Matric Notes Chemistry 10th Chapter 14 Environmental Chemistry-I The Atmosphere Exercise Short Questions

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Exercise Short Questions:

Q1. Explain the phenomenon of decreasing temperature in Troposphere.

Ans. Decrease in Temperature:

In troposphere the concentration of gases decreases gradually with the altitude, correspondingly temperature also decreases at rate of 6 degree Celsius per kilometer. This is the region where all weather occur. Almost all aircrafts fly in this region.

Q2. Differentiate between primary and secondary air pollutants.

Ans. Primary pollutants:

Primary pollutants are the waste or exhaust products driven out because of combustion of fossil fuels and organic matter.

Examples:

Oxides of sulphur (SO₂ and SO₃); oxides of carbon (CO₂ and CO); oxides of nitrogen (specially nitric oxide NO); hydrocarbon (CH₄) ammonia and compounds of florine.

Secondary Pollutants:

Secondary pollutants are produced by various reactions of primary pollutants.

Examples:

Sulphuric acid, carbonic acid, nitric acid, hydrofluoric acid, ozone and peroxy acetyl nitrate (PAN).

Q3. State the major sources of CO and CO₂ emission. (Write down the sources of oxides of carbon).

Ans. Sources of CO and CO₂ Emission:

1. Both of these gases are emitted due to volcanic eruption and decomposition of organic matter naturally.
2. The major source for the emission of these gases is combustion of fossil fuels (coal, petroleum and natural gas). Fossil fuels burnt in combustion engine of any type of automobile, kiln of any industry, or open air fires emit CO₂ and CO.
3. Forest fires and burning of wood also emit CO₂ and CO. Especially, when supply of oxygen is limited, emission of CO dominates.

Q4. CO₂ is responsible for heating up atmosphere. How?

Ans. CO₂ is green house gas. In atmosphere it acts like a glass wall of greenhouse. It absorbs infrared radiations and allows visible light to pass through it. So, it absorbs most of outgoing radiations which results in heating of atmosphere.

Q5. CO is a hidden enemy. Explain its action.

Ans. CO is poisonous gas. Being colourless and odourless its presence can not be noticed easily and readily. It binds with haemoglobin of blood and forms carboxy haemoglobin. So, supply of oxygen is cut off. If inhaled for a longer time, it causes breathing difficulty which leads to death.

Q6. What threats are to human health due to SO₂ gas as air pollutant?

Ans. SO₂ is colourless gas. It has irritating smell. It causes suffocation, irritation and severe respiratory problems to asthmatic people.

Q7. Which air pollutants is produced in an anaerobic decomposition of organic matter?

Ans. CH₄ is an air pollutant produced by anaerobic decomposition.

Q8. How does acid rain increase the acidity of soil?

Ans. A number of acids e.g., H₂SO₄, HNO₃ and H₂CO₃ which are main components of acid rain come on the surface of Earth along with rain and results in acidity of soil.

Q9. Point out two serious effects of ozone depletion.

Ans. i) It causes skin cancer

ii) Depletion of ozone layer will increase infectious diseases like malaria.

Q10. How does ozone layer form in stratosphere?

Ans. Ozone layer is formed by the reaction of O₂ and atomic oxygen in the mid of stratosphere.

The concentration of ozone remains nearly constant through a series of complex radiations.

O + O₂ ----> O₃

Q11. Why does the 75% of the atmospheric mass lie within the troposphere?

Ans. About 99% of atmospheric mass lies within 30 kilometers of the surface and 75% lies within the lowest 11 kilometers in troposphere due to gravitational force of Earth.

Q12. How is ozone layer being depleted by chlorofluorocarbons? OR How do chlorofluorocarbons damage the ozone layer?

Ans. Chlorofluorocarbons (CFC's) (used as refrigerants in air conditioners and refrigerators) are major cause of depletion of ozone layer. These compounds leak in one way or other, escape and diffuse to stratosphere. The ultraviolet radiations break the C-Cl bond in CFCl₃ and generates chlorine free radicals as;

CFCl₃ -----UV---> CFCl₂ + Cl^o (free radicals)

These free radicals are very reactive. They react with ozone to form oxygen as:

O₃ + Cl^o (free radicals) -----> O₂ + OCl^o (free radicals)

OCl^o (free radicals) -----> O^o (free radicals) + Cl^o (free radicals)

O^o (free radicals) + O^o (free radicals) -----> O₂

A single chlorine free radical released by the decomposition of CFCs is capable of destroying upto many lacs of ozone molecules.