# NCERT Solutions for Class 9 Science Chapter 1 Matter in Our Surroundings

By using NCERT Solutions for Class 9 Science Chapter 1 Matter in Our Surroundings, students will be exposed to different types of questions which will help them in their exams. They can be used to check answers to questions, or to see how well they understand a concept.

Chapter 1 CBSE Class 9 Science NCERT Solutions help students understand the concepts better and also enable them to memorize the topics faster. These are important for students because they help to prepare students to do better during immense pressure.

## Chapter 1 Matter in Our Surroundings Class 9 Science NCERT Solutions

### In Text Questions

1. Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, cold drink, smell of perfume.

Solution

Chair, air, almonds, cold drink and smell of perfume.

2. Give reasons for the following observation:
The smell of hot sizzling food reaches you several metres away, but to get the smell from cold food you have to go close.

Solution

The smell of hot sizzling food reaches us several metres away because hot foods have a higher diffusion rate than cold foods because the diffusion rate of a gas increases with temperature.

3. A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?

Solution

This observation shows that the intermolecular space is high in liquid so the diver can easily pass through it.

4. What are the characteristics of the particles of matter?

Solution

The characteristics of the particles of matter are:
(i) The have vacant spaces between them.
(ii) The are always in motion.
(iii) There are attractive forces between particles of matter.

1. 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 chimney, honey, water, chalk, cotton, and iron.

Solution

Air, exhaust from chimney, cotton, water, honey, chalk, and iron.

2. (a) Tabulate the differences in the characteristics of states of matter.
(b) Comment upon the following : rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy, and density.

Solution

(a)

(b)

Rigidity: It is the property by virtue of which a substance can retain its shape when a force is applied to it. Solids possess the property of rigidity.

Compressibility: The property by virtue of which the volume of a substance can be decreased by applying force or pressure on it is known as compressibility. Gases have high compressibility because of large vacant spaces between the molecules of a gas.

Fluidity: It is the property by virtue of which the molecules of one substance can flow from one point to another. Liquids and gases possess fluidity.

Filling a gas container: A gas fills a container because there are negligible attractive forces between the molecules of a gas and the molecules move with very high velocities in all possible directions.

Shape: It is the de finite geometrical arrangement of constituent particles of a substance. Solids have de finite shapes.

Kinetic energy: It is the energy possessed by a particle due to its motion.

Density: Density of a substance is the mass per unit volume.

3. 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 air, but to do the same through a solid block of wood, we need a karate expert.

Solution

(a) The force of attraction between particles of gas is negligible. Thus, the particles of gas can move
in all directions and fills the vessel completely in which it is kept.

(b) Particles of gas move randomly in all directions with high speed. Therefore, the particles collide
with each other and also with the walls of the container with a force. Therefore, gas exerts pressure on the walls of the container.

(c) A wooden table has fixed shape and fixed volume, which are the main characteristics of solid. Thus, a wooden table should be called a solid.

(d) This is because in air, the attractive forces between the particles are negligible but in a solid like block of wood, there are large attractive forces between the constituent particles.

4. Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why?

Solution

Ice floats over water because ice has lower density than liquid water. This is because for a given mass, ice has larger volume than liquid water.

1. Convert the following temperatures to Celsius scale:
(a) 300 K
(b) 573 K

Solution

(a) 300 K = 300 – 273 = 27°C
(b) 573 K = 573-273 = 300°C

2. What is the physical state of water at:
(a) 250°C
(b) 100°C

Solution

(a) Vapour
(b) Equilibrium state between liquid and vapour

3. For any substance, why does the temperature remain constant during the change of state?

Solution

This is because the supplied heat is used to overcome the attractive forces between the particles.

4. Suggest a method to liquefy atmospheric gases.

Solution

The atmospheric gases can be liquefied by cooling the gases under high pressure.

1. Why does a desert cooler cool better on a hot dry day?

Solution

This is because on a hot dry day, the evaporation of water is faster due to higher temperature and lower humidity.

2. How does the water kept in an earthen pot (matka) become cool during summer?

Solution

This is because water can move out from the pores of earthen pot (matka) and it evaporates. Due to evaporation, water in the earthern pot cools down.

3. Why does our palm feel cold when we put some acetone or petrol or perfume on it?

Solution

This is because the particles of acetone or petrol or perfume (being low boiling liquids) gain energy from our palm and the surroundings and thus evaporate to cause cooling.

4. Why are we able to sip hot tea or milk faster from a saucer rather than a cup?

Solution

Because a saucer provides more surface area than a cup for evaporation of the liquid. It causes more cooling effect.

5. What type of clothes should we wear in summer?

Solution

We should wear light coloured cotton clothes in summer.

### Exercises

1. Convert the following temperatures to the Celsius scale.
(a) 293 K
(b) 470 K

Solution

(a) 293 K = 293 – 273 = 20°C
(b) 470 K = 470 – 273 = 197°C

2. Convert the following temperatures to the Kelvin scale.
(a) 25°C
(b) 373°C

Solution

(a) 25°C = 25 + 273 = 298 K
(b) 373°C = 373 + 273 = 646 K

3. Give reason for the following observations.
(a) Naphthalene balls disappear with time without leaving any solid.
(b) We can get the smell of perfume sitting several metres away.

Solution

(a) This is because naphthalene sublimes i.e. it directly changes into vapour without melting.
(b) This is because the molecules of perfume are moving with very high speed (diffusion) in all the directions.

4. Arrange the following substances in increasing order of forces of attraction between the particles: water, sugar, oxygen.

Solution

The increasing order of intermolecular forces of attraction is oxygen < water < sugar.

5. What is the physical state of water at:
(a) 25°C
(b) 0°C
(c) 100°C

Solution

(a) At 25°C, water is liquid.

(b) At 0°C, water is solid (Ice). (c) At 100°C, water is vapour (steam).

6. Give two reasons to justify that:
(a) water at room temperature is a liquid.
(b) an iron almirah is a solid at room temperature.

Solution

(a) At room temperature water is liquid because the attractive forces between the molecules of water are small and can move from one point to another.
(b) An iron almirah is a solid because the particles are held together by strong intermolecular attractive forces and these particles are very close to each other.

7. Why is ice at 273 K more effective in cooling than water at the same temperature?

Solution

Ice at 273 K is more effective in cooling than water at the same temperature because in ice, the molecules have lower energy as compared to the particles in the liquid water at the same temperature (273 K) and require latent heat of fusion for melting.

8. What produces more severe burns, boiling water or steam?

Solution

Steam produces severe burns as compared to boiling water. This is because in steam the molecules have higher kinetic energy than in boiling water.

9. Name A, B, C, D, E and F in the following diagram showing change of its state.

Solution

A. Fusion
B. Vaporisation
D. Solidification
E. Sublimation
C. Condensation
F. Sublimation