NCERT Solutions for Class 9 Science Chapter 1 Matter in Our Surroundings
1. Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, lemon water, smell of perfume.
Solution:
The following substances are matter:
Chair
Air
Almonds
Lemon water
Smell of perfume (Smell is considered as a matter due to the presence of some volatile substances in air that occupy space & have mass.)
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.
Solution:
Particles in the air, if fueled with higher temperatures, acquire high kinetic energy which aids them to move fast over a stretch. Hence the smell of hot sizzling food reaches a person even at a distance of several meters.
3. A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?
Solution:
The diver is able to easily cut through the water in the swimming pool because of the weak forces of attraction between water molecules. It is this property of water that attributes to easy diving.
4. What are the characteristics of the particles of matter?
Solution:
The characteristics of particles of matter are:
(a) Presence of intermolecular spaces between particles
(b) Particles are in constant motion
(c) They attract each other
(d) All matter is composed of very small particles which can exist independently.
5. 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.
Solution:
The following substances are arranged in the increasing density:
Air
Exhaust from chimney
Cotton
Water
Honey
Chalk
Iron
6. 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.
Solution:
(a) The difference in the characteristics of the three states of matter.
Characteristics |
Solid |
Liquid |
Gas |
Shape |
Fixed shape |
No Fixed shape |
No Fixed shape |
Volume |
Fixed volume |
Fixed volume |
No Fixed volume |
Intermolecular force |
Maximum |
Less than solids |
Very less |
Intermolecular space |
Very less |
More than solids |
maximum |
Rigidity/Fluidity |
Rigid/cannot flow |
Can flow/not rigid |
Can flow/not rigid |
Compressibility |
negligible |
|
Highly compressible |
(b)
(i) Rigidity: It is the property of matter to continue to remain in its shape when treated with an external force.
(ii) Compressibility: It is the attribute of the particles to contract its intermolecular space when exposed to an external force thereby escalating its density.
(iii) Fluidity: It is the ability of a substance to flow or move about freely.
(iv) Filling the gas container: The particles in a container take its shape as they randomly vibrate in all possible directions.
(v) Shape: It is the definite structure of an object within an external boundary
(vi) Kinetic energy: Motion allows particles to possess energy which is referred to as kinetic energy. The increasing order of kinetic energy possessed by various states of matter are:
Solids < Liquids < Gases
Mathematically, it can be expressed as K.E = 1/2 mv2, where ‘m’ is the mass and ‘v’ is the velocity
of the particle.
(vii) Density: It is the mass of a unit volume of a substance. It is expressed as:
d = M/V, where ‘d’ is the density, ‘M’ is the mass and ‘V’ is the volume of the substance
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 the air but to do the same through a solid block of wood we need a karate expert.
Solution:
(a) There is a low force of attraction between gas particles. The particles in the filled vessel are free to move about.
(b) Gaseous particles have the weakest attraction force. They are always moving in a haphazard manner. When a gas particle collides with the container’s walls, it exerts force and thus pressure on the wall.
(c) There is a distinct contour and volume to the hardwood table. The wood particles are tightly packed. They do not conform to the container’s shape. As a result, the solid features of a hardwood table are satisfied.
(d) The boundaries between air particles are quite loose. They are a long way apart and have a lot of space between them. As a result, we may move our hands freely in the air. The particles in a solid block, on the other hand, are bound together by a strong force of attraction. As a result, there is either some or no space between them. As a result, we’ll require a karate expert.
8. Liquids generally have a lower density than solids. But you must have observed that ice floats on water. Find out why.
Solution:
In general, the volume of a liquid is more than the volume of a solid because liquid particles are more free to move, resulting in more volume. Ice, on the other hand, has a maximum density of water at 4 degrees Celsius. Ice is lighter than water and has a lower density. As a result, it floats on water.