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Matter in Our Surroundings - class 9 science Textbook solutions

 Matter in Our Surroundings

1.Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, drink, smell of perfume
Chair, air, smell, almonds, cold, colddrink, smell of perfume are matter.

2.Give reasons for the following observation:
The smell hot sizzling food reaches you several metres away, but to get the smell from cold food you have to go close.
When food is hot, diffusion is more. But in cold food diffusion is slow. Hence to get the smell from cold food we have to go close.

3.A driver is able to cut through water in a swimming pool. Which property of matter does this observation show?
This observation shows that particles of matter have kinetic energy.

4.What are the characteristics of the particles of matter?
The characteristics of particles are as follows:
1.    Particles of matter have space 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 chimneys, honey, water, chalk, cotton and iron.

air, water, exhaust from chimneys, chalk, cotton, honey, iron.

6.(a) Tabulate the differences in the characteristics of state of matter.
(b) Comment upon the following: rigidity, compressibility, fluidity filling a gas container, shape, kinetic energy and density.
(a) Differences in the characteristics of states of matter
Solids    Liquids    Gases
Solids have definite shape and fixed volumes.    Liquids have no fixed shape but have a fixed volume.    In the gaseous state, the particles move about randomly, at high speed and they have more space between particles.
1.    Rigidity: The condition which do not alters the shape of solids.
2.    Compressibility: Compressing particles of gases is called compressiblity.
3.    filling a gas container: In the laboratory, after the preparation of gases, they are collected in gas jar. This is called filling a gas container.
4.    Fludity: Fluidity means flowing of liquids freely.
5.    Shape: Things are in which form is called shape.
6.    Kinetic energy: The energy possessed by moving body is called kinestic energy.
7.    Density: Density is the mass per unit
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.

(a) Because gas occupies space.
(b) Because in the gaseous state, the particles move about randomly at high speed. Due to this random movement, the particles hit each other and also the walls of the container. The pressure exerted by the gas is because of this force exerted by gas particles per unit area on the walls of the container.
(c) Because in the wooden table particles are closely packed and have less space in between particles.
(d) Air is a gas, it has more space in between particles. But solid block of wood is rigid, hence it is difficult to move our hands through it.

8.Liquids generally have lower density as compared to solids. But you must have observed that ice Boots on water. Find out why?
Density of ice is lesser than water. Hence ice floats on water.

9.Convert the following temperature to Celsius scale.
(a) 300 K
(b) 573K
(a) 300 – 273
= 27° C
∴ 300K means 27° C.
(b) 573 K
573 – 273 = 300° C
∴ 573K means 300° C.

10.What is the physical state of water at:
(a) 250° C
(b) 100° C
(a) Water changes to water vapour at 250° C temperature
(b) Water changes to water vapour at 100°C.

11.For any substance, why does the temperature remain constant during the change of state?
Because with the increase of temperature, more number of particles get enough kinetic energy to go into the vapour state. Hence temperature remains constant during the change of state.

12.Suggest a method to liquefy atmospheric gases.
L.P.G. which is used for cooking. In the cylinder petrol is in liquid form. When it is lighted it becomes gas.

13.Why does a desert cooler cool better on a hot dry day?
The particles of liquid in desert cooler absorb energy from the surrounding to regain the energy lost during evaporation. In summer this is fast. Hence desert cooler cool better in a hot dry day.

14.How does the water kept in an earthen pot (matka) become cool during summer?
Water looses its temperature through small pores present in the pot. Hence in an earthen pot (matka) become cool during summer.

15.Why does our palm feel cold when we put some acetone or petrol or perfume on it?
Because acetone or petrol or perfume looses their temperature and gain energy by using from surrounding air.

16.Why are we able to sip hot tea or milk faster from a saucer rather than a cup.
Because in a saucer, the surface is broad comparing to cup and here rate of evaporation is greater. Hence we are able to sip hot tea or milk faster from a saucer rather than a cup.

17.What type of clothes should we wear in summer?
During summer we should wear cotton clothes because cotton absorbs heat quickly and evaporate and helps to cool our body.

1.Convert the following temperatures to the Celsius scale.
(a). 293 K
(b). 470 K
(a) 293K – 273K = 20° C
(b) 470 K – 273 K = 197° C.

2.Convert the following temperatures to the Kelvin scale.
a) 25° C
b) 373° C
a) 25° C
= 25°+ 273
= 298 K
b) 373° C
= 373 + 273
= 646K.

3.Give a 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.
a) Because Naphthalene changes its state from solid to gaseous matter. Hence it disappears with time without leaving any solid,
b) Because of particles of perfumes diffuse in the air with higher speed and reaches our nose.

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

5.What is the physical state of water- at
a) 25° C
b) Q° C
c) 100° C
a) 25° C – liquid state
b) 0° C – Ice
c) 100° C – water vapour.

6.Give two reasons to justify-
a. Water at room temperature is liquid.
b. an iron almirah is a solid at room temperature.
1.    Temperature of the room is lesser, so there is no change of state of water, hence it is liquid at room temperature,
2.    Pressure is low.
1.    Temperature is less,
2.    Pressure is low.

7.Why is ice at 273 k. More effective in cooling than water at the same temperature?
Because at 0° C (273 K) particles of water have more energy comparing it to water at the same temperature.

8.What produces more severe burns, boiling water or steam.
Steam causes severe burns comparing to boiling water or steam.

9.Name A, B, C, D, E and F the following diagram showing the change in its state.
A] Indicates heating
B] Indicates heating
C] Indicates cooling
D] Indicates cooling.
E] Indicates sublimation.
F] Indicates sublimation.

Additional Questions and Answers

1.Why should we wear cotton clothes in summer?
Answer :
Cotton is a good absorber of water helps in absorbing the sweat and exposing it to the atmosphere for easy evaporation.

2.Mention the advantages of CNG.
Answer :
Due to high compressibility, large volumes of a gas can be compressed into a small cylinder and transported easily.

3.Why do we see water droplets on the outer surface of a glass containing ice-cold water?
Answer :
The water vapor present in air on coming in contact with the cold glass of water. It loses energy and gets converted to the liquid state.

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