Matter in Our Surroundings"

 

Here are 10 Higher Order Thinking Skill (HOTS) questions from the Class 9 Science chapter "Matter in Our Surroundings":

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Higher Order Thinking Skill (HOTS) Questions – Chapter: Matter in Our Surroundings

1. Why do camphor and dry ice disappear without leaving any residue? What does this tell you about their physical properties?

2. If water boils at 100°C at sea level, why does it boil at a lower temperature on a mountain? Explain in terms of atmospheric pressure.

3. Why is it more comfortable to wear cotton clothes in summer than synthetic clothes? Relate your answer to the concept of evaporation.

4. Two substances are kept in an open container: one disappears gradually while the other remains. What can you infer about their physical state and volatility?

5. Why do we see water droplets on the outer surface of a cold bottle taken out from the refrigerator? Explain the process involved.

6. How would you prove that air is matter even though it is invisible? Suggest a simple experiment.

7. What would happen if you try to compress a gas in a sealed syringe? What property of matter does this demonstrate?

8. Can solids diffuse into liquids? If yes, give a practical example and explain the mechanism involved.

9. Why does sweating help to cool our body? How does this relate to the concept of latent heat?

10. Suppose a gas is compressed at constant temperature. What changes would you observe in its density and why?

Here are the answers to the 10 Higher Order Thinking Skill (HOTS) questions from the Class 9 Science chapter "Matter in Our Surroundings":

Answers: HOTS – Matter in Our Surroundings

1. Why do camphor and dry ice disappear without leaving any residue?

Answer: Camphor and dry ice undergo sublimation, changing directly from solid to gas without becoming liquid. This indicates they have weak intermolecular forces and high vapor pressure at room temperature.

2. If water boils at 100°C at sea level, why does it boil at a lower temperature on a mountain?

Answer: Atmospheric pressure is lower at higher altitudes. Since boiling occurs when vapor pressure equals atmospheric pressure, water boils at a lower temperature on mountains.

3. Why is it more comfortable to wear cotton clothes in summer than synthetic clothes?

Answer: Cotton absorbs sweat and allows it to evaporate faster due to more surface area and breathability. Evaporation causes cooling, making us feel comfortable.

4. Two substances are kept in an open container: one disappears gradually while the other remains. What can you infer?

Answer: The one that disappears is likely a volatile substance (like a liquid or sublimable solid), showing higher vapor pressure. The other is less volatile or non-volatile.

5. Why do we see water droplets on the outer surface of a cold bottle?

Answer: Water vapor from air condenses on the cold bottle surface due to temperature drop below dew point. This process is condensation.

6. How would you prove that air is matter even though it is invisible?

Answer: Air occupies space and has mass. A simple proof: Weigh a deflated balloon and then an inflated one—the inflated one is heavier, showing air has mass.

7. What would happen if you compress a gas in a sealed syringe?

Answer: The gas volume decreases, pressure increases, but mass remains same. This demonstrates that gases are compressible and their particles are far apart.

8. Can solids diffuse into liquids? Give an example.

Answer: Yes. Example: Sugar or salt dissolving in water. The particles of solid diffuse into the liquid due to kinetic energy and intermolecular space.

9. Why does sweating help to cool our body?

Answer: Sweat evaporates from the skin, absorbing latent heat of vaporization from the body, thereby reducing body temperature and causing cooling.

10. What happens if a gas is compressed at constant temperature?

Answer: Its volume decreases, density increases, and pressure increases. Since mass remains the same and volume decreases, density rises. (Density = Mass/Volume)