April 18, 2021

Scientific Knowledge

“Learning is never done without errors.”

Imp. Ques. : Matter in Our Surroundings

Class 9 : Science : Chemistry

Imp. Ques. : Matter in Our Surroundings

Multiple Choice Questions: Choose the correct option:

  1. Evaporation of a liquid occurs at.
    (a) Boiling point
    (b) A fixed temperature
    (c) Temperature lower than boiling point
    (d) All temperatures
  2. The conversion of gas into liquid is called.
    (a) Freezing (b) Condensation
    (c) Sublimation (d) Fusion
  3. The fusion is the process in which.
    (a) Liquid changes into solid (b) Solid changes into liquid
    (c) Solid changes into gas (d) Gas changes into solid
  4. The ice floats on water because.
    (a) Its density is more than water                    (b) Its density is less than water
    (c) It has less intermolecular space                 (d) none of the above
  5. Ice at 0°C is more effective in cooling than water at the same temperature because.
    (a) It holds latent heat
    (b) The molecules use the heat to overcome the force of attraction
    (c) Both (a) and (b)
    (d) None of the above
  6. The density of water is maximum at.
    (a) 0°C (b) 100°C
    (c) 4°C (d) 273 K
  7. Solids and gases mix/dissolve in water.
    (a) Because water is a good solvent
    (b) Because water has intermolecular space
    (c) Diffusion is faster in water
    (d) All of the above
  8. Choose the correct statement from the following:
    (a) The volume of gas expands on heating.
    (b) Two gases cannot diffuse into each other.
    (c) Gas is converted into solid, it is called condensation.
    (d) Gases cannot diffuse in solids.
  9. As the pressure of air decreases, the boiling point of the liquid.
    (a) Decreases (b) increases
    (c) Does not changes (d) None of these
  10. Which among the following can exist in vapour state?
    (a) Oxygen (b) Hydrogen
    (c) Carbon dioxide (d) Water
  11. At normal pressure (1 atmospheric pressure) the boiling point of water is.
    (a) 98°C (b) 100°C
    (c) 110°C (d) 90°C
  12. The pressure of air is measured in atmosphere and pascal. 1 atmospheric pressure is equal to.
    (a) 1.0 1 32 5 x 105 Pa         (b) 1.01325 x 104 Pa
    (c) 10.1325 x 105 Pa            (d) 10.1325 x 106 Pa
  13. Cooking of rice at higher altitudes is difficult because.
    (a) Water boils at 100°C                            (b) Water boils at <100°C
    (c) Boiling point of water is constant      (d) None of the above

Answer: 1—(c), 2—(b), 3—(b), 4—(b), 5—(a), 6—(c), 7—(d), 8—(a), 9—(a), 10—(d), 11-(b), 12—(a), 13-(b).

  1. Very Short Answer Type Questions:

Question 1. Define matter.
Answer: Anything that occupies space and has mass is called matter.

Question 2. State different states of matter with an example.
Answer: Matter has 3 different states

Solid     →      Liquid   →     Gas

   Ice                     Water                Steam
Question 3. What is diffusion?
Answer. The intermingling of molecules of one substance with that of the other is called diffusion.

Question 4. What happen to the rate of diffusion if the temperature is increased?
Answer: With increased temperature, the rate of diffusion also increases as the particles gain energy and vibrate more.

Question 5. Name the state of matter that have the tendency to maintain their shape when subjected to outside force.
Answer: Solid.

Question 6. Define melting point.
Answer: The temperature at which a solid melt to become liquid at the atmospheric pressure is called its melting point.

Question 7. Define boiling point.
Answer: The temperature at which a liquid starts boiling at the atmospheric pressure is known as its boiling point.

Question 8. Define latent heat of vaporization.
Answer: Latent heat of vaporization is the heat energy required to change 1 kg of a liquid to gas at atmospheric pressure at its boiling point.

Question 9. Define latent heat of fusion.
Answer: Latent heat of fusion is the amount of heat energy required to change 1 kg of solid into liquid at its melting point.

Question 10. Define sublimation.
Answer: Sublimation is the change of gaseous state directly to solid state without going through liquid state and vice-versa.

Question 11. What is dry ice?
Answer: Solid carbon dioxide obtained by cooling and applying pressure on carbon dioxide gas. It does not melt so it is called dry ice.

Question 12. What is humidity?
Answer: The air holds water vapour, this air with water is called humid air and the phenomenon is called humidity.

Question.13. Give two properties of solid.
Answer. (1) Solids have fixed shape and are rigid. (2) Solids cannot be compressed.

Question.14. What will happen if the pressure is reduced on solid carbon dioxide (dry ice)?
Answer. If the pressure is reduced on solid carbon dioxide it will directly change into gaseous state without melting.

Question 15. dame any three substances that show sublimation.
Answer: Ammonium chloride, camphor and naphthalene balls.

Question 16. Sponge is solid, but we can still compress it. Why?
Answer: Sponge is a solid with minute pores in it. When we press the sponge the air present in these pores is released out and hence we are able to compress it.

Question 17. What is normal atmospheric pressure?
Answer: The atmospheric pressure at sea level is 1 atmosphere and taken as the normal atmospheric pressure.

Question 18. What is Kelvin?
Answer: Kelvin is the SI unit of temperature (0°C = 273 K).

Question 19. Give two examples of diffusion.
Answer: Milk drops dissolved in water and perfume sprayed in a room.

Question 20. Give the temperature at which water exists in two different phases/states.
Answer: At 0°C water can be in solid or in liquid state.
At 100°C water can be in liquid or in gaseous state.

 

  1. Short Answer Type Questions


Question 1. Why do we see water droplets collected on the outer surface of a glass container, containing ice?
Answer: The water vapour present in air, comes in contact with the cold outer surface of the container thereby condensing it to form water droplets.

Question 2. Explain why solids have fixed shape but liquids and gases do not have fixed shape.
Answer: Solids have fixed shape due to strong intermolecular force of attraction between them. The liquids and gases have molecules with less intermolecular force of attraction and hence they can flow and take shape of the container.

Question 3. Liquids and gases can be compressed but it is difficult to compress solids. Why?
Answer: Liquids and gases have intermolecular space, on applying pressure externally on them the molecules can come closer thereby minimizing the space between them. But in case of solids there is no intermolecular space to do so.

Question 4. A balloon when kept in sun, bursts after some time. Why?
Answer: The balloon has air filled in it. The balloon when kept in sun gets heated and the air inside it also gets heated. The molecules of air get energy, and vibrate faster thereby exerting large force on the walls of the balloon. Due to this expansion of gases the balloon bursts.

Question 5. Why do people perspire a lot on a hot humid day?
Answer: On a hot, humid day, due to the heat our body starts sweating for the cooling mechanism i.e., by evaporation and gets cooling effect. But the air cannot hold any more water on a humid day and therefore the sweat or perspiration is seen.

Question 6. Distinguish between evaporation and boiling.
Answer:

S.N. Evaporation Boiling
1. Evaporation is a surface phenomenon. Boiling is a bulk phenomenon.
2. It is a slow process. It is a fast process.
3. It takes place at all temperatures. It takes place at a definite temperature.

Question 7. Why is it advisable to use pressure cooker at higher altitudes?
Answer: At higher altitudes, the atmospheric pressure is low and the water boils very fast and evaporates at faster rate therefore the pressure is required to increase the cooking process and this is done by using pressure cooker which increases the pressure inside the container and cooks food faster.

Question 8. What are fluids?
Answer: The states of matter that can flow due to less intermolecular force of attraction, are liquids and gases and are called as fluids.

Question 9. One kg cotton and one kg sand, which is more denser? Why?
Answer: One kg sand is more denser than 1 kg cotton because density = mass/volume .
The volume required by cotton is more than the sand and density and volume are inversely proportional.

Question 10. Why is water liquid at room temperature?
Answer: At room temperature, the molecules of water have some intermolecular force of attraction and the room temperature cannot provide sufficient heat for these molecules to overcome their force of attraction and therefore remain in liquid phase.

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