โจ Hydrogen โ Practice Set (Class 8, ICSE) ๐น
MCQs (12) Q1. The symbol of hydrogen is:
a) Hโ
b) H
c) Hy
d) He
๐
Answer: b) H
Q2. Atomic number of hydrogen is:
a) 0
b) 1
c) 2
d) 3
๐
Answer: b) 1
Q3. Hydrogen was discovered by:
a) Cavendish
b) Lavoisier
c) Boyle
d) Rutherford
๐
Answer: a) Cavendish
Q4. Hydrogen is collected over:
a) Mercury
b) Water
c) Oil
d) Alcohol
๐
Answer: b) Water
Q5. Which property makes hydrogen different from other gases?
a) It is heavier than air
b) It is the lightest gas
c) It is poisonous
d) It has color
๐
Answer: b) It is the lightest gas
Q6. Reaction of Zn with dilute HCl gives:
a) ZnO
b) ZnClโ + Hโ
c) Zn(OH)โ
d) Zn + Clโ
๐
Answer: b) ZnClโ + Hโ
Q7. Hydrogen is:
a) Combustible
b) Supporter of combustion
c) Both a & b
d) Neither a nor b
๐
Answer: a) Combustible
Q8. In the sun, hydrogen atoms fuse to form:
a) Oxygen
b) Helium
c) Nitrogen
d) Carbon
๐
Answer: b) Helium
Q9. The process of converting oils to ghee using hydrogen is called:
a) Hydrolysis
b) Hydrogenation
c) Oxidation
d) Sublimation
๐
Answer: b) Hydrogenation
Q10. Hydrogen is used in Haberโs process to make:
a) HCl
b) NHโ
c) HโSOโ
d) CHโ
๐
Answer: b) NHโ
Q11. Which of the following metals react with dilute acids to produce hydrogen?
a) Copper
b) Zinc
c) Silver
d) Gold
๐
Answer: b) Zinc
Q12. Hydrogen is:
a) Metallic element
b) Non-metal
c) Metalloid
d) Noble gas
๐
Answer: b) Non-metal
๐น Short Answer (8)
Q13. Why is hydrogen called the lightest element?
๐ Answer: Because it has only one proton and one electron, with atomic mass = 1.
Q14. Write one physical property of hydrogen.
๐ Answer: Hydrogen is colorless, odorless, tasteless, and the lightest gas.
Q15. Why is hydrogen not filled in modern balloons?
๐ Answer: Because it is highly inflammable and dangerous.
Q16. Name two natural sources of hydrogen.
๐ Answer: Water (HโO) and natural gas (CHโ).
Q17. Write the chemical equation for the reaction of Zn with HCl.
๐ Answer:
Zn + 2HCl \rightarrow ZnCl_2 + H_2 โ
Q18. Which metal is commonly used in the lab preparation of hydrogen and why?
๐ Answer: Granulated zinc, because it reacts steadily with dilute HCl or HโSOโ.
Q19. Write one industrial use of hydrogen.
๐ Answer: Manufacture of ammonia (Haberโs process).
Q20. What happens when hydrogen burns in oxygen?
๐ Answer: It forms water and releases a large amount of energy.
2H_2 + O_2 \rightarrow 2H_2O + \text{energy}
๐น Long Answer (6)
Q21. Explain the laboratory preparation of hydrogen with a diagram.
๐ Answer: Use Woulfโs bottle, zinc granules + dilute HCl. Gas collected over water. Equation:
Zn + 2HCl \rightarrow ZnCl_2 + H_2 โ
Q22. State three chemical properties of hydrogen.
๐ Answer:
- Burns in oxygen to form water.
- Reduces metallic oxides to metals.
- Combines with nitrogen to form ammonia.
Q23. Why is hydrogen called a clean fuel?
๐ Answer: Because its combustion produces only water, no harmful gases like COโ or SOโ.
Q24. Explain the role of hydrogen in hydrogenation of oils.
๐ Answer: Unsaturated oils are heated with hydrogen in the presence of nickel catalyst to form saturated fats (vanaspati ghee).
Q25. Compare hydrogen with oxygen (any 3 points).
๐ Answer:
- Hydrogen is lighter; oxygen is heavier than air.
- Hydrogen burns; oxygen supports burning.
- Hydrogen atomic number = 1; oxygen atomic number = 8.
Q26. Why is hydrogen not considered a good fuel for daily use, though it has high calorific value?
๐ Answer: Because it is difficult to store, highly inflammable, and requires special cylinders.
๐น Diagram / Activity Based (4
Q27. Draw a neat diagram of the laboratory preparation of hydrogen and label:
- Woulfโs bottle
- Delivery tube
- Water trough
- Gas jar
Q28. Show by a word equation and diagram how hydrogen reduces CuO to copper.
๐ Answer:
CuO + H_2 \xrightarrow{heat} Cu + H_2O
Q29. Draw the atomic structure of hydrogen.
๐ Answer: One proton in nucleus, one electron revolving.
Q30. Activity: How will you prove that hydrogen is lighter than air?
๐ Answer: Fill a soap bubble with hydrogen, it rises upward, showing hydrogen is lighter than air. (Diagram: bubble floating upward).
Q 31 .Give a Test to differentiate between jar containing pure hydrogen and other hydrogen air mixture
Ans
Flame (โpopโ) test
You need: test tubes, stoppers, delivery tube, water trough (optional), lighter/taper, safety screen & goggles.
1. Take a small sample from the jar
Displace water into an inverted test tube (or fill a test tube from the jar and stopper it). Testing a small sample is far safer than testing the whole jar.
2. Bring a lighted splint to the mouth of the (inverted) test tube and very slightly unstopper it so the gas meets air at the mouth.
3. Observe:
Pure hydrogen: burns quietly with a pale blue flame at the mouth of the tube. No bang; the flame โlicksโ at the opening because mixing with oxygen happens only at the rim. The burning splint itself is extinguished inside the gas (Hโ doesnโt support combustion).
Hydrogenโair mixture (within explosive range ~4โ75% Hโ in air): gives a sharp โpopโ/small puff or even a mini explosion as the mixture ignites throughout the tube. You may see a mist of water droplets form (product water).
(Reaction: 2 Hโ + Oโ โ 2 HโO)
Why it works (quick intuition)
Pure Hโ is combustible but not a supporter of combustion. It only burns where it can mix with oxygenโi.e., at the tube mouthโso itโs gentle.
A pre-mixed Hโ + air sample already contains oxygen in the right proportions; ignition triggers rapid combustion everywhere in the sample โ the characteristic โpopโ.
Launch your Graphy