Living Science Chemistry Class 7 ICSE Solutions Chapter 3 Air

ICSE Living Science Chemistry for Class 7 Solutions Chapter 3 Air

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Answer these questions
Question 1.
How did Priestley prepare oxygen ?
Answer:
Priestley by prepared oxygen by heating mercury (II) oxide using the infra red rays of the sun.

Question 2.
Which gas is produced on heating sodium nitrate ?
Answer:

Question 3.
Which catalyst is used to prepare oxygen from hydrogen peroxide ?
Answer:
Manganese dioxide

Question 4.
What type of oxidation occurs in the burning of phosphorus ?
Answer:
Spontaneous oxidation

Question 5.
What happenes when magnesium reacts with oxygen ?
Answer:
Magnesium reacts with oxygen to undergo oxidation and forms magnesium oxide

A. Tick the most appropriate answer.

Question 1.
Which among the following is not an example of oxidation?
a. Formation of metal oxides
b. Rusting
c. Burning of fuels
d. Photosynthesis
Answer:
d. Photosìthesis

Question 2.
Rust is
a. iron(Il) oxide
b. iron (II) sulphate
c. hydrated iron (III) oxide
d. iron(Ill) sulpbatc
Answer:
c. hydrated iron (Ill) oxide

Question 3.
Galvanizing is the process of coating iron with a layer of molten
a. zinc
b. copper
c. tin
d. chromium
Answer:
a. zinc

Question 4.
Tin plating is the process of coating a metal with a layer of
a. aluminium
b. zinc
c. copper
d. tin
Answer:
d.tin

Question 5.
Dry iceis
a. solid carbon dioxide
b. supercooled ice
c. crushed ice
d. solid oxygen
Answer:
a. solid carbon dioxide

Question 6.
Which of the following contributes (s) to the greenhouse effect?
a. Methane
c. ChlorofluorocarbOfls
b. Carbon dioxide
d. All of these
Answer:
d. All of these

Question 7.
Melting of polar ice caps is associated with
a. global warming
b. ozone depletion
c. acid rain
d. oxidation
Answer:
a. global warming

Question 8.
Which inert gas is used in flashlamps for photography ?
a. Argon
b. Neon
c. Helium
d. Krypton
Answer:
d. Krypton

B. Fill in the blanks.

Question 1.
The blanket of air around the earth is called the ………..
Answer:
The blanket of air around the earth is called the atmosphere.

Question 2
…………. and ………… mixed with rainwater cause acid rain
Answer:
Oxides of nitrogen and sulphur dioxide mixed with rainwater cause acid rain

Question 3.
Due to the presence of the ozone layer, the harmful ………….. rays from the sun cannot reach the earth directly.
Answer:
Due to the presence of the ozone layer, the harmful ultraviolet rays from the sun cannot reach the earth directly.

Question 4.
Automobile emissions can be checked by installing a device called ………….
Answer:
Automobile emissions can be checked by installing a device called catalytic convertor.

Question 5.
In the laboratory preparation of oxygen, ………….. is used as a catalyst.
Answer:
In the laboratory preparation of oxygen, manganese dioxide is used as a catalyst.

Question 6.
…………. gas is produced when metal carbonates are heated
Answer:
Carbon dioxide gas is produced when metal carbonates are heated

Question 7.
Carbon dioxide turns lime water ………….. due to the formation of
Answer:
Carbon dioxide turns lime water milky due to the formation of insoluble calcium carbonate.

Question 8.
gas is used to existinguish a fire.
Answer:
Carbon dioxide gas is used to existinguish a fire.

Question 9.
gas is used in packing food items.
Answer:
Nitrogen gas is used in packing food items.

Question 10.
gas is used for filling balloons for weather studies.
Answer:
Helium gas is used for filling balloons for weather studies.

C. Match the following.

Column A	Column B
1.Chlorofluorocarbons	a. mixture of sodium bicarbonate and tartaric acid
2.Trinitrotoluene	b. calcium hydroxide solution
3. Baking powder	c. explosive
4. Lime water	d. carbonic acid
5. Oxy-acetylene flame	e. LOX
6. Liquid oxygen	f. sodium bicarbonate + sulphuric acid
7.Soda-acid fire extinguisher	g. used for cutting and welding metals
8. Poisonous gas	h. global warming
9. Melting of polar ice caps	i. depletion of ozone layer
	j. carbon monoxide

Answer:

Column A	Column B
1.Chlorofluorocarbons	i. depletion of ozone layer
2.Trinitrotoluene	c. explosive
3. Baking powder	a. mixture of sodium bicarbonate and tartaric acid
4. Lime water	b. calcium hydroxide solution
5. Oxy-acetylene flame	g. used for cutting and welding metals
6. Liquid oxygen	e. LOX
7.Soda-acid fire extinguisher	f. sodium bicarbonate + sulphuric acid
8. Poisonous gas	j. carbon monoxide
9. Melting of polar ice caps	h. global warming

D. State if the following statements are true or false. Correct the statement if it is false.

Question 1.
Asbestos fibre can cause a disease called silicosis.
Answer:
True

Question 2.
Potassium nitrate on heating decomposes into potassium nitrite and oxygen gas.
Answer:
False. Potassium nitrate on heating decomposes into potassium nitrite and nitrogen gas.

