# NCERT Solutions for Class 9 Science Chapter 1

NCERT Solutions for Class 9 Science Chapter 1 – Matter in our Surroundings, contains solutions to various questions in Exercises for Chapter 1. Matter in our Surrounding Class 9 NCERT Solutions have been explained in a simple and easy to understand manner. We are providing all subjects which can be accessed by clicking here.

## Download NCERT Solutions for Class 9 Science Chapter 1 – Matter in our Surroundings

### NCERT Solutions for Class 9 Science Chapter 1 – Matter in our Surroundings – NCERT Exercises

NCERT Solutions for Class 9 Science Chapter 1 – Matter in our Surroundings, Exercises includes all in text and exercise solved questions which helps you to understand the topic covered in Chapter 1 Matter in our Surroundings Class 9, in a better manner to help you to score good marks in your examinations.

### NCERT Solutions for Class 9 Science Chapter 1 – Intext Questions: Page 3

1. Which of the following are matter?

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

Anything which occupies space and has mass is called matter. So the following items are matter: Chair, air, almonds, cold-drink and smell of perfume.

2. Give reason for the following observation.

The smell of sizzling food reaches several meters away, while to get the smell from cold food you have to go close.

The particles of matter possess kinetic energy and are moving continuously. As the temperature increases, kinetic energy increases. Particles of hot vapors coming out of hot sizzling food move faster and reach us several meters away while vapors coming out from cold food move slowly and cannot reach us.

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

The forces of attraction between the water molecules are not very strong as compared to solids. By applying some force, the diver is able to cut through water. This observation shows that water molecules have smaller force of attraction between them.

4. What are the characteristics of particles of matter?

Characteristics of particles of matter are,

1. Matter is made up of very tiny particles not visible by naked eye.
2. Particles of matter have space between them
3. The particles of matter are continuously moving as they have kinetic energy.
4. The constituent particles of matter are held together by forces of attraction.

### NCERT Solutions for Class 9 Science Chapter 1 – Intext Questions: Page 6

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.

Air < exhaust from chimney < cotton < water < honey <  chalk < iron.

2. a) Tabulate the differences in the characteristics of matter.

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

a)

b) Rigidity-Rigidity refers to the tendency to maintain shape when an outside force is applied.

Compressibility- Compressibility means the tendency to decrease volume upon the application of some outside force.

Fluidity- Fluidity is the tendency to flow. Gases have the maximum fluidity.

Density- Density is mass per unit volume. Solids have the highest density.

3. Give reasons:

a) A gas fills the vessel completely 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.

a) The particles of a gas have the least forces of attraction and can randomly move in all directions. Hence, they do not have a fixed volume and completely occupy the vessel in which it is kept.

b) The particles of gas possess high kinetic energy and constantly move within the container. As a result of the movement, particles hit each other as well as the walls of the container. The force with which the particles strike the walls of the container exerts pressure on the walls.

c) A wooden table has a definite shape and a fixed volume. It is very rigid and incompressible, therefore should be called a solid.

d) The particles of gas have negligible forces of attraction which can easily be overcome for the movement of the hand. In contrast, the forces of attraction between the particles of solid is very strong and these particles have least space between them. Thus, there is no possibility of moving our hand through a block of wood.

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

Ice has a cage-like structure i.e. when water solidifies, a number of empty spaces are created because of trapping of air bubbles. So, the volume increases for the same mass of water i.e. mass per unit volume or density is lower than that of water. Therefore, ice floats on water.

### Intext Questions: Page 9

1. Convert the following temperatures to Celsius scale.

i. 300K
ii. 573K

Formula for the conversion of Kelvin to Celsius scale is :

[K-273=°C]

i. 300K – 273= 27°C

ii. 573K – 273= 300°C

2. What is the physical state of water at

i. 250°C
ii. 100°C

Ans.

The physical state of water at

i. 250°C is water vapor
ii. 100°C , liquid water and water vapor exist in equilibrium.

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

During the change of state of a substance, the temperature remains constant because the heat supplied to the substance is used up in overcoming the forces of attraction between them and thus the thermometer does not show any rise in temperature. This heat is also called latent heat because it remains hidden.

4. Suggest a method to liquefy atmospheric gases.

Atmospheric gases can be liquefied by cooling the gas under high pressure. Because of these conditions, the distance between the particles will decrease and their kinetic energy decreases.

