11 - Some Gases 

In this post, you can check the solutions to the exercises of Some Gases of Oasis School Science Grade 9 by Jayananda Kapadi.

Group A

1. What is air? Write down the percentage of carbon dioxide in air.
Answer: Air is a mixture of several gases and dust particles. The percentage of carbon dioxide in air is 0.03% by volume.

2. What is the percentage of nitrogen and oxygen in air?
Answer: The percentage of nitrogen in air is approximately 78.08% by volume and that of oxygen is 20.95% by volume.

3. Write down the atomic number, atomic weight, molecular formula and molecular weight of hydrogen.
Answer: Details of hydrogen are mentioned below:
  • Atomic number - 1
  • Atomic weight - 1
  • Molecular formula - $H_2$
  • Molecular weight - 2
4. Name the scientist who discovered hydrogen gas.
Answer: Scientist Henry Cavendish discovered hydrogen gas.

5. Write any two physical properties of hydrogen gas.
Answer: Any two physical properties of hydrogen gas are:
  • It is colorless, odorless and tasteless gas.
  • It is highly inflammable gas. 
6. What is a catalyst? Write with examples.
Answer: A catalyst is a chemical substance that affects the rate of chemical reaction. Examples are: Manganese dixide, Glycerine, etc.

7. How is hydrogen gas tested? Write.
Answer: When a burning matchstick is bought into a gas jar containing hydrogen gas, it burns with pale-blue color and extinguishes with a pop sound.

8. Write down the melting point and boiling point of hydrogen.
Answer: The melting point and boiling point of hydrogen are -259 $^o$C and -253$^o$C.


9. Name the scientist who discovered oxygen gas.
Answer: The scientist 'Scheele' discovered oxygen gas.

10. What is the valency of oxygen? Why?
Answer: The valency of oxygen is two because it needs only two electrons, as it has 6 valence electrons, to fulfill its valence shell and gain a stable state by following octet rule.

11. Write down the molecular weight and atomic weight of oxygen.
Answer: The molecular weight of oxygen is 32 and atomic weight is 16.

12. How is oxygen gas tested?
Answer: For testing oxygen gas, a burning matchstick is brought near the gas jar containing oxygen gas. If the gas is oxygen then, that matchstick burns more brightly.

13. What is the percentage of oxygen gas in fresh air?
Answer: In fresh air, the percentage of oxygen gas is 20.95% by volume.

14. Write any two physical properties of oxygen gas.
Answer: Any two physical properties of oxygen gas are:
  • It is colorless, odorless and tasteless gas.
  • It is non-combustible but a supporter of combustion.
15. What is oxyhydrogen flame? Why is it used?
Answer: Oxyhydrogen flame is the mixture of hydrogen and oxygen gas at a very high temperature. [1]. It is used for cutting and welding metals, glasses, and thermoplastics. [2]

16. Write down the boiling point of oxygen.
Answer: The boiling point of oxygen -183$^o$C.

17. What is the percentage of nitrogen gas in air?
Answer: In air, the percentage of nitrogen gas is 78.08% by volume.

18 Write down the valency and atomic weight of nitrogen.
Answer: The valency of nitrogen is 3 and its atomic weight is 14.

19. Write down any two physical properties of nitrogen.
Answer: Following are the two physical properties of nitrogen:
  • It is colorless, tasteless and odorless gas.
  • It is neither combustible nor a supporter of combustion.
20. How is nitrogen gas tested? Write.
Answer: Nitrogen gas is tested using a burning magnesium ribbon. When a burning magnesium ribbon is brought in contact with a gas jar containing nitrogen, it burns forming yellow powder of magnesium nitride.

21. Write down the molecular formula of niter and salt petre.
Answer: The molecular formula of niter  and salt petre is KNO$_3$.


22. What is Haber's process?
Answer: Haber's process is the industrial process of producing Ammonia gas by reacting Nitrogen and Hydrogen gases in the ratio of 1:3 under 5000$^o$C and 200 to 600 atmospheric pressure, using Iron as a catalyst and Molybdenum as a promoter.

23. Name a catalyst and a promoter which is used in preparing Ammonia gas. 
Answer: In preparation of ammonia gas, Iron is used as a catalyst and Molybdenum is used as a promoter.

24. Write down the boiling points of nitrogen and oxygen.
Answer: The boiling points of nitrogen and oxygen are -196$^o$C and -183$^o$C, respectively.


About this book:

Oasis School Science Grade 10
Author: Jayananda Kapadi
Editor: Dr. Rameshwar Adhikari

About Oasis Publication:

Oasis Publication (P) Ltd.
Anamnagar, Kathmandu, Nepal
Phone: 0977-01-4224004