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Chapter: 07. Air And Atmosphere

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IN-TEXT ACTIVITIES QUESTIONS

Activity 0
Question: Name a gas that supports combustion.
Answer: Oxygen gas (
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).
Activity 2
Question: Name the substances formed when
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reacts with limewater.
Answer: Calcium carbonate (
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) and water (
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).
Activity 4
Question: Name the process which is used for collecting gases that are insoluble or slightly soluble in water.
Answer: Downward displacement of water.
Activity 6 (Tests for Oxygen)
Question: Name the non-combustible gas in the above experiment.
Answer: Oxygen (Oxygen itself is non-combustible as it does not burn or catch fire, but it is a strong supporter of combustion).
Activity 6 (Burning of Elements in Oxygen)
Question: What type of oxides are formed when non-metals react with oxygen?
Answer: Non-metallic oxides, which are acidic in nature.
Activity 7
Question: What is the nature of oxides formed, when metals are burnt in the presence of oxygen?
Answer: Metallic oxides, which are basic in nature.
Activity 8
Question: Why does magnesium gain weight when burnt in presence of air?
Answer: When magnesium burns, it chemically combines with oxygen in the air to form magnesium oxide (
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). The added weight of the oxygen causes the product to weigh more than the original magnesium metal.
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EXERCISE FOR REVISION (PAGES 184-185)

Tick (✓) the correct options.
Question 1: Which of the following is not representing the correct percentage of components of air?
Answer: (b) Oxygen: 26%
Question 2: Which of the following was observed by Antoine Lavoisier during his experiment?
Answer: (b) One-fifth portion of air was active air.
Question 3: When carbon dioxide is passed through the limewater, the limewater turns milky due to the formation of a white precipitate of
Answer: (​c​) calcium carbonate
Question 4: The amount of water vapour present in air during the rainy season is more than that in summers due to
Answer: (b) high humidity
Question 5: Which of the following is not a property of nitrogen?
Answer: (d) highly soluble in water
Question 6: Nitrogen is used
Answer: (d) all of these
Question 7: Which of the following does not support the statement ‘air is a mixture of gases’?
Answer: (b) It can be represented by a fixed formula.
Question 8: Which of the following shows the correct sequence of steps in the nitrogen cycle?
Answer: (​c​) (iv)(iii)(ii)(v)(i)
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EXERCISE FOR REVISION (PAGE 186)

A. Tick (✓) the correct options.
Question 1: Which of the following is required by all living organisms for the breakdown of digested food to get energy?
Answer: (b) oxygen
Question 2: Which of the following compounds does not contain oxygen?
Answer: (d) ammonia
Question 3: Which of the following gases boils at
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during the fractional distillation of liquid air?
Answer: (a) nitrogen
Question 4: Which of the following compounds does not yield oxygen gas?
Answer: (b) ammonia
Question 5: When oxygen gas is passed through alkaline pyrogallol solution, the solution turns
Answer: (​c​) brown
B. Assertion-Reason based Question.
Question 1:
Assertion: Oxygen is a non-combustible gas.
Reason: Oxygen is a supporter of combustion.
Answer: (b) Both A and R are true but R is not the correct explanation of the assertion.
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EXERCISE FOR REVISION (PAGE 189)

A. Tick (✓) the correct options.
Question 1: Which of the following is formed when carbon burns in insufficient amount of oxygen?
Answer: (b) carbon monoxide
Question 2: Metals burn in oxygen to form ________________________ in nature.
Answer: (a) metal oxides that are basic
Question 3: Lead sulphide burns in oxygen to produce
Answer: (a) lead oxide and sulphur dioxide
Question 4: Which of the following is/are example(s) of slow oxidation?
Answer: (d) both (b) and (​c​)
Question 5: Rusting does not take place in the presence of
Answer: (​c​) carbon dioxide (Note: Technically, rusting does not take place in the absence of oxygen and water, making (d) correct if “presence of” is a typo for “absence of.” If read literally, rusting can occur perfectly fine without carbon dioxide, though carbon dioxide accelerates it).
B. Match the following:
Question: Match Column A with Column B.
Liquid oxygen
Oxyacetylene flame
Calcium
Mixture of oxygen and nitrous oxide
Rust
Answer:
➔ (​c​) propellant fuel in rockets
➔ (e) cutting and welding of metals
➔ (d) bright brick red flame
➔ (b) local anaesthesia in dentistry
➔ (a) hydrated iron oxide
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EXERCISE FOR REVISION (PAGE 191)

A. Tick (✓) the correct options.
Question 1: Baking powder is used to make cakes and bread soft as it releases
Answer: (a) carbon dioxide
Question 2: Which of the following gases is filled in electric bulbs to prevent reaction of tungsten filament with oxygen?
Answer: (a) argon
Question 3: The amount of water vapour present in air is called
Answer: (b) humidity
Question 4: Which of the following causes ozone depletion and global warming?
Answer: (​c​) chlorofluorocarbons
Question 5: Which of the following gases is not responsible for causing acid rain?
Answer: (d) oxygen
B. Assertion-Reason based Questions.
Question 1:
Assertion: Dust particles are minute soil particles present in air.
Reason: They help in the condensation of water vapour.
Answer: (b) Both A and R are true but R is not the correct explanation of the assertion.
Question 2:
Assertion: Air is one of the most important thing necessary for life.
Reason: All living organism breathe in air.
Answer: (a) Both A and R are true and R is the correct explanation of the assertion.
C. Complete the following reactions.
Question 1:
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Answer:
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Question 2:
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Answer:
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Question 3:
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Answer:
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Question 4:
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Answer:
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FLOWCHART FOR REVISION (PAGE 192)

Question: Fill in the blanks in the “Air Pollution” and “Air Composition” Flowchart.
Answer:
Air Composition Blanks:
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Nitrogen
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Carbon dioxide
Rusting Prevention:
Applying paint, oil, grease, and galvanisation prevents the metal from coming in contact with moisture and air (oxygen).
Prevention of Air Pollution:
Can be prevented by: Using CNG, using catalytic converters, and growing trees.
Harmful Effects of Polluted Air:
Causes: Acid rain.
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COMPETENCY BASED DISCUSSION: AIR AND ITS COMPOSITION

A. Short Answer Questions:
Question 1: What is the percentage of the different components present in air?
Answer: The approximate atmospheric percentages of components in dry air are:
Nitrogen:
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Oxygen:
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Argon (and other inert gases):
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Carbon dioxide:
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Water vapour, dust particles, and impurities: Variable percentages.
Question 2: Give two properties each of nitrogen and oxygen.
Answer:
Nitrogen properties:
It is a colourless, odourless, tasteless, and non-poisonous gas.
It is non-combustible and does not support combustion.
Oxygen properties:
It supports combustion (is a strong supporter of burning) though it is non-combustible itself.
It is neutral to indicators (does not change the colour of moist blue or red litmus papers).
Question 3: What is the importance of nitrogen for plants and animals?
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