Air and Atmosphere

Exercise I

Question 1

Give one use for each of the following inert gases:

(a) Argon

(b) Helium

(c) Neon

(d) Radon

(e) Krypton

(f) Xenon

Answer

(a) Argon is used to fill electric bulbs which improves the quality and life of the bulb.

(b) Helium is used for filling up weather observation balloons.

(c) Neon is used in making advertising signboards and tube-lights.

(d) Radon is used for cancer treatment.

(e) Krypton is used for photography.

(f) Xenon is used for photography.

Question 2

Answer the questions put against each of the following constituents of air:

(a) Nitrogen : Explain its significance for plants and animals.

(b) Oxygen : What is the percentage proportion of oxygen in air? Why is oxygen called active air?

(c) Carbon dioxide : "Although carbon dioxide plays no role in respiration, all life would come to an end if there is no carbon dioxide in air." Support this statement with relevant facts.

(d) Water vapour : Explain its role in modifying the earth's climate.

Answer

(a) Nitrogen provides a vital nutrient protein to all living beings i.e. plants and animals essential for their growth and development. Plants convert nitrogen into proteins while human beings and animals get it from plants.

(b) Oxygen constitute about 21% of air by volume. Oxygen is called active air because it supports combustion and life.

(c) "Although carbon dioxide plays no role in respiration, all life would come to an end if there is no carbon dioxide in air." This statement is justified by following two facts:

1. Carbon dioxide is essential for photosynthesis process as green plants required it to prepare food and all other animals including human beings depends upon plants for food.
2. It minimizes heat loss by radiation by reflecting heat back to earth's surface particularly at night thus balances the temperature of earth.

(d) The presence of water vapour in air causes rain. At low temperatures water vapour condenses to form snow, sleet, mist, frost, hail, dew, fog, etc. In this way water vapour plays an important role in modifying earth's climate.

Question 3

Define the following terms:

(a) Pollutants

(b) Acid rain

(c) Global warming

(d) Smog

Answer

(a) Pollutants are the undesirable substances present in air that are harmful to plants and animals.

(b) A rain which is acidic in nature is called acid rain. Gases like sulphur dioxide, nitrogen dioxide etc. react with water present in air to form sulfurous acid, sulfuric acid, nitrous acid and nitric acid respectively that comes down to earth with rain water in form of acid rain.

(c) An increase in the percentage of carbon dioxide, methane, nitrous oxide and chlorofluorocarbons traps the heat causing the temperature of the earth and its surroundings to rise. This is known as global warming.

(d) Oxides of nitrogen form a mixture of smoke and fog known as smog which affects our eyes too.

Question 4

"Air is a mixture." Support this statement citing at least three evidences.

Answer

"Air is a mixture." This statement is supported by following three evidences:

1. The composition of air is not fixed. It varies from place to place and from time to time.
2. The components of air retain their individual properties.
3. No energy exchange occurs when the components of air are mixed with each other.

Question 5

What is air pollution? What are the harmful effects of sulphur dioxide, nitrogen dioxide and hydrogen sulphide present in the air?

Answer

When air contains undesirable substances that are harmful to plants and animals, the air is said to be polluted. The harmful effects of sulphur dioxide, nitrogen dioxide and hydrogen sulphide present in the air are:

1. Sulphur dioxide is highly poisonous gas which causes serious respiratory problems.
2. Nitrogen dioxide form a mixture of smoke and fog known as smog which affects our eyes.
3. Both sulphur dioxide and nitrogen dioxide gases cause acid rain which damages crops and buildings and natural resources like water bodies and patches of land.
4. Hydrogen sulphide is highly obnoxious and causes headache.

Question 6

(a) What are the causes of air pollution?

(b) Suggest five measures to prevent air pollution.

Answer

(a) The causes of air pollution are:

1. Natural process like volcanic eruptions, crop pollination etc.
2. Burning of fuels and fibres.
3. Deforestation
4. Emission of harmful gases from vehicles.
5. Use of chemicals like fertilizers, insecticides and pesticides in agricultural activities.
6. Increase in number of industries.
7. Use of chemical weapons in war.

(b) The five measures to prevent air pollution are:

1. By growing more plants and trees.
2. By installing tall chimneys with filters in factories and power plants.
3. By using internal combustion engines in vehicles.
4. By installing catalytic convertors in vehicles.
5. Avoid burning of paper, garbage, dry leaves and other waste materials.

Exercise II

Question 1

Name:

(a) The most abundant element in the earth's crust.

(b) A chemical called oxygenated water.

(c) A metal highly resistant to rusting.

(d) A mixture of oxygen and carbon dioxide used for artificial respiration.

(e) Two substances from which oxygen can be obtained on a large scale.

(f) An oxide and a carbonate containing oxygen.

(g) Two substances which undergo rapid oxidation.

Answer

(a) Oxygen

(b) Hydrogen peroxide (H₂O₂)

(c) Platinum

(d) Carbogen

(e) Air, water

(f) Sodium oxide (Na₂O), Calcium carbonate (CaCO₃)

(g) Sodium, carbon

Question 2

(a) Taking hydrogen peroxide, how would you prepare oxygen in the laboratory?

(b) What is the role of manganese dioxide in the preparation of oxygen?

(c) Write the balanced chemical equation for the above chemical reaction.

(d) Why is hydrogen peroxide preferred in the preparation of oxygen gas?

(e) Why is oxygen collected by downward displacement of water?

(f) What happens when a glowing splinter is introduced in a jar containing oxygen?

(g) What happens when oxygen gas is passed through alkaline pyrogallol solution?

Answer

(a) Oxygen is prepared from hydrogen peroxide in the laboratory by the following ways-

1. A small quantity of manganese dioxide is taken in a flat bottom flask.
2. Hydrogen peroxide is added drop by drop into the flask by help of thistle funnel as shown in the below figure.

3. Manganese dioxide decomposes hydrogen peroxide very fast and liberates oxygen which passes through the delivery tube and bubbles out through the water in the trough.
4. A gas jar filled with water is inverted over beehive shelf. Oxygen is collected in the jar by downward displacement of water.

(b) Manganese dioxide acts as a catalyst, it decomposes hydrogen peroxide very fast and liberates oxygen.

(c) 2H₂O₂ $\xrightarrow[\text{as catalyst}]{\text{MnO}_2}$ 2H₂O + O₂ [g]

(d) Hydrogen peroxide is preferred in the preparation of oxygen gas because:

1. No heating is required.
2. The rate of evolution of oxygen is moderate and therefore under control.
3. Hydrogen peroxide is a safe chemical.

(e) Oxygen is collected by downward displacement of water because:

1. Oxygen is slightly heavier than air, so it cannot be collected over air.
2. Oxygen is only slightly soluble in water i.e. 0.7% only. So it can be collected over water without fear of excessive dissolution.

(f) When a glowing splinter is introduced in a jar containing oxygen, the glowing splinter rekindles, but the gas does not catch fire.

(g) When oxygen gas is passed through alkaline pyrogallol solution, it turns brown.

Question 3

(a) What happens when (i) mercuric oxide and (ii) potassium nitrate are heated?

(b) Why is potassium chlorate not used for laboratory preparation of oxygen?

Answer

(a)

i. When mercuric oxide is heated, it decomposes to give mercury and oxygen.

2HgO $\xrightarrow{\text{heat}}$ 2Hg + O₂

ii. When potassium nitrate is heated, it decomposes to give potassium nitrite and oxygen.

2KNO₃ $\xrightarrow{\text{heat}}$ 2KNO₂ + O₂

(b) Potassium chlorate is heated to a high temperature to obtain oxygen gas which may cause

1. cracking of glass apparatus being used.
2. accidents and burn injuries. Thus potassium chlorate is not used for laboratory preparation of oxygen gas.

Question 4

What are oxides? Give two examples for each of metallic and non-metallic oxides.

Answer

Oxides are binary compounds formed by the chemical combination of a substance (metal or non-metal) with oxygen.

Two examples of metallic oxides are sodium oxide (Na₂O), calcium oxide (CaO).

