Selina Concise Chemistry Class 8 ICSE Solutions – Matter

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Selina Concise Chemistry Class 8 ICSE Solutions – Matter

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APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 1 Matter. You can download the Selina Concise Chemistry ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Chemistry for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

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Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 1 Matter

Exercise

Question 1.
Define:
(a) matter
(b) intermolecular force of attraction.
Answer:
(a) Matter is anything which has mass, occupies space and can be percieved by our senses.
Example: Air, Book.
(b) The molecules of matter are always in motion and attract each other with a force called intermolecular force of attraction due to which they are held together.

Question 2.
What are the three states of matter ? Define each of them with two examples.
Answer:
The three states of matter are:
solids, liquids and gases

  • Solids — A solid has a definite shape and definite volume.
    Example – wood, stone, iron, ice etc.
  • Liquid — A liquid has a definite volume but not definite shape.
    Example — water, juice, milk, oil, etc.
  • Gases — A gas neither has definite shape nor a definite volume.
    Example – air, hydrogen, oxygen, watervapour etc.

Question 3.
Define interconversion of states of matter. What are the two factors responsible for the change of states of matter?
Answer:
The process by which matter changes from one state to another and back to original state, without any change in its chemical composition is called interconversion state of matter.
Two factors responsible for change of state of matter are: change in
(i) Temperature (ii) Pressure

Question 4.
State the main postulates of kinetic theory of matter.
Answer:
The main postulates of the theory are:

  1. Matter is composed of very small particles called atoms and molecules.
  2. The constituent particles of a kind of matter are identical in all respects.
  3. These particles have space or gaps between them which is known as interparticular or intermolecular space.
  4. There exists a force of attraction between the particles of matter which holds them together. This force of attraction is known as interparticular or intermolecular force of attraction.
  5. Particles of matter are always in a state of random motion and possess kinetic energy, which increases with increase in temperature and vice-versa.

Question 5.
What happens to water if
(a) it is kept in a deep freezer
(b) it is heated
Explain the phenomenon of change of state of water.
Answer:
(a) When water is kept in a deep freezer, it gets cooled and change into ice at 0°C ice.
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(b) Water on heating changes into steam at 100°C
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Phenomenon of change of state of water:
Water is a liquid under ordinary conditions but, when it is kept in a deep freezer, it changes into ice at 0°C and when ice is kept at room temperature again changes back into liquid water.
Similarly, water on heating change into steam at 100°C, which on cooling changes back into liquid water. But there is no change in the chemical composition of water. When its state changes from liquid to solid or liquid to gaseous state.
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Question 6.
(a) State the law of conversation of mass.
(b) What do you observe when, barium chloride solution is mixed with sodium sulphate solution ?
Answer:
(a) “Matter can neither be created nor be destroyed in a chemical reaