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Science [2 Mark Questions]

Air. · Tamil Nadu Board STD 8 (Tamil - English Medium). 9 questions.

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[2 Mark Questions]

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9 questions · timed · auto-graded

Question 12 Marks
  1. Explain the physical properties of carbon dioxide.
  2. Write the preventive measures to control the effect of global warming
Answer
1. Physical properties of carbon dioxide:
  • Carbon dioxide is a colorless and odorless gas.
  • It is heavier than air.
  • It does not support combustion.
  • It is fairly soluble in water and turns blue litmus slightly red. So it is acidic in nature.
  • It can easily be liquefied under high pressure and can also be solidified. This
  • solid form of $CO _2$ is called dry ice which undergoes sublimation.
2. Preventive measures:
  • Reduction in the use of fossil fuels.
  • Controlling deforestation.
  • Restricting the use of CFCs.
  • Planting more trees.
  • Reducing, reusing and recycling resources.
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Question 22 Marks
Write the uses of nitrogen.
Answer
Uses of Nitrogen:
  1. Liquid nitrogen is used as a refrigerant.
  2. It provides an inert atmosphere for conducting certain chemical reactions.
  3. It is used to prepare ammonia (by Haber’s process) which is then converted into fertilizers and nitric acid.
  4. It is used for inflating tyres of vehicles.
  5. It is used for filling the space above mercury in high temperature thermometer to reduce the evaporation of mercury.
  6. Many explosives such as TNT (Trinitrotoluene), nitroglycerin and gun powder contain nitrogen.
  7. It is used for the preservation of fresh foods, manufacturing of stainless steel, reducing fire hazards and as part of the gas in incandescent light bulbs.
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Question 32 Marks
Write the physical properties of nitrogen.
Answer
  1. Physical properties of nitrogen
  2. It is a colorless, tasteless and odorless gas.
  3. It is slightly lighter than air.
  4. It is slightly soluble in water.
  5. Nitrogen becomes a liquid at low temperature and looks like water. When it freezes, it becomes a white solid.
  6. It is neutral to litmus like oxygen.
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Question 42 Marks
Explain the uses of oxygen.
Answer
Uses of oxygen:
  1. It is used as oxy – acetylene light for cutting and welding metals.
  2. It is used to remove carbon impurities from steel.
  3. Plants and animals use oxygen from the air for respiration.
  4. It is used to oxidize rocket fuel.
  5. It is used for artificial respiration by scuba divers, mountaineers, astronauts, patients etc.
  6. Mixed with powdered charcoal it is used as explosives.
  7. It is used in the synthesis of methanol and ammonia.
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Question 52 Marks
Why does the fish die when it is taken out of water?
Answer
  1. Gills are richly supplied with blood capillaries and can readily absorb the oxygen dissolved in water.
  2. When fishes are taken out of the water, the supply of oxygen to the fishes is cut as the fishes cannot absorb and breathe using the oxygen present in the atmosphere.
  3. Hence they die, when it is taken out of water.
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Question 62 Marks
Soda bottle bursts sometimes when it is opened during summer. Why?
Answer
  1. In a soda bottle, carbon dioxide gas is dissolved in water under pressure.
  2. The gas in the bottle expands.
  3. Hence, the pressure inside the bottle increases.
  4. Thus the bottle may burst in hot summer.
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Question 72 Marks
What happens when carbon dioxide is passed through lime water? Write the equation for this reaction.
Answer
When a limited amount of CO2 is passed through lime water, it turns milky due to the formation of insoluble calcium carbonate.
Ca(OH)2 + CO2 → CaCO3 + H2O
When an excess amount of CO2 is passed through lime water, it first turns milky and the milkyness disappears due to the formation of soluble calcium hydrogen carbonate, Ca(HCO3)2.
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Question 82 Marks
Write about the reaction of nitrogen with non metals.
Answer
Nitrogen reacts with non-metals like hydrogen, oxygen, etc, at high temperatures to form their corresponding nitrogen compounds.
Non-metal + Nitrogen [Math Processing Error] Nitrogen compound

Example:

Write about the reaction of nitrogen with non-metals.

3H2      +        N2          →     2NH3  

Hydrogen    Nitrogen         Ammonia

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Question 92 Marks
List out the uses of nitrogen.
Answer
Uses of nitrogen:
  1. Liquid nitrogen is used as a refrigerant.
  2. It provides an inert atmosphere for conducting certain chemical reactions.
  3. It is used to prepare ammonia (by Haber’s process) which is then converted into fertilizers and nitric acid.
  4. It is used for inflating the tires of vehicles.
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[2 Mark Questions] - Science STD 8 Questions - Vidyadip