NCERT SOLUTION CLASS 9 SCIENCE CHAPTER 1 MATTER IN OUR SURROUNDINGS

NCERT SOLUTION SCIENCE CLASS 9 CHAPTER 1 ( MATTER IN OUR SURROUNDINGS)

PAGE -3

QUESTION No 1

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

ANSWER

SOLID STATE: Chair and almond.
LIQUID STATE: Cold drink
GASEOUS STATE : Air and smell of perfume

QUESTION NO 2:

Give reason 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:

Solids diffuses at a very slow rate. But if the temperature of a solid is increased then the particle of solids moves faster due to increased kinetic energy and thus diffusion of the solid particle increased in air. Hence .the smell of hot sizzling food reaches us even at a distance,but to get the smell from cold food you have to go close.

QUESTION NO 3

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

ANSWER:

The ability of a diver to cut through water in a swimming pool show that matters is made up of particles.

QUESTION NO 4:

What are the characteristics of the particles of matter?

ANSWER:

The characteristics of particles of matter are -
1. Matter is made up of small particles.
2. Particles of matter have space between them.
3. Particles of matter are continuously moving.
4. Particles of matter attract each other.

PAGE NO 6

QUESTION NO 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 chimneys,honey,water,chalk,cotton and iron.

ANSWER;

In the given substances,the increasing order of their density as follows
1. Air.
2. Exhaust from chimney.
3. Cotton
4. Water
5.Honey
6. Chalk
7. Iron

QUESTION NO 2 (a)

Tabulate the differences in the characteristics of states of matter.

(b) Comment upon the following: rigidity,compressibility,fluidity,shape,kinetic energy and density.

ANSWER;

The differences in the characteristics of the matter are given in the following table-

Solid State Liquid State Gaseous State

1. Solid has definite 1.No definite 1.Gases have neither

shape and volume shape a definite shape nor

a definite volume.

2. Incompressible 2.Compressible 2.Highly compressible
3.There is a little 3.Liquid particles 3.The space between

space between the have a greater gas particles is the

particles of solid space compare to greatest

solid

4.The force of 4.The force of 4.The force of

attraction among attraction among attraction is least

the solid particles liquid particles are between the gaseous
are higher less than solid particles
5.Particles of solid 5.Particles of liquid 5.Gaseous particles
cannot move move freely are in a continuous
freely random motion

Answer 2 (b)

Rigidity------- It can be expressed as the tendency of matter to resist a change in shape.

Compressibility------ It is the ability to reduce to a lower volume when force is applied.

Fluidity ------ It is the ability to flow.

By Filling a gas container---------

Shape------ It defines a definite boundary.

Kinetic Energy-------- It is the energy of a particle due to its motion.

Density---------- It is the mass per unit volume.

QUESTION NO 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.

ANSWER:

(a) There is less attraction between particles of gas. Thus gas particles move freely in all directions. Hence gas completely fills the vessel in which it is kept.

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

(c) A wooden table has a definite shape and volume. It is rigid and cannot be compressed so it has the characteristics of a solid. So it is called solid.

(d) Particles of air have large spaces between them. That's why we can easily move our hand in air. while wood has little space between the particles. It is rigid also. Because of this reason we need a karate expert to move our hand, because more force is required.

QUESTION NO 4

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

ANSWER :

In the solid state, when water molecules come close to each other, the molecules are forced to align in a very particular structure a hexagonal lattice. It is tiny pores in which air is present. Due to increased bond angles and expanded molecular structure this implies greater volume and hence it has lower density.

Density = Mass/Volume

This is the reason why ice floats on water.

PAGE 9

QUESTION NO 1

Convert the following temperature to celsius scale ;

(a) 300 K (b) 573 K

ANSWER:

(A) 300K = (300-273) = 27 Degree centigrade.

(B) 573 K = (573-273) = 300 Degree centigrade.

QUESTION NO 2

What is the physical state of water at ;

(A) 250 Degree centigrade (B) 100 Degree Centigrade

ANSWER NO 2

(A) Water at 250 degree centigrade exists in gaseous state.