Question 3.
Rusting is a rapid oxidation reaction.
Answer:
False. Rusting is a slow oxidation reaction.

Question 4.
Carbon dioxide turns moist red litmus blue
Answer:
False. Carbon dioxide turns moist blue litmus red.

Question 5.
Carbon dioxide is heavier than air.
Answer:
True

Question 6.
Nitrogen reacts with metals to form metal nitrides.
Answer:
True

Question 7.
Helium gas is used for filling electric bulbs.
Answer:
False. Argon gas is used for filling electric bulbs.

E. Name the following.

Question 1.
A catalyst used in the laboratory preparation of oxygen from hydrogen peroxide.
Answer:
Manganese dioxide

Question 2.
The process of coating zinc on the surface of iron to prevent rusting.
Answer:
Galvanization

Question 3.
A mixture of oxygen and carbon dioxide used to stimulate breathing
Answer:
Carbogen

Question 4.
The compound produced by the Haber process
Answer:
Ammonia (NH3)

Question 5.
A gas used in hospitals for preserving blood, tissues, etc.
Answer:
Nitrogen

Question 6.
A gaseous mixture used by deep-sea divers for breathing.
Answer:
Oxygen – Helium mixture

Question 7.
The noble gas used in advertisement signs
Answer:
Neon

F. Answer the following in short.

Question 1.
Name the two acids present in acid rain.
Answer:
Nitric acid and sulphuric acid.

Question 2.
What happens when red lead oxide is heated ?
Answer:
When red lead oxide is heated, lead monoxide is formed along with oxygen gas. Oxygen gas can be prepared by this method.

Question 3.
State the use of manganese dioxide in the laboratory preparation of oxygen from hydrogen peroxide.
Answer:
Manganese dioxide is used as a catalyst in the laboratory preparation of oxygen from hydrogen peroxide.

Question 4.
What is rust ? State two important conditions necessary for rusting.
Answer:
When an iron object is exposed to moist air, its surface gets covered with a reddish brown powder called rust. Two conditions necessary for rusting to take place :
(i) Presence of air (or oxygen)
(b) Presence of water (or moisture).

Question 5.
What is meant by galvanization ?
Answer:
Galvanization is a process that involves coating iron with a thin layer of zinc to prevent rusting of iron. As zinc is more reactive than iron, it reacts with oxygen in the presence of moisture and prevents iron from msting. Iron coated with zinc is called galvanized iron (GI).

Question 6
What is dry ice ? What is it used for ?
Answer:
Dry ice is solid carbon dioxide which gives -40°C, sublimes and is non-poisonous. It is used as a refrigerant for preserving food items such as vegetables, fruits and meat.

Question 7.
What are the chemicals used in a soda-acid fire extinguisher ?
Answer:
Sodium bicarbonate solution and dilute sulphuric acid.

Question 8.
What is a greenhouse gas ?
Answer:
Green house effect is a natural effect occurring in the atmosphere because of centrain gases that absorb heat energy radiated from the earth’s surface and reradiate it back to the earth’s surface. The major green house gases are carbon- dioxide, methane and water vapour.

Question 9.
What is global warming ?
Answer:
The phenomenon of increasing air temperature near the earth’s surface is called global warming. The increasing carbon dioxide level in the atmosphere has led to excessive heating of the earth’s surface.

Question 10.
What is the use of liquid nitrogen in hospitals ?
Answer:
Liquid nitrogen is used in hospitals for storing and preserving blood, tissues, etc as it provides a very low temperature.

Question 11.
What is nitrogen fixation ?
Answer:
The process of converting free nitrogen of the atmosphere into nitrogen compounds such as ammonia and nitrates is called nitrogen fixation. In nature, it is done by nitrogen-fixing bacteria in soil or root nodules of legumes. Lightning also converts nitrogen gas to nitrate compounds.

G Answer the following in detail.

