WBBSE Class 8 Science Solutions Chapter 3 Know About Some Common Gases

Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 3 Know About Some Common Gases offer valuable context and analysis.

WBBSE Class 8 Science Chapter 3 Question Answer – Know About Some Common Gases

Hands-on Activity :

Answer (See Text-book, page-124)

Answer:

Answer (See Text-book, page-125)

Fill up the blanks (See Text-book, page-131-132)
Answer :
A. 1. Zn + dilute H₂ SO₄ → ZnSO₄ + H₂
2. Mg + dilute HCl → MgCl₂ + H₂
3. Fe + dilute H₂ SO₄ → Fe₂(SO₄)₃ + H₂
4. Al + dilute HCl → Al₂ Cl₂ + H₂

B. 1. Na + H₂ O (cold water) → NaO + H₂
2. Ca + H₂ O (cold water) → CaO + H₂
3. Mg + H₂ O (boiling water) → MgO + H₂
4. Al + H₂ O (boiling water) → Al(OH)₂ + H₂
5. (red hot) Fe + H₂ O(. steam) → Fe₂ O₃ + H₂

C. 1. Zn + NaOH (concentrated solution) → Na₂ ZnO₂ + H₂
2. Al + NaOH (concentrated solution) + H₂ O → NaAlO₂ + H₂
Si + 2 NaOH + H₂O = Na₃ SiO₃ + 2 H₂

D. Water acidified with sulphuric acid (H₂O) → O₂ + H₂
E. CaH₂ + 2H₂O → Ca(OH)₂ + H₂
LiH + H₂O → LiOH + H₂

Class 8 Science Chapter 3 Question Answer West Bengal Board – Know About Some Common Gases

Multiple Choice Questions & Answers : (1 mark for each question)

Question 1.
Catalyst enzyme breaks down hydrogen peroxide into-
i) oxygen
ii) hydrogen
iii) water and oxygen
iv) water and hydrogen
Answer:
iii) water and oxygen

Question 2.
Number of isotopes in oxygen-
i) three
ii) four
iii) two
iv) five
Answer:
i) three

Question 3.
Freczing point of liquid oxygen is–
i) -183° C
ii) -100° C
iii) -118° C
iv) -218° C
Ans:
iv) -218° C

Question 4.
Oxygen is-
i) colourless
ii) odourless
iii) tasteless
iv) all of the above
Answer:
iv) all of the above

Question 5.
Alkaline potassium pyrogallate solution absorbs oxygen and turns-
i) white
ii) brown
iii) red
iv) green
Answer:
ii) brown

Question 6.
Water is made up of –
i) hydrogen
ii) oxygen
iii) hydrogen and oxygen
Answer:
iii) hydrogen and oxygen

Question 7.
Which of the following is true-
i) hydrogen is the lightest gas
ii) hydrogen is heavier than air
iii) oxygen is lighter than air
iv) hydroge is equal to air in weight
Answer:
i) hydrogen is the lightest gas

Question 8.
Which of the following is not fertilizer?
i) urea
ii) ammonium sulphate
iii) ammonium nitrate
iv) atomic oxygen
Answer:
iv) atomic oxygen

Question 9.
Which of the following is chemical propertiy of hydrogen?
i) not inflammable
ii) inflammable
iii) formation of oxide
iv) not diatomic
Answer:
ii) inflammable

Question 10.
Which of the following material is required for preparation of hydrogen gas?
i) manganese dioxide
ii) solution of hydrogen peroxide
iii) impure zine granules
iv) pure zinc granules
Answer:
iii) impure zine granules

State whetherTrue or False : (1 mark for each question)

1. Oxyzen is slightly heavier than air:
2. Atomic oxygen is a powerful oxidizing agent.
3. Hydrogen is indispensable in manufacturing nitric acid.
4. Oxygen is completely soluble in water.
5. Oxygen can combine directly with most of the metals and non-metals.
6. Hydrogen is heavier than air.
7. Hydrogen is used in production of ammonia.
8. Hydrogen gas does not help in burning.
9. A woulfe bottle is necessary for preparation of oxygen.
10. Manganese dioxide is required for preparation of hydrogen.
Answer:
1. true
2. true
3. fa’se
4. false
5. truc
6. false
7. true
8. true
9. false
10. false

Fill in the blanks : (1 mark for each question)

1. Hydrogen is necessary in many ___ industries.
2. The industrial world gets its requirement of oxygen from _____.
3. Oxygen-dependent processes do generate more ______ but there are some disadvantages.
a. Aluminium reacts with oxygen and produce ______.
5. At normal or low temperature Au, Ag can absorb______.
6. Delute solution of hydrogen is required for preparation of ______.
7. Colourless nitric oxide gas is oxidized to brown _______ in contact with oxygen.
8. The main use of hydrogen is in the production of _____.
9. Air is about 14.4 times havier than ______.
10. Hydrogen does not help in burning but it is ______.
11. Platinum can absorb ______ gas at normal temperature.
Answer:
1. chemical
2. air
3. energy
4. aluminium oxide
5. oxygen
6. oxygen
7. nitrogen dioxide
8. ammonia
9. hydrogen
10. inflammable
11. hydrogen
12. chemical

Match the following : (1 mark for each question)

a) Match the column A with column B.

Column A	Column B
a) Oxygen is slightly	i) manufacturing nitric acid.
b) Atomic oxygen is a powerful	ii) from vegetable oils.
c) Alkaline potassium pyrogallate solution	iii) insoluble in water.
d) Oxygen is indespensable in	iv) oxidizing agent.
c) hydrogen is used to produce edible fats	v) is 218°C
f) Hydrogen is almost	vi) hydrogen is colourless and tasteless.
g) Freezing point of liquid oxygen	vii) heavier than air:
h) Oxygen is	viii) react with oxygen.
i) Under normal coditions	ix) absorbs oxygen and turns blue.
j) Aluminium and rine	x) not inflammable.

Answer:
a) Oxygen is slightly heavier than air.
b) Atomic oxygen is a powerful oxidizing agent.
c) Alkaline potassium pyrogallate solution absorbs oxygen and tums blue.
d) Oxygen is indespensable in manufacturing nitric acid.
e) hydrogen is used to produce sdible fats from vegetable oils.
1) Hydrogen is almost insoluble in water.
g) Freezing point of liquid oxygen is -218° C.
h) Oxygen is not inflammable.
i) Under normal coditions hydrogen is colourless and tasteless.
j) Aluminium and zinc react with oxygen.

Very Short Questions & Answers : (1 mark for each question)

Question 1.
What does the decomposition of H₂ O₂ produce?
Answer:
Water and oxygen.

Question 2.
What is the chemical symbol of hydrogen?
Answer:
H₂

Question 3.
What is the specific gravity of hydrogen?
Answer:
It is the lightest of all gases with a specific gravity of 0.0695 .

Question 4.
How is hydrogen detected?
Answer:
It can be detected by chemical analysis.

Question 5.
Is hydrogen water soluble?
Answer:
No.

Question 6.
What is the specific gravity of oxygen?
Answer:
Specific gravity of oxygen is 1.105

Question 7.
What is the chemical symbol of oxygen?
Answer:
O₂

Question 8.
Is oxygen flamable?
Answer:
No. Oxygen alone will not burn.

Question 9.
When the oxygen level in air considered to he dangerous?
Answer:
When oxygen level falls below 16 %.

Question 10.
What element in the air is essential for life?
Answer:
Oxygen.

Short Questions & Answers : (2 marks for each question)

Question 1.
Write two advantages of having oxygen in air.
Answer:
Oxygen is necessary for respiration in living organisms. Oxygen reacts with food and releases energy.

Question 2.
What happens when Oxygen reacts with non-metals?
Answer:
Oxygen reacts with non-metals such as carbon. sulphur and phosphorus to form acidic oxides. C + O₂ → CO₂ \quad S + O₂ → SO₂

Question 3.
Why oxygen is called acid producer?
Answer:
The non-metals, on combustion with oxygen. produce oxides. These oxides produce acid when they react with water. So these oxides are called acidic oxides.

Question 4.
Mention some metals which absorb oxygen.
Answer:
At normal or low temperature, Au, Ag, Pt. Pb etc. can absorb oxygen. i.e can bind oxygen weakly at their surface. On heating the metal, oxygen is released.

Question 5.
What are the materials required for preparation of oxygen gas from hydrogen peroxide?
Answer:
i) delute solution of hyfrogen peroxide
ii) manganese dioxide
iii) a jute stick
iv) a test tube
v) a test tube holder

Question 6.
What are the materials required for preparation of oxygen gas from sodium peroxide?
Answer:
i) sodium peroxide
ii) distilled water
iii) conical flask
iv) a cork with two holes
v) a dropping funnel
vi) a bent delivery tube
vii) a gas jar

Question 7.
What are the materials required for preparation of oxygen gas from potasium chlorate?
Answer:
i) potassium chlorate,
ii) manganese dioxide free from carbon,
iii) a hard glass test tube,
iv) a cork with a bore,
v) a delivery tube,
vi) a stand,
vii) a gas tough,
vii) a water pot.

Question 8.
What are the materials required for laboratory preparation of hydrogen gas?
Answer:
i) impure zinc ganules
ii) dilute sulphuric acid, distilled water
iii) woulf bottle
iv) thistle funnel
v) bored cocks for wolf bottle
vi) delivery tube
vii) rubber tube
vii) grease.

Long Questions & Answers : (3 marks for each question)

Question 1.
What are the advantages of having oxygen in air?
Answer:
Oxygen is necessary for respiration in living organisms. Oxygen reacts with food and releases energy. Generation of energy from intra-cellular glucose is faster, easier and more efficient with oxygen than without it. It supports combustion. There can be no fire without oxygen.

Question 2.
What vital role oxygen play during respiration of living beings?
Answer:
The role of oxygen in the respiration of animals or plants is extremely vita!. The most important process associated with the respiration of animals is the combination of oxygen i.e combustion of simple ingradient of the carbonaceous food. As a result, the required energy is produced in the body. For example, glucose the simple ingredient of carbohydrate gets oxidised and produce energy.

Question 3.
Write down some absorber of oxygen.
Answer:
Absorber of oxygen are:
i) At normal or low temperature, Au, Ag, Pt, Pb etc. can absorb oxygen, i.e can bind oxygen weakly at their surgace. On heating the metal, oxygen is released.
ii) Alkaline potassium pyrogallate solution absorbs oxygen and turns brown.
iii) Ammoniacal cuprous chloride solution absorbs O₂ gas quickly and turns blue.

Question 4.
Write some uses of oxygen.
Answer:
i) Oxygen is used in breathing support systems by patients who cannot get enough oxygen from air due to some health problems.
ii) Oxygen is used to remove the impurities of crude iron. In this way, millions of tonnes of steel are produced.
iii) Oxygen is indepensable in manufacturing nitric acid (HNO₃) and sulphuric acid (H_{2 4}).

Question 5.
Write the way of preparation of oxygen in laboratory with the equation.
Answer:
In laboratory Oxygen can be prepared by heating together four parts of potassium chlorate and one part of manganese dioxide. Manganese dioxide acts as the catalyst. It is not consumed in the reaction. It only help potassium chlorate to decompose faster and at lower temperature. The equation of the reaction for such production of oxygen is-

2 KClO₃ + [MnO₂] → 2 KCl + 3 O₂ + [MnO₂]

Question 6.
Write some use of hydrogen.
Answer:
a) Hydrogen is used to produce ammonia, which is use in the production of urea fertiliser.
b) It is used to produce various petrochemicals.
c) For the production of hydrogenated vegetable oils, we need hydrogen.

Question 7.
Write some physical properties of oxygen.
Answer:
Some properties of oxygen are-

1. It is colourless, tasteless, odourless gas at ordinary temperature.
2. It is slightly heavier then air : Its denisty at normal temperature and pressure is 1.428 gram per litre.
3. It is slightly soluble in water: Solubility of oxygen at 0° C and 1 atm pressure is 14.8 mg per litre.
4. Freezing point of liquid oxygen is -218° C and boiling point is -183° C.
5. Oxygen has three isotopes, namely, , and though the natural abundance of the last two is very low.

Question 8.
Write two physical properties and two chemical properties of IIydrogen.
Answer:
Two physical properties of Hydrogen are-
1) Under normal conditions, hydrogen is colourless odourless. tasteless gas.
2) Hydrogen is the lightest gas. Air is about 14.4 times heavier than hydrogen.

Two chemical properties of Hydrogen are-
1) Combustibility: Hydrogen does not help in burning but it is inflammable. If a mixture of hydrogen and oxygen is burit into flame. steam is produced

2 H₂ + O₂ → 2 H₂ O

2) Reduction: Hydrogen has special attraction for oxygen. Hydrogen acts as reducing agent for its high affinity towards oxygen. Reddish-brown copper is produced by reduction of hot cupric oxide by a current of hydrogen gas. Hydrogen is oxidised to water

CuO + H₂ → Cu + H₂ O.