
(a) Compare the atoms of these isotopes with respect to:
i. the composition of their nuclei
ii. their electronic configurations
(b) Give reasons why the two isotopes of magnesium have different mass numbers.
→
Draw diagrams representing the atomic structures of the following:
  1. Sodium atom
  2. Chlorine ion
  3. Carbon atom
  4. Oxygen ion
→
A gas occupies $500 cm^3$ at a normal temperature. At what temperature will the volume of the gas be reduced by $20 \%$ of its original volume, the pressure is constant?
→
How can you say these are chemical changes? Give one reason for your answer.
→
 $800 cm^3$ of gas is collected at 650 mm pressure. At what pressure would the volume of the gas reduce by $40 \%$ of its original volume, the temperature remaining constant?
→
At constant temperature, the effect of change of pressure on the volume of a gas was as given below:
Pressure in atmosphere Volume in liters
$0.20$ $112$
$0.25$ $89.2$
$0.40$ $56.25$
$0.60$ $37.40$
$0.80$ $28.10$
$1.00$ $22.4$
(a) Plot the following graphs
  1. $P$ vs $V$
  2. $P$ vs $1/V$
  3. $PV$ vs $P$
Interpret each graph in terms of the law.
(b) Assuming that the pressure values given above are correct, find the correct measurement of the volume.
→
Our atmosphere acts as a greenhouse. Explain.
→