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NCERT Solution Science Class 9 Matter in our Surroundings




In this page we have NCERT solutions for Class 9 Matter in our Surroundings . Hope you like them and do not forget to like , social shar and comment at the end of the page.

Question 1

Which of the following are matter?

Chair, air, love, smell, hate, almonds, thought, cold, cold drink, smell of perfume.


Answer

The matter are Chair, air, almonds and cold drink

Question 2

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

Solids diffuse at a very slow rate. But, if the temperature of the solid is increased, then the rate of diffusion of the solid particles into air increases. This is due to an increase in the kinetic energy of solid particles. Hence, the smell of hot sizzling food reaches us even at a distance, but to get the smell from cold food we have to go close.

Question 3

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 the matter is made of particles and particles of matter have intermolecular spaces.
Question 4

What are the characteristics of particles of matter?

Answer

The characteristics of particles of matter are:

a) Particles of matter have spaces between them.
b) Particles of matter are continuously moving.
c) Particles of matter attract each other.

Question 5

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.

Answer
We know from definition of density, gas would have least density, liquid would in between and solid will have highest density. So keeping these in mind, order of increasing density will be


air < Exhaust from chimneys < cotton < water < honey < chalk < iron.


Question 6

(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.

Answer

(a)

Property

Solid state

Liquid state

Gaseous state

1

Definite shape and volume.

No definite shape. Liquids attain the shape of the vessel in which they are kept.

Gases have neither a definite shape nor a definite volume.

2.

Incompressible

Slightly Compressible

Highly compressible

3.

Cannot flow

Can flow

Can flow

4.

Particles don't move freely

Particles move freely but are confined within boundary.

Particles move freely.

5.

Force of attraction between particles are maximum.

Force of attraction between particles is less than solid but more than that in gas

Force of attraction between particles is least.


(b)

Rigidity

It is the tendency of matter to resist the change of its shape

Compressibility

It is the property of matter in which its volume is decreased by applying force.

Fluidity

It is the ability of matter to flow.

Filling a gas container

On filling a gas takes the shape of the container

Shape

Having definite boundaries

Kinetic Energy

It is the energy possessed by the particles of matter due to its motion.

Density

It is mass per unit volume



Question 7

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)

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

b)

Particles of gas move randomly in all directions at high speed. As a result, the particles hit each other and also hit 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)

Particles of air have large spaces between them. On the other hand, wood has little space between its particles. Also, it is rigid. For this reason, we can easily move our hands in air, but to do the same through a solid block of wood, we need a karate expert.



Question 8

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

Answer

Ice which is a solid has vacant spaces between water molecules thus making ice lighter than water. Thus ice floats on water.

Question 9

 Convert the following temperature to Celsius scale:

(a) 300 K


(b) 573 K


Answer

a) 300 K = (300 - 273)°C
= 27°C


b) 573 K = (573 - 273)°C
= 300°C


Question 10

What is the physical state of water at:

(a) 250°C

(b) 100°C


Answer

2500C

Gaseous State (As Boiling temperature of water is 100° C).

100°C

Since water boils at this temperature thus it can exist 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 11

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

Answer

During the change of state of any substance, the heat supplied or released is utilized in phase change. Such heat is called latent heat. So, the temperature of any substance remains constant during the change of state.


Question 12

Suggest a method to liquefy atmospheric gases.

Answer

The gases can be converted into liquids by decreasing temperature or by increasing pressure.

Question 13

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

Answer

A desert cooler increases the humidity of the surrounding air. The water particles in the air take the heat from the surrounding objects and evaporates. In hot and dry days the moisture level is very low in atmosphere which increases the rate of evaporation. Because of faster evaporation, cooler works well. That’s why desert cooler cool better on a hot dry day.

Question 14

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

Answer

There are some pores in an earthen pot through which the liquid inside the pot evaporates. This evaporation makes the water inside the pot cool. In this way, water kept in an earthen pot becomes cool during summers.

Question 15

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

Answer

Acetone, petrol, and perfume evaporate at low temperatures. When some acetone, petrol, or perfume is dropped on the palm, it takes heat from the palm and evaporates, thereby making the palm cooler.

Question 16

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

Answer

A liquid has a larger surface area in a saucer than in a cup. Thus, it evaporates faster and cools faster in a saucer than in a cup. Thus, we are able to sip hot tea or milk faster from a saucer than a cup.

Question 17

What type of clothes should we wear in summers?

Answer

We should wear cotton clothes in summers as cotton is a good sweat absorber. Sweat is absorbed by the cotton and is exposed to the atmosphere making evaporation faster. During this evaporation, particles on the surface of the liquid gain energy from our body surface, making the body cool.


Question 18

Convert the following temperatures to Celsius scale.

(a) 300 K

(b) 573 K

Answer

a) 300 K = (300 - 273) °C
= 27 °C

b) 573 K = (573 - 273) °C
= 300 °C

Question 19

Convert the following temperatures to Kelvin scale.

(a) 25°C

(b) 373°C
Answer

a) 25 °C = (25 + 273) K
= 298 K

b) 373 °C = (373 + 273) K
= 646 K



Question 20

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 meters away.

Answer

(a) Naphthalene balls disappear with time without leaving any solid because they undergo sublimation easily i.e., the change of state of naphthalene from solid to gas takes place easily.

(b) Perfumes has high degree of vaporization and its vapour diffuse into air easily. Therefore, we can get the smell of perfume sitting several metre away.

Question 21

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

Answer

Oxygen -> Water -> Sugar.

Question 22

What is the physical state of water at-

(a) 25°C
(b) 0°C

(c) 100°C

Answer

250C

Liquid State

0°C

Solid State or liquid state .

100°C

Gaseous State, can also be in liquid state



Question 23 Give two reasons 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 also it has no shape but has a fixed volume that is, it occupies the shape of the container in which it is kept.

(b) An iron almirah is a solid at room temperature it has rigid and fixed shape.

Question 24

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

Answer

Ice at 273 K has less energy than water (although both are at the same temperature). Water possesses the additional latent heat of fusion. Hence, at 273 K, ice is more effective in cooling than water.

Question 25

What produces more severe burns, boiling water or steam?

Answer

Steam has more energy than boiling water. It possesses the additional latent heat of vaporization. Therefore, burns produced by steam are more severe than those produced by boiling water.

Question 26

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



Answer

A -> Fusion

B-> Vaporization

C->Condensation

D-> Solidification

E->Sublimation

F-> Sublimation


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