NCERT Solution Science Class 9 Matter in our Surroundings
In this page we have NCERT (intext and Exercise) solutions for Class 9 Chapter 1 Matter in our Surroundings . Hope you like them and do not forget to like , social share and comment at the end of the page.
NCERT intext Solution
Page 3
Question 1
Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, cold drink, smell of perfume. Answer
The matter are Chair, air, almonds and cold drink
Question 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 diffuse at a very slow rate. But, if the temperature of the solid is increased, then the rate of diffusion of the solid particles into 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 go close.
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 matter is made of particles and particles of matter have intermolecular spaces.
Question 4
What are the characteristics of particles of matter? Answer
The characteristics of particles of matter are:
(a) Particles of matter have spaces between them.
(b) Particles of matter are continuously moving.
(c) Particles of matter attract each other.
Page 6 Question 1
The mass per unit volume of a substance is called density ($\text {density} =\frac {\text{mass}}{\text{volume}}$).
Arrange the following in order of increasing density - air, exhaust from chimney, honey, water, chalk, cotton, and iron. Answer
We know from definition of density, gas would have least density, liquid would in between and solid will have highest density. So keeping these in mind, order of increasing density will be
air < Exhaust from chimneys < cotton < water < honey < chalk < 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)
(b)
Question 3 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. Answer
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 thus making ice lighter than water. Thus ice floats on water.
Page 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
250°C : Gaseous State (As Boiling temperature of water is 100° C).
100°C :Since water boils at this temperature thus it can exist in both liquid and gaseous form. At this temperature, after getting the heat equal to the latent heat of vaporization, 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 of any substance, the heat supplied or released is utilized in phase change. Such heat is called latent heat. So, the temperature of any substance remains constant during the change of state.
Question 4
Suggest a method to liquefy atmospheric gases. Answer
The gases can be converted into liquids by decreasing temperature or by increasing pressure.
Page 10 Question 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 evaporates. In hot and dry days the moisture level is very low in atmosphere which increases the rate of evaporation. Because of faster evaporation, cooler works well. That’s why desert cooler cool better on a hot dry day.
Question 2
How does water kept in an earthen pot (matka) become cool during summers? 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 this way, 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, thereby making the palm cooler.
Question 4
Why are we able to sip hot tea or milk faster from a saucer than a cup? Answer
A liquid has a larger surface area in a saucer than in a cup. Thus, it evaporates faster and cools faster 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 summers? Answer
We should wear cotton clothes in summers as cotton is a good sweat absorber. Sweat is absorbed by the cotton and is exposed to the atmosphere making evaporation faster. During this evaporation, particles on the surface of the liquid gain energy from our body surface, making the body cool.
NCERT Exercise Solutions
Question 1
Convert the following temperatures 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
Convert the following temperatures to Kelvin scale.
(a) 25°C
(b) 373°C
Answer
(a) 25 °C = (25 + 273) K
= 298 K
(b) 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 meters 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 has high degree of vaporization and its vapour diffuse into air easily. Therefore, we can get the smell of perfume sitting several metre away.
Question 4
Arrange the following substances in increasing order of forces of attraction between particles-- water, sugar, 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
25°C : Liquid State
0°C : Solid State or liquid state .
100°C : Gaseous State, can also be in liquid state
Question 6 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) Water 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 almirah is a solid at room temperature it has rigid and fixed shape.
Question 7
Why is ice at 273 K more effective in cooling than water at the same temperature? Answer
Ice at 273 K has less energy than water (although both are at the same temperature). Water possesses the additional latent heat of fusion. 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 has more energy than boiling water. It possesses the additional latent heat of vaporization. Therefore, burns produced by steam are more severe than those produced by boiling water.
Question 9
Name A, B, C, D, E and F in the following diagram showing change in its state. Answer
A -> Fusion
B-> Vaporization
C->Condensation
D-> Solidification
E->Sublimation
F-> Sublimation
Summary
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