Samacheer Kalvi 8th Science Solutions Chapter 11 Pdf

Samacheer Kalvi 8th Science Solutions Chapter 11 Pdf

Tamilnadu Board Samacheer Kalvi 8th Science Solutions Chapter 11: Tamilnadu State Board Solution Class 8 Science Chapter 11 – Air.

Samacheer Kalvi 8th Science Solutions Chapter 11: Overview


Samacheer Kalvi





Chapter Name


Samacheer Kalvi 8th Science Solutions Chapter 11 Pdf

(I) Choose the best answer.

(1) Which of the following is true about oxygen?

a ) Completely burning gas

b) Partially burning gas

c) Doesn’t support burning

d) Supports burning

(2 ) Aerated water contains

a ) air

b) oxygen

c) carbon dioxide

d) nitrogen

(3) Solvay process is a method to manufacture

a) lime water

b) aerated water

c) distilled water

d) sodium carbonate

(4) Carbon dioxide with water changes

a ) blue litmus to red

b) red litmus to blue

c) blue litmus to yellow

d) doesn’t react with litmus

(5) Which of the following is known as azote ?

a) Oxygen

b) Nitrogen

c) Sulphur

d) Carbon dioxide

(II )Fill in the blanks .

1) Oxygen is called as vital life .

2) Nitrogen is lighter than air.

3) Nitrogen is used as a fertilizer.

4) Dry ice is used as a refrigerant.

5) The process of conversion of iron into hydrated form of oxides is called rusting.

(III ) Match the following.

Nitrogen Respiration in living animals
Oxygen Fertilizer
Carbon dioxide Refrigerator
Dry ice Fire extinguisher


Nitrogen Fertilizer
Oxygen Respiration in living animals
Carbon dioxide Fire


Dry ice Refrigerator

(IV) Answer briefly.

 1 ) Mention the physical properties of oxygen.

The physical properties of oxygen are as follows:

  • Oxygen gas does not possess any colour, odour or taste.
  • It has a low thermal and electrical conductivity.
  • Oxygen gas can dissolve rapidly in cold water.
  • It is more denser when compared to air.
  • It can be transformed into a liquefied state at high pressure and low temperature.
  • It renders support to the process of combustion.

2) List out the uses of nitrogen.

The uses of nitrogen are as follows:

  • The liquefied form of nitrogen can be used as a refrigerant.
  • An inert atmosphere is provided by nitrogen in order to conduct specific chemical reaction.
  • It performs an essential role in the preparation of ammonia which is then transformed into fertilizers and nitric acid.
  • In present times, it is used as an alternative for compressed air that are used in tyres.
  • In high temperature thermometer, it is used to fill up the space above mercury, so that the evaporation of mercury can be decreased to a considerable extent.
  • TNT, nitroglycerin and gun powder are for instance , the various explosives that makes use of nitrogen.
  • It is not only used for the purpose of preserving food but it is also used in the production of stainless steel, decreasing fire hazards and as a portion of gas in incandescent bulbs.

3) Write about the reaction of nitrogen with non metals.

There is an occurrence of reaction of nitrogen with other non- metals such as hydrogen and oxygen for the purpose of forming their corresponding nitrogen compound at a relatively high temperature.

Non – metal + Nitrogen     —–∆——> Nitrogen



3H2+ N2—∆—->2NH2

Hydrogen   Nitrogen             Ammonia

4) What is global warming?

The temperature of the earth’s surface increases in a gradual manner, when there is a rise in the levels of greenhouse gases. When the air pollutants increases to a certain extent , then it paves the way for causation of greenhouse effect, which in turnincreases the temperature of the atmosphereto a moderate extent.  This is known as Global warming.

5) What is dry ice? What are its uses?

Dry ice refers to the solid carbon dioxide ,which is used as a refrigerant. The moisture in the air condenses on the gas due to its severe coldness and thus forms a dense fog which is then used for the purpose of stage shows and creating movie effects.

(V)Answer in detail.

1) What happens when carbon dioxide is passed through lime water? Write the equation for this reaction.

The lime water turns milky, when a limited quantity of CO2 is passed through it because of the formation of calcium carbonate.

The equation for this reaction are as follows:

Ca(OH)2 + CO2  ———–>CaCO3+ H2O

Calcium carbonate

Initially,  the lime water turns milky when an excessive quantity of carbon dioxide is passed through it but because of the formation of calcium hydrogen carbonate , Ca(HCO3 )2,this milkyness also disappears.

2) Name the compounds produced when the following substances  burn in oxygen.

 a ) Carbon                       

b) Sulphur

c) Phosphorus d) Magnesium

e) Iron f) Sodium


a ) Carbon Carbon dioxide (CO2 )
b) Sulphur Sulphur dioxide (SO2 )
c) Phosphorus Phosphorus trioxide

(P2O3 ) or Phosphorus pentoxide

(P2O5 )

d) Magnesium Magnesium Oxide (MgO)
e) Iron Iron Oxide

(Fe2O3 )

f) Sodium Sodium Oxide

( Na2O)

3) How does carbon dioxide react with the following?

a ) Potassium                         b) Lime water

c) Sodium hydroxide


a) When CO2 combines with potassium ,then it leads to the formation of potassium carbonate.

The equation for this reaction are as follows:

4K + 3CO2——->2K2CO3+ C


b) The lime water turns milky, when a limited quantity of CO2 is passed through it because of the formation of calcium carbonate.

The equation for this reaction are as follows:

Ca(OH)2  + CO2  ———–> CaCO3 + H2O

Calcium carbonate

c) Carbon dioxide neutralizes sodium hydroxide in order to form sodium bicarbonate and water.

The equation for this reaction are as follows :

NaOH+ CO2 ———–>NaHCO3 +  H2O

Sodium bicarbonate

4) What are the effects of acid rain? How can we prevent them?

Effects of Acid rain

Acid rain brings about a negative impact on our life in several ways. Some of the effects are as follows:

  • It causes irritation to the human eyes and skin.
  • The germination and growth of seedlings are hindered by it to a considerable extent.
  • The fertility of the soil gets affected by acid rain. It also poses harmful effects to the plants and aquatic animals.
  • Many buildings and bridges tends to corrode due to the occurrence of acid rain.

Preventive measures

If the following measures are taken into consideration , then the effects of acid rain can be controlled to a great extent.

  • The usage of fossil fuels like petrol and diesel should be reduced to a considerable extent.
  • Other fuel options like diesel and petrol should be replaced with CNG (Compressed Natural Gas) . As, no harmful gases are produced by CNG and it also does not have any smoke ,for that reason it is a far better option when compared to other fuels.
  • One should always try to use non -conventional source of energy.
  • The industrial waste should be disposed in a proper and effective manner.

(VI) Higher Order Thinking Questions.

 1 ) Soda bottle bursts sometimes when it is opened during summer. Why?

Soda bottle tends to burstwhen it is opened during summer because soda bottle contains carbon dioxide gas which is dissolved in water under pressure. So as a result of which, there is an expansion of the gas in the bottle and which in turn increases the pressure within the bottle. For this reason, the bottle may tend to burst in summer season.

2) It is said that sleeping beneath the tree during night is not good for health. What is the reason?

During night, it is not advisable to sleep under the tree because trees reverses their role at night, which means they take up oxygen and releases carbon dioxide . So, a person who will sleep beneath the tree will lack sufficient oxygen for breathing which may lead to suffocation and breathing trouble.So for this reason, sleeping under the tree during night is not suitable for health.

3) Why does the fish die when it is taken out of water?

Fish dies when they are  taken out of water because fish contains gills, whose main function is to absorb the oxygen that is dissolved in water.  There is a discontinuation in the supply of oxygen, the moment they are taken out of water. As a result of which , they are unable to breathe and absorb the oxygenthat are contained in the air. Due to this reason, they cannot survive when they are taken out of water.

4) How do astronauts breathe when they go beyond earth’satmosphere?

Astronauts have to carry their own oxygen with them because it is not possible to breathe in space. Energy from the solar arrays facilitates the splitting of hydrogen and oxygen from water and this energy can be used in order to make their own oxygen. So in this way, astronauts continues their breathing process when they go beyond earth’s atmosphere.

Updated: November 26, 2021 — 4:34 pm

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