### NCERT Solutions for Class 9 Science Chapter 1 – Intext Questions : Page 10

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

On a hot dry day, the temperature is high and humidity is low. Both these factors cause an increase in the rate of evaporation . A desert cooler works on the principle of evaporation. The water takes heat from the hot desert cooler and evaporates making the environment around it cool.

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

Due to the small pores present in the walls of the earthen pot, water comes out slowly. As it comes out on the surface of matka, it evaporates. The heat energy required for the evaporation is taken from the water kept in it. This results in lowering of the heat content of the water and the water becomes cool.

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

Acetone and petrol have low boiling points. When these are put on palm, they evaporate very quickly. The energy required for evaporation is is gained from the palm, thus causes cooling effect.

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

When hot tea or milk is placed in a saucer, the surface area of liquid increases in comparison to cup. Thus evaporation of hot liquid occurs faster and more cooling is observed in a saucer.

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

We should wear light coloured cotton clothes in summer because cotton is a good absorbent of water. It absorbs sweat quickly and exposes it to atmosphere for easy evaporation, thereby helps us in keeping our body cool.

### NCERT Solutions for Class 9 Science Chapter 1 – NCERT Exercise: Page 12

1. Convert the following temperatures to Celsius scale.

a) 293K
b) 470K

We know that, °C = K – 273

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

2. Convert the following temperatures to Kelvin scale.

a) 25°C
b) 373°C

We know that,  K = °C + 273

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

3. Give reasons 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.

a) Naphthalene balls are sublimable in nature, thus it can directly convert from solid to gas by taking heat from surroundings, through the process known as sublimation.

b) The smell of perfume reaches several meters away due to diffusion. The particles of perfume mix well with the air particles and due to the high speed of these particles, we can get the smell of perfume sitting several meters away.

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

The forces of attraction between the particles are maximum in solids, followed by liquids and the weakest in gaseous state.

Oxygen(solid) <  Water(liquid) < Sugar (solid)

5. What is the physical state of water at –

a) 25°C
b) 0°C
c) 100°C

The physical state of water at –

a) 25°C is liquid
b) At 0°C, both solid and liquid are in equilibrium
c) At 100°C, both liquid and gaseous state (steam) are in equilibrium.

6. Give two reasons to justify –

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

a) Water at room temperature is a liquid because,

i. Liquids do not have a fixed shape:

Water takes the shape of the container in which it is kept, so it is a liquid.

ii. Liquids have a fixed volume:

If we take 50ml water in a beaker and then transfer it to a glass, the volume of water will remain fixed.

b) An iron almirah is solid at room temperature because,

i. Solids have a fixed shape as well as fixed volume:

Since iron almirah has a fixed shape as well as fixed volume, it is a solid.

ii. Solids are incompressible:

If we apply some force, volume of iron almirah will not decrease. Thus it is a solid because it’s incompressible.

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

When ice melts to form water, it absorbs energy equal to the latent heat of fusion from surroundings. Thus, ice at 273K has lesser heat energy than water at 273K and therefore it is more effective in cooling than water at the same temperature.

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

Steam causes more severe burns than boiling water because when water is converted to steam, it absorbs energy equal to latent heat of vaporization . Thus, steam has more heat energy and produces more severe burns than boiling water.

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

A. Melting/Fusion
B. Vaporization
C. Condensation
D. Solidification
E. Sublimation
F. Sublimation

### Topics Covered in Matter in our Surrounding Class 9 Science

1. Physical Nature of Matter
• MATTER IS MADE UP OF PARTICLES
• HOW SMALL ARE THESE PARTICLES OF MATTER?
2. Characteristics of Particles of Matter
• PARTICLES OF MATTER HAVE SPACE BETWEEN THEM
• PARTICLES OF MATTER ARE CONTINUOUSLY MOVING
• PARTICLES OF MATTER ATTRACT EACH OTHER
3. States of Matter
• THE SOLID STATE
• THE LIQUID STATE
• THE GASEOUS STATE
4. Can Matter Change its State?
• EFFECT OF CHANGE OF TEMPERATURE
• EFFECT OF CHANGE OF PRESSURE
5. Evaporation
• FACTORS AFFECTING EVAPORATION
• HOW DOES EVAPORATION CAUSE COOLING?