RBSE Solutions for Class 9 Science Chapter 1 Matter in Our Surroundings

Rajasthan Board RBSE Solutions for Class 9 Science Chapter 1 Matter in Our Surroundings Textbook Exercise Questions and Answers.

RBSE Class 9 Science Solutions Chapter 1 Matter in Our Surroundings

RBSE Class 9 Science Chapter 1 Matter in Our Surroundings InText Questions and Answers

Page No. 3

Question 1.
Which of the following are matter?
Chair, air, love, smell, hate, almond, thought, cold, lemon water, smell of perfume.
Answer:
Anything that occupies space and has mass is called matter. Matter can exist in three physical states-solid, liquid and gaseous. 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 feelings that do not have mass and don’t occupy space.

Question 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.
Answer:
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.

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 intermolecular space is high in liquid. So, the diver can easily pass through it.

Question 4.
What are the characteristics of particles of matter?
Answer:
The characteristics of particles of matter are :

• Particles of matter have spaces between them.
• Particles of matter are continuously moving.
• Particles of matter attract each other.

Page No.6

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

Question 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.
Answer:
(a) Differences in the characteristics of states of matter :

(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.

Question 3.
Give reasons :
(a) A gas fills completely the vessel in which it is kept.
Answer:
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) A gas exerts pressure on the walls of the container.
Answer:
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 should be called a solid.
Answer:
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) 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:
In air, the inter-particle attractive forces are negligible and hence, it is easy to separate the particles in air and we can easily move our hand in air. The inter-particle forces are very strong in solids. So, it is not easy to separate the particles and it is not easy to move our hand through a solid block of wood.

Question 4.
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 making ice lighter than water. Thus, ice floats on water.

Page No. 9

Question 1.
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 2.
What is the physical state of water at :
(a) 250°C
(b) 100°C?
Answer:
(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 vaporisation, water starts changing from liquid state to gaseous state.

Question 3.
For any substance, why does the temperature remain constant during the change of state?
Answer:
During the change of state the temperature of any substance remains constant. Because heat supplied or released is utilised 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.

Question 4.
Suggest a method to liquify atmospheric gases.
Answer:
The gases can be converted into liquid if high pressure is applied at low temperature.

Page No. 10

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

Question 2.
How does water kept in an earthen pot (matka) become cool during summer?
Answer:
The liquid inside the pot evaporates through the pores in an earthen pot. This evaporation makes the water cool inside the pot. Thus, water kept in an earthen pot becomes cool during summers.

Question 3.
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 by making the palm cooler.

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

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

RBSE Class 9 Science Chapter 1 Matter in Our Surroundings Textbook Questions and Answers

Question 1.
Convert the following temperatures to Celsius scale.
(a) 293 K
(b) 470 K
Answer:
(a) 293 K.
293 K = (293 – 273)°C = 20°C

(b) 470 K
470 K = (470 – 273)°C = 197°C

Question 2.
Convert the following temperatures to Kelvin scale.
(a) 25°C
(b) 373°C
Answer:
(a) 25°C
25°C = (25 + 273) K = 298 K

(b) 373°C
373°C = (373 + 273) K = 646 K.

Question 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.
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 have high degree of vaporisation and its vapour diffuse into air easily.
Therefore, we can get the smell of perfume sitting several metres away.

Question 4.
Arrange the following substances in increasing order of forces of attraction between particles – water, sugar, and oxygen.
Answer:
Oxygen, water, sugar.

Question 5.
What is the physical state of water at :
(a) 25°C
(b) 0°C
(c) 100°C?
Answer:
(a) Liquid state
(b) At 0°C, water can exist 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 vaporisation, water starts changing from its liquid state to its gaseous state, i.e. water vapours.

Question 6.
Give two reasons to justify
(a) Water at room temperature is a liquid.
Answer:

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.
Answer:

1. Intermolecular forces are very strong.
2. Intermolecular spaces, as well as kinetic energy, are very negligible.

Thus, the molecules are held very tightly, and this results into the iron almirah has a definite shape and definite volume, and hence, is a solid.

Question 7.
Why is ice at 273 K more effective in cooling than water at the same temperature?
Answer:
Ice at 273 Khas less energy than water (although both are at the same temperature).
Since, ice can easily absorb energy from the surrounding in the form of latent heat to become water whereas water has no such advantage. Hence, at 273 K, ice is more effective in cooling than water.

Question 8.
What produces more severe burns, boiling water or steam?
Answer:
Steam will produce more severe burns than boiling water. As steam has 2260 J of heat energy (latent heat of vaporisation) as compared to boiling water. Thus, steam produces more severe burns.

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

Answer:
A – Fusion,
C – Condensation,
E – Sublimation,
B – Vaporisation,
D – Solidification,
F – Deposition