(B) At 100 degree centigrade water can exists in both liquid and gaseous form. At this temperature, after getting the heat equal to the latent heat of vaporization, water starts changing from liquid state to gaseous state.

QUESTION NO 3

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

ANSWER NO 3

During the change of state, the temperature remains constant. This is due to all the heat supplied to increase the to increase the temperature is utilised (as latent heat) in changing the state by overcoming the force of attraction between the particles. Therefore, this heat does not contribute in increasing the temperature of the substance.

QUESTION NO 4

Suggest a method to liquefy atmospheric gases.

ANSWER

Atmospheric gases can be liquefied by applying pressure and reducing temperature.

PAGE NO 10

QUESTION NO 1

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

ANSWER NO 1

PRINCIPLE:

When a liquid evaporates, the particle of the liquid absorb energy from the surroundings to compensate the loss of energy during evaporation. This makes the surroundings cool.

In desert cooler, the water from inside the cooler evaporate. This lead to absorption of energy from the surroundings, hence it cools the surroundings. In hot dry day the amount of water vapour present in air less, thus water present inside the cooler evaporates more, hence cools the surroundings.

QUESTION NO 2

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

ANSWER NO 2

There are some pores in an earthen pot through which the liquid inside the pot evaporates, hence the evaporated particle of the liquid absorb energy from the pot to compensate the loss of energy during evaporation. This evaporation makes the water inside the pot cool.

QUESTION NO 3

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

ANSWER NO 3

When we put some acetone or perfume or petrol on our palm, it evaporates. During evaporation, particles of liquid absorb energy from the surrounding and the surface of the palm to compensate the loss of energy, making the palm cool.

QUESTION NO4

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

ANSWER NO 4

In a saucer the surface area of tea is greater than the cup.

Hence it evaporates faster in a saucer and cools the hot tea faster in compare to cup. Because of this reason we are able to sip hot tea or milk faster from a saucer than a cup.

QUESTION NO 5

What type of clothes should we wear in summer?

ANSWER NO 5

We should wear cotton clothes in summer. We sweat more in summer and cotton clothes are good absorber of water. It absorb sweat from the body and expose the liquid to the atmosphere and evaporation takes place. During evaporation, particles on the surface of the liquid gain energy from our body surface, making the body cool.

EXERCISE PAGE NO 12

QUESTION NO 1

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

ANSWER

(a) 293 K = 293-273 = 20 degree centigrade
(b) 470 K = 470-273 = 197 degree centigrade

QUESTION NO 2

Convert the following temperatures to the kelvin scale.
(a) 25 degree centigrade
(b) 373 degree centigrade

ANSWER

(a) 25 degree centigrade = 25 + 273= 298 K
(b) 373 degree centigrade = 373+273 = 646 K

QUESTION NO 3

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

ANSWER

(a) Naphthalene balls has the property of sublimation. Evaporation of naphthalene balls takes place easily and it disappear with time without leaving any solid.

(b) Gaseous particle have less intermolecular force hence they move rapidly. So perfume diffuse in air easily. That's why we can smell perfume sitting several meters away.

QUESTION NO 4

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

ANSWER

Oxygen,water,sugar

QUESTION NO 5

What is physical state of water at---
(a) 25 degree centigrade (b) 0 degree centigrade (c) 100 degree centigrade

ANSWER

(a) Liquid
(b) Solid and Liquid
(c) Liquid and Vapour

QUESTION NO 6

Give two reason to justify--------

(a) Water at room temperature is a liquid.
(b) An iron almirah is a solid at room temperature.

ANSWER --

(a) Water at room temperature is a liquid because it has fluidity and
(i) has definite volume
(ii) but no definite shape

(b) An iron almirah is a solid at room temperature because
(i) it is rigid
(ii) and has a definite shape

QUESTION NO 7

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

ANSWER---

Ice at 273 K is less energetic than water at same temperature. Because at this temperature water contains latent heat of fusion. So it has less cooling effect.