Two examples of non-metallic oxides are sulphur dioxide (SO₂), carbon dioxide (CO₂).

Question 5

Name the three types of oxidation processes. In which of these, large amount of heat and light energy are produced?

Answer

The three types of oxidation processes are:

1. Spontaneous oxidation
2. Fast oxidation — Burning/Combustion
3. Slow oxidation — Rusting, Respiration

In Fast oxidation i.e. Burning process large amount of heat and light energy are produced.

Question 6

What do you observe when the following substances are heated and then tested with moist blue and red litmus paper?

(a) Sulphur

(b) Phosphorus

(c) Calcium

(d) Magnesium

Answer

(a) Sulphur burns with a bright bluish flame, giving pungent smell of sulphur dioxide and it turns moist blue litmus paper red.

(b) Phosphorus burns with a dazzling flame producing dense white fumes of phosphorus pentoxide and it turns moist blue litmus paper red.

(c) Calcium burns with a bright brick red flame forming a white solid and it turns moist red litmus paper blue.

(d) Magnesium burns with a bright dazzling light forming white powder of magnesium oxide and it turns moist red litmus paper blue.

Question 7

Complete and balance the following chemical equations.

(a) KNO₃ $\xrightarrow{\text{heat}}$ KNO₂ + ...............

(b) KClO₃ $\xrightarrow{\text{heat}}$ ............... + O₂

(c) HgO $\xrightarrow{\text{heat}}$ ............... + ...............

(d) CaO + H₂O ⟶ ...............

Answer

(a) 2KNO₃ $\xrightarrow{\text{heat}}$ 2KNO₂ + O₂

(b) 2KClO₃ $\xrightarrow{\text{heat}}$ 2KCl + 3O₂

(c) 2HgO $\xrightarrow{\text{heat}}$ 2Hg + O₂

(d) CaO + H₂O ⟶ Ca(OH)₂

Question 8

(a) Give four uses of oxygen.

(b) How is oxygen naturally renewed in air?

Answer

(a) The four uses of oxygen are:

1. Respiration
2. Burning
3. Industrial uses like welding and cutting metals, removing impurities.
4. In medicines like oxygen cylinders for artificial respiration in patients suffering from breathing problems, a mixture of oxygen and nitrous oxide as local anaesthesia.

(b) Oxygen is naturally renewed in air by the process of photosynthesis. Plants use carbon dioxide and water and in presence of sunlight produce glucose and oxygen gas. This oxygen gas is released into air.

Question 9

State two differences between: Rusting and Burning.

Answer

Objective Type Questions

Question 1

Fill in the blanks:

(a) ............... is the most abundant inert gas present in air.

(b) Oxides of sulphur and nitrogen combine with rain water to form ............... and ............... which cause ............... .

(c) ............... and ............... are the most common air pollutants.

(d) ............... discovered the oxygen gas.

(e) Oxygen occupies about ............... of air by volume.

Answer

(a) Argon

(b) sulphurous acid, sulphuric acid, nitrous acid, nitric acid, acid rain

(c) oxides of carbon, dust

(d) Joseph Priestly

(e) 21%

Question 2

Match the following:

Answer

Question 3a

A fuel that releases the least amount of pollutants in the air when used:

1. Sulphur dioxide
2. Chlorofluorocarbon
3. Smoke
4. CNG

Answer

CNG

Reason — CNG is Compressed Natural Gas which is a clean burning fuel and causes very less pollution.

Question 3b

The natural way of adding oxygen to air which involves green plants is called:

1. Photosynthesis
2. Respiration
3. Burning
4. Dissolution

Answer

Photosynthesis

Reason — Oxygen is naturally renewed in air by the process of photosynthesis. Plants use carbon dioxide and water and in presence of sunlight produce glucose and oxygen gas. This oxygen gas is released into air.

Question 3c

Which one of the following is most likely to be corroded?

1. a stainless steel cup-board
2. a galvanized iron bucket
3. an iron hammer
4. a tin plated iron box

Answer

an iron hammer

Reason — Iron gets corroded easily when comes in contact with air and moisture, so iron hammer is most likely to get corroded.