Question 1.
What is air pollution ? What are the harmful effects of the following pollutants ?
a. Carbon monoxide
b. Sulphur dioxide
c. Nitrogen oxide
Answer:
Air pollution means the addition of undesired substances to the natural air like gases, dust, smoke, etc which are harmful to plants animal life and environment. Substances that cause pollution are called pollutants.

a. Carbon monoxide – Carbon monoxide is a highly poisonous gas. When inhaled, it combines with the haemoglobin present in blood to form a stable compound called carboxyhaemoglobin and thus lowers the oxygen-carrying capacity of blood. Breathing in carbon-monoxide causes headache, dizziness and can even lead to death.

b. Sulphur dioxide – Sulphur dioxide is poisonous and affects our lungs. It may cause eye and throat irritation. It also combines with water vapour in the air to form sulphuric acid which fells down with rain causing acid rain, damaging building, aquatic life, plants, soil, animals, etc. Sulphur dioxide may also lead to heart problems and birth defects.

c. Nitrogen oxide – Nitrogen oxide reacts with water vapour present in the air to form nitric acid which is a component of acid rain. Acid rain damages buildings, plant and animal life, soil, etc. Oxides of nitrogen also form smog, which affects our lungs and eyes. Nitrogen oxides can also lead to heart problems and cancer.

Question 2.
Suggest any five ways to prevent air pollution.
Answer:
Ways to prevent air pollution :

1. Use of fossil fuels should be reduced. Clean fuels such as solar energy and wind energy should be used in place of conventional fossil fuels like coal and petroleum.
2. Pollution from automobile emissions can be reduced by installing a special device called catalytic converter.
3. Industries must release gas into the air only after removing solid particles (particulate matter) and poisonous gases using device called electrostatic precipitator.
4. Industries should be located away from residential areas.
5. At an individual level, we should use public transport or carpooling or bicycles, should avoid burning of crackers and plant more trees.

Question 3.
Describe the laboratory preparation of oxygen from hydrogen peroxide with a neat labelled diagram. Also, write the balanced equation for the reaction involved.
Answer:
Oxygen gas can be prepared in the laboratory by the decomposition of hydrogen peroxide using manganese dioxide as a catalyst.

Aim : To prepare oxygen from hydrogen peroxide manganese dioxide as a catalyst.
Materials required : A flat-bottom flask, a two-holed rubber stopper, a thistle funnel with a stopper, a delivery tube, a beehive shelf, a gas jar, a trough containing water, hydrogen peroxide, manganese dioxide.

Procedure :

1. Take some manganese dioxide in a flat-bottom flask.
2. Set up die apparatus as shown in the figure.
3. Add hydrogen peroxide drop by drop through the thistle funnel.

Observation :
As hydrogen peroxide drips onto manganese dioxide, a brisk effervescence takes place due to the evolution of oxygen gas

Collection of oxygen gas :
Oxygen gas is collected by the downward displacement of water because it is very slightly soluble in water. Again, it cannot be collected over air since it almost as heavy as air.

Question 4.
State any four ways for prevention of rusting.
Answer:
Ways to prevent rusting of iron :

1. Painting with red lead – Painting the iron surface with red lead does not allow it to come in contact with moist air and thus prevent rusting. For example, railings, lamp posts and window panes are painted to prevent them from rusting.
2. Using grease or oil – Metallic tools and machine parts may be coated with a thin layer of grease or oil to prevent them from rusting.
3. Galvanization – It involves coating iron with a thin layer of zinc to prevent iron from rusting. Articles that are exposed to
   extreme moiture such as roof sheets, tubs, buckets and water pipes are protected from rusting by galvanization.
4. Alloying – Iron can be alloyed with chromium and nickel to form stainless steel which is lustrous and corrosion – resistant and is used to make cutting and surgical instruments, utensils, etc.
5. Tin plating – Iron is coated with a protective layer of tin. Tin is non-toxic and less reactive than iron. Food cans are coated with tin prevent them from rusting.

Question 5.
Describe soda-acid fire extinguisher.
Answer:
Soda-acid fire extinguisher consists of a container filled with sodium bicarbonate solution. Sulphuric acid is also kept inside the container in a sealed glass bottle. To use the extinguisher, the glass bottle containing the acid is broken by striking the plunger. Sodium bicarbonate and sulphuric acid react to form carbon-dioxide, which rushes out through the nozzle. Carbon dioxide is directed towards the fire and it cuts off the supply of air by forming a layer on the fire, and finally the fire gets extinguished.

Question 6.
What is greenhouse effect ? How is it related to global warming ?
Answer:
The greenhouse effect is a natural process in which greenhouse gases trap heat radiated from the earth’s surface and reradiate it back to the earth’s surface. The major green house gases are carbon dioxide, methane and water vapour. The green house effect keeps the earth pleasantly warm. However, we are producing too many greenhouse gases that absorb more heat and warm the earth too much. Carbon dioxide is the most important greenhouse gas.

