# NCERT Solutions for Class 9 Science, Chapter 1: Matter in our Surroundings

## Class 9 Science, Chapter 1: Matter in our Surroundings

Matter in our Surroundings – Class 9 is the first stepping stone for a student in the competitive world. With the introduction of the CBSE Board Exam for class 10 a few years back, this has become an important gateway for a student. Based on the results of class 9th a student selects his future stream of Science, Commerce or Arts suiting his interest.

Takshila Learning is providing NCERT Solutions for Class 9 Science as per the latest syllabus by CBSE. Class 9 is the building block for the CBSE Class 10 Board Exams, not only for your exams but also for your higher studies and career. Science is the most essential subject and the knowledge in this field opens up wider career opportunities for the students.

Below you can find the NCERT solution for Class 9th Science. You can get a Solution for the all-important question of “Matter in our Surroundings

Ques1: Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, lemon water, smell of perfume?

Answer: Chair, air, almonds, and cold drinks.

Ques 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 differential use at a very slow rate. But, if the temperature of the solid is increased, then the rate of diffusion of the solid particles into the 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 be close.

Ques 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 particles of the matter have intermolecular spaces. The intermolecular spaces in liquids is fair enough to let the diver pass through it.

Ques 4: What are the characteristics of the 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.

Intext questions (set 2)

Page no. 7

Ques 1: The mass per unit volume of a substance is called density.   (density=mass/volume). Arrange the following in the order of increasing density – air, exhaust from the chimneys, honey, water, chalk, cotton and iron.

Answer: Air, exhaust from chimneys, cotton, water, honey, Chalk, and iron.

Ques 2: Answer the following. a) Tabulate the differences in the characteristics of matter. b) Comment upon the following: rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy and density.

(a)

 Property SOLID STATE LIQUID STATE GASEOUS STATE 1 Definite shape and volume. No definite shape. Liquid 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 Particles don’t move freely Particles move freely but are confined within the boundary Particles move freely 4 Cannot flow Can flow can flow 5 Force of attraction between particles is maximum Force of attraction between particles is less than solid but more than in gas Force of attraction between particles is least.

(b)

Rigidity: it is the property of matter to resist the change of its shape.

Compress ability: it is the property of matter in which its volume is decreased by applying force.

Fluidity: it is the ability of matter to flow.

Feeling a gas container: on feeling a gas takes place the shape of the container.

Shape: having definite boundaries.

Kindly take energy: it is the energy possessed by the particles of matter due to its motion.

Density: it is the Ratio of mass with per unit volume.

Ques 3: Give reasons:

(a) A gas fills completely the vessel in which it is kept.

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

(b) A gas exerts pressure on the walls of the container.

• Particle of gas moves randomly in all directions at high speed. As a result, the particles hate 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 should be called a solid.

• I wouldn’t table has fixed shape and fixed volume, which are the main characteristics of solid. Does a wooden table could be called solid.

(d) We can easily move our hand in the air but to do the same through a solid block of wood we need a karate expert.

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

Ques 4: Liquids generally have a lower density than solids. But you must have observed that ice floats on water. Find out why.

Answer: Ice which solid has weakened spaces between water molecules thus making ice lighter than water. Thus, ice float on water.

Intext questions (set 3)

Page no. 10

Ques 1: Convert the following temperature to Celsius scale:
a. 300K          b. 573K

300K= (300-273)°C = 27°C

(b). 573K= (573-273)°C = 300°C

Ques 2: What is the physical state of water at:   a. 250°C         b. 100° C?

Answer: (a) At 250°C – Gaseous state since it is beyond its boiling point.

(b) At 100°C – It is at the transition state as the water is at its boiling point. Hence it would be present in both liquid and gaseous state.

Ques 3:  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 a release it is utilised in phase change. Such heat is called latent heat. So, the temperature of any substance remains constant during the change of state.

Ques 4: Suggest a method to liquefy atmospheric gases.

Answer: The gases can be converted into liquid by bringing the particles closer so atmospheric gases can be liquefied either by decreasing temperature or by increasing pressure.

Intext questions (set 4)

Page no. 11

Ques 1: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 evaporate. In hot and dry days the moisture level is very low in the atmosphere which increases the rate of evaporation. Because of faster evaporation, the cooler works well. That’s why desert coolers schools better on a hot dry day

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

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. In this way, water kept in an earthen pot become cool during summers.

Ques 3: Why does our palm feel cold when we put on some acetone or petrol or perfume on it?

Answer: Acetone, petrol, and perfume evaporates 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 phone cooler.

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

Answer: Liquid has a large surface area in a saucer than a cup. Does, it evaporates faster and cool faster in a saucer than a cup. Thus, we are able to sip hot tea or milk faster from a saucer than a cup.

Ques 5: What type of clothes should we wear in summer?

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

Exercises:

Page no : 13

1. Convert the following temperature to Celsius scale.
(a) 293K                (b) 470K

Answer: 0°C=273K(a) 293K= (293 – 273)°C = 20°C(b)  470K= (470 – 273)°C = 197°C

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

(a) 25°C = (25+273)K = 298K

(b) 373°C = (373+273)K = 646K

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

Answer: (a) Naphthalene balls disappear with time without leaving any solid because of the undergoes sublimation easily, the change of state of naphthalene from solid to gas takes place easily.

(b) Perfumes have high degree of vaporisation and its vapour defuses into easily. Therefore, we can get the smell of perfume sitting several metres away.

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

1. What is the physical state of water at –
(a) 25°C (b) 0°C (c) 100°C?

Answer: (a) At 25°C, the water will be in liquid form (normal room temperature)

(b) At 0°C, the water is at its freezing point, hence both solid and liquid phases are observed.

(c) At 100°C, the water is at its boiling point, hence both liquid and gaseous state of water (water vapor) are observed.

1. 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). What are 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 Almira is a solid at room temperature it has a rigid and fixed shape.

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

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

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

Answer: Steam produces severe burns. It is because it is an exothermic reaction that releases high amount of heat which it had consumed during vaporization.

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

A: Melting (or) fusion (or) liquefaction
B: Evaporation (or) vaporization
C: Condensation
D: Solidification
E: Sublimation
F: Sublimation

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