NCERT SOLUTION CLASS 9 SCIENCE PAGE-6

 NCERT SOLUTION OF CHAPTER 1 OF CBSE BOARD CLASS 9 ( MATTER IN OUR SURROUNDINGS)

PAGE NO 6

QUESTION NO 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 chimneys,honey,water,chalk,cotton and iron.

ANSWER;

   In the given substances,the increasing order of their density as follows
1. Air.
2. Exhaust from chimney.
3. Cotton
4. Water
5.Honey
6. Chalk
7. Iron

QUESTION NO 2 (a)

    Tabulate the differences in the characteristics of states of matter.

(b) Comment upon the following: rigidity,compressibility,fluidity,shape,kinetic energy and density.

ANSWER;

The differences in the characteristics of the matter are given in the following table-

Solid  State   Liquid  State  Gaseous State

1. Solid has definite   1.No definite         1.Gases have neither

shape and volume     shape                      a definite shape nor

                                                                       a definite volume.

2. Incompressible      2.Compressible     2.Highly compressible
3.There is a little        3.Liquid particles 3.The space between 

space between the     have a greater       gas particles is the

particles of solid        space compare to   greatest

                                      solid

4.The force of             4.The force of          4.The force of 

attraction among       attraction among    attraction is least  

the solid particles      liquid particles are  between the gaseous
are higher                   less than solid           particles
5.Particles of solid    5.Particles of liquid  5.Gaseous particles
cannot move              move freely                are in a continuous
freely                                                                 random motion

Answer 2 (b)

    Rigidity-------        It can be expressed as the tendency of matter to resist  a change in                                    shape.

   Compressibility------ It is the ability to reduce to a lower volume when force is                                                     applied.

   Fluidity ------            It is the ability to flow.

   By  Filling a gas container---------

   Shape------              It defines a definite boundary.

  Kinetic Energy-------- It is the energy of a particle due to its motion.

  Density----------          It is the mass per unit volume.

QUESTION NO 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: 

     (a)  There is less attraction between particles of gas. Thus gas particles move freely in all directions. Hence gas completely fills the vessel in which it is kept.

     (b) Particles of gas move randomly in all directions at high speed. As a result, the particles collide each other and also collide with the walls of container with a force. Hence gas exerts pressure on the walls of the container.

    (c) A wooden table has a definite shape and volume. It is rigid and cannot be compressed so it has the characteristics of a solid. So it is called solid.

    (d) Particles of air have large spaces between them. That's why we can easily move our hand in air. while wood has little space between the particles. It is rigid also. Because of this reason we need a karate expert to move our hand,because more force is required.

QUESTION NO 4

   Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.

ANSWER : 

 In the solid state, when water molecules come close to each other, the molecules are forced to align in a very particular structure a hexagonal lattice. It is tiny pores in which air is present. Due to increased bond angles and expanded molecular structure this implies greater volume and hence it has lower density.

         Density =  Mass/Volume

  This is the reason why ice floats on water.