Due to excessive burning of fossil fuels and other carbon containing, fuels, and large scale deforestation, there has been an excessive release of carbon dioxide into the atmosphere. The increasing carbon dioxide level in the atmosphere has led to excessive heating of the earth’s surface. This phenomenon of increasing air temperatures near the earth’s surface is called global warming.

Question 7.
Describe the laboratory preparation of nitrogen.
Answer:
Nitrogen is prepared in the laboratory by the action of heat on a mixture of ammonium chloride and sodium nitrite. A saturated solution containing equal amounts of ammonium chloride (“NH₄Cl) and sodium nitrite (NaNO₂) is taken in a round bottom flask and gently heated. On gently heating the reactants in the flask, a slow evolution of nitrogen gas takes place.

Question 8.
Write five uses of nitrogen.
Answer:
Uses of nitrogen :

1. Synthesis of proteins by plants – Plants directly or indirectly use nitrogen from the air for making proteins.
2. In the manufacture of ammonia – Nitrogen is used in the manufacture of ammonia by the Haber process.
3. In the manufacture of explosives – Most of the chemical explosives contain nitrogen, for example, trinitrotoluene (TNT) and nitroglycerine.
4. In hospitals – Liquid nitrogen in used in hospitals for storing and preserving blood, tissues, etc. as it provides a very low temperature.
5. In the food industry – Because of its inert nature, nitrogen is used in food packaging. The containers used for storing food stuff are flushed with nitrogen to remove oxygen before they are sealed. It stops bacterial growth chances and preserve food. Liquid nitrogen is also used for preserving foods such as cakes and pastries.
6. In the manufacture of fertilizers – such as urea, ammonium sulphate, ammonium phosphate.

H. Give reasons for the following.

Question 1.
Oxygen is collected by the downward displacement of water.
Answer:
Oxygen is collected by the downward displacement of water as oxygen is very slightly soluble in water and it cannot be collected over air since it is almost as heavy as air. So it displaces water downwards and the oxygen gas gets collected above water in jar.

Question 2.
Dilute sulphuric acid is not used for the preparation of carbon dioxide from marble chips.
Answer:
It is so because dilute sulphuric acid reacts with calcium carbonate (marble chips) to form a coating of insoluble calcium sulphate (CuSO₄) on the marble chips and thereby preventing any further reaction.

Question 3.
Solid carbon dioxide is used for the refrigeration of food.
Answer:
Solid carbon dioxide (dry ice) is used for the refrigeration of
food as it gives – 40°C temperature, sublimes and is non- poisonous.

Question 4.
Carbon dioxide gas is used in fire extingushers.
Answer:
As carbon dioxide is neither combustible nor a supporter of combustion, it is used in fire extinguishers to put out fire. Being heavier than air, it settles and forms a blanket over the fire and thus cuts off the supply of oxygen to put off the fire.

Question 5.
Nitrogen is used in food packaging.
Answer:
Because of its inert nature, nitrogen is used in food packaging. The containers used for storing foodstuffs are flushed with nitrogen to remove oxygen before they are sealed. The absence of oxygen does not allow bacterial growth. Thus, food stufs remain fresh for a long time.

I. What do you observe in the following cases 

Question 1.
When oxygen is brought in contact with nitrogen oxide Ans. The nitrogen oxide (NO) reacts very quickly with oxygen to
form nitrogen dioxide.

Question 2.
When blue litmus is introduced into a jar containing carbon dioxide
Answer:
Carbon dioxide turns blue litmus red.

Question 3.
When a burning splinter is introduced in a jar containing carbon dioxide
Answer:
The burning splinter gets extinguished as carbon dioxide does not support combustion.

Question 4.
When carbon dioxide is passed through lime water first in a small amount and then in excess
Answer:
When carbon dioxide is passed through lime water in a small amount, it turns milky due to the formation of insoluble calcium carbonate.

If excess of carbon dioxide is passed through the milky suspension, the solution becomes clear due to the formation of soluble calcium bicarbonate.

J. Write the balanced equations for the following.

Question 1.
Red lead oxide, Pb304, is heated
Answer:

Question 2.
Potassium nitrate is strongly heated
Answer:

Question 3.
Phosphorus is burnt in oxygen
Answer:

Question 4.
Formation of rust
Answer:

Question 5.
Sodium carbonate reacts with dil. sulphuric acid
Answer:

Question 6.
Sodium hydroxide reacts with carbon dioxide
Answer:

K. Draw labelled diagrams of the following.

Question 1.
Oxygen cycle
Answer:

Question 2.
carbon cycle
Answer:

Question 3.
Nitrogen cycle
Answer:

Living Science Chemistry Class 7 ICSE Solutions