Questions and Answers Chapter 1 “Matter in Our Surroundings” NCERT Science Class 9
Questions and Answers:
In-text Questions:
Page 3:
- Which of the following are matter?
(a) Chair, (b) Air, (c) Love, (d) Smell, (e) Hate, (f) Almonds, (g) Thought, (h) Cold, (i) Smell of perfume.
Answer: Chair, Air, Almonds, Smell of perfume.
Page 6:
- Give reasons for the following observation: The smell of hot sizzling food reaches you several meters away, but to get the smell from cold food you have to go close.
Answer: The smell of hot sizzling food reaches us several meters away due to the higher kinetic energy of the gas molecules at higher temperatures. These molecules diffuse faster and spread out over a larger area. Cold food has less kinetic energy and thus the gas molecules do not diffuse as fast, requiring us to be closer to detect the smell.
- A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?
Answer: This observation shows that matter (water) is made up of particles that have space between them, allowing the diver to cut through it.
Page 9:
- What are the characteristics of the particles of matter?
Answer: The characteristics of the particles of matter are:
– Particles of matter have space between them.
– Particles of matter are continuously moving.
– Particles of matter attract each other.
Page 10:
- The mass per unit volume of a substance is called density (density = mass/volume). Arrange the following in order of increasing density – air, exhaust from chimneys, honey, water, chalk, cotton, and iron.
Answer: Air < Exhaust from chimneys < Cotton < Water < Honey < Chalk < Iron.
Page 11:
- (a) Tabulate the differences in the characteristics of states of matter.
Answer:
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Definite shape | No definite shape | No definite shape |
| Volume | Definite volume | Definite volume | No definite volume |
| Compressibility | Negligible | Very little | High |
| Fluidity | Cannot flow | Can flow | Can flow |
| Density | High | Medium | Low |
| Kinetic Energy | Low | Moderate | High |
(b) Comment upon the following: rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy, and density.
Answer:
– Rigidity: Solids exhibit rigidity, meaning they retain their shape.
– Compressibility: Gases are highly compressible; liquids and solids are not.
– Fluidity: Liquids and gases can flow; solids cannot.
– Filling a gas container: Gases fill the container completely and uniformly.
– Shape: Solids have a fixed shape; liquids take the shape of their container; gases do not have a fixed shape.
– Kinetic Energy: Particles in solids have the least kinetic energy, liquids have more, and gases have the most.
– Density: Solids have high density, liquids have moderate density, and gases have low density.
Page 14:
- Give reasons:
(a) A gas fills completely the vessel in which it is kept.
(b) A gas exerts pressure on the walls of the container.
(c) A wooden table should be called a solid.
(d) We can easily move our hand in the air but to do the same through a solid block of wood we need a karate expert.
Answer:
(a) Gas molecules move randomly and spread out to fill the entire volume of the container.
(b) Gas molecules are in constant motion and collide with the walls of the container, exerting pressure.
(c) A wooden table has a definite shape and volume, indicating rigidity and hence it is a solid.
(d) Air has less intermolecular force, allowing easy movement; a solid block has strong intermolecular forces, requiring more force to move through it.
Page 15:
- Liquids generally have a lower density as compared to solids. But you must have observed that ice floats on water. Find out why.
Answer: Ice floats on water because it is less dense than water. The structure of ice has more open spaces due to hydrogen bonding, making it less dense.
Exercises:
Page 18:
- Convert the following temperatures to the Celsius scale:
(a) 300 K (b) 573 K
Answer:
(a) 300 K = 27°C
(b) 573 K = 300°C
- What is the physical state of water at:
(a) 250°C (b) 100°C
Answer:
(a) 250°C – Gaseous state (steam)
(b) 100°C – Both liquid and gaseous states (boiling point of water)
- For any substance, why does the temperature remain constant during the change of state?
Answer: The temperature remains constant during the change of state because the heat energy supplied is used to overcome the intermolecular forces of attraction rather than increasing the kinetic energy of the particles.
- Suggest a method to liquefy atmospheric gases.
Answer: Atmospheric gases can be liquefied by increasing pressure and decreasing temperature, which brings the gas molecules closer together and forces them into a liquid state.
- Why does a desert cooler cool better on a hot dry day?
Answer: A desert cooler cools better on a hot dry day because the evaporation of water is faster, which absorbs more heat from the surroundings, leading to better cooling.
- How does the water kept in an earthen pot (matka) become cool during summer?
Answer: Water kept in an earthen pot cools due to the process of evaporation. The tiny pores in the pot allow water to seep out and evaporate, which absorbs heat from the water inside the pot, making it cool.
- Why does our palm feel cold when we put some acetone or petrol or perfume on it?
Answer: Our palm feels cold because acetone, petrol, or perfume evaporate quickly, absorbing heat from our skin, which makes the palm feel cold.
- Why are we able to sip hot tea or milk faster from a saucer rather than a cup?
Answer: We can sip hot tea or milk faster from a saucer because the larger surface area allows the liquid to cool down faster due to faster evaporation.
- What type of clothes should we wear in summer?
Answer: In summer, we should wear light-colored and loose cotton clothes. Light colors reflect heat, and cotton absorbs sweat and allows it to evaporate, keeping us cool.
These answers cover the major points discussed in Chapter 1 “Matter in Our Surroundings” of the NCERT Science textbook for Class 9.