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

 Chapter Name NCERT Solutions for Class 9 Science Chapter 1 Matter in Our Surroundings Topics Covered NCERT Intext QuestionsNCERT Exercise Solutions Related Study NCERT Solutions for Class 9 ScienceNCERT Revision Notes for Class 9 ScienceImportant Questions for Class 9 ScienceMCQ for Class 9 ScienceNCERT Exemplar Questions For Class 9 Science

### NCERT Intext Questions

1. Which of the following are matter?
Chair, air, love, smell, hate, almond, thought, cold, lemon water, smell of perfume.

Solution

Anything that occpics space and has mass is called matter. Matter can exist in three physical states solid, liquid and gasseous. Chair and almond are forms of matter in solid state. Cold drink is a liquid state of matter. Air and smell of perfume, are gaseous states of matter. Love, smell, cold are not matter, as they are feeling that do not have mass and don’t occupy space.

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 food particles diffuse faster in air when temperature is high and we can smell it earlier, whereas cold food particles take time to diffuse so we have to go close to smell it.

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 particles of matter?

Solution

The characteristics of particles of matter are :

1. Particles of matter have spaces between them.
2. Particles of matter are continuously moving.
3. Particles of matter attract each other.

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.

Air, exhaust from chimney, cotton, water, honey, chalk, and iron.
(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) Differences in the characteristics of states of matter :

 Property Solid Liquid Gas Rigidity Rigid and cannot be compressed Not rigid and can be compressed to a little extent. Not rigid and can be easily compressed Shape Definite shape Shape of container No definite shape Volume Definite volume Definite volume No definite volume Fluidity Cannot flow Can flow from higher to lower level Flow in all direction Diffusion Almost nil Diffuse slowly Diffuse easily Storage Can be stored without container Open/closed container is needed. Only closed container can store Inter – molecular space Least Greater than solid but lesser than gases Maximum Arrangement of molecules Regular, close to each other Random or irregular close to each other Random and wide apart Movement of molecules Very little movement in the form of vibrations Molecules can move around each other Quick movement in random direction Strength of bond between molecules Strong bond Weak bond Very loose bonding Examples A rock Water Water vapour

(b) (i) Rigidity : It is the property of matter to counter the change of its shape.
(ii) Compressibility : It is the property of matter in which its volume is decreased by applying force.
(iii) Fluidity : It is the ability of matter to flow.
(iv) Filling a gas container : On filling a gas or liquid, it takes the shape of the container.
(v) Shape : A shape is the form of an object or its external boundary.
(vi) Kinetic energy : The kinetic energy of an object is the energy that is due to its motion.
(vii) Density : Density of a substance is its mass per unit volume.

6. 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) 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.

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

Solution

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

8. Convert the following temperature to Celsius scale :
(a) 300 K
(b) 573 K

Solution

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

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

Solution

(a) Gaseous state at 250°C.
(b) Equilibrium state between liquid and vapour (100°C). At this temperature, after getting the heat equal to the latent heat of vaporization, water starts changing from liquid state to gaseous state.

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

Solution

During the change of state the temperature of any substance remains constant. Because heat supplied or released is utilized in changing the state by overcoming the forces of attraction between the particles. Therefore, this heat does not contribute in increasing or decreasing the temperature of the substance. Such heat is called latent heat.

11. Suggest a method to liquify atmospheric gases.

Solution

The gases can be converted into liquid if high pressure is applied at low temperature.

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

Solution

There is high temperature and low humidity in day time in desert. These factors increase evaporation, and cooler works well because of faster evaporation. This also means that desert cooler cool better on a hot dry day.

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

Solution

The liquid inside the pot evaporates through the pores in an earthen pot. This evaporation makes the water inside the pot cool. Thus, water kept in an earthen pot becomes cool during summers.

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

Solution

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, so making the palm cooler.

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

Solution

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

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

Solution

We should wear cotton clothes in summer as cotton is a good water (sweat) absorber. Sweat is absorbed by the cotton and it exposes water to the atmosphere for evaporation to make the body cool.

### NCERT Exercises Solutions

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

Solution

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

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

Solution

(a) 25°C = (25 + 273) K = 298 K
(b) 373°C = (373 + 273) K = 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) Naphthalene balls disappear with time without leaving any solid because they undergoes sublimation easily, i.e. the change of state of naphthalene from solid to gas takes place easily.
(b) Perfumes have high degree of vaporization and its vapour diffuse into air easily. Therefore, we can get the smell of perfume sitting several metres away.

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

Solution

Oxygen, water, sugar.

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

Solution

(a) Liquid state
(b) At 0°C, water can exits as both solid and liquid. At this temperature, after getting the heat equal to the latent heat of fusion, the solid form of water, i.e. ice starts changing into its liquid form, i.e. water.
(c) At 100°C, water can exist as both liquid and gas. At this temperature, after getting the heat equal to the latent heat of vaporization, water starts changing from its liquid state to its gascons state, i.e. water vapours.

6 Give two reasons to justify —
(a) Water at room temperature is a liquid.
(b) An iron almirah is a solid at room temperature.

Solution

(a) Water at room temperature is a liquid because:

1. Intermolecular forces are less.
2. Intermolecular spaces and kinetic energy is more.
Thus, the molecules of water can interchange their spaces and hence water is in liquid state at room temperature.

(b) An iron almirah is a solid at room temperature because:

1. Intermolecular forces are very strong.
2. Intermolecular spaces, as well as, kinetic energy are very small.
Thus, the molecules are held very very tightly, with the result, the iron almirah has a definite shape and definite volume, and hence, is a solid.

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

Solution

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

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

Solution

Steam will produce more severe burns than boiling water. As steam has 2260 J of heat energy (latent heat of vaporization) as compared to water. Thus, steam produces more severe burns.

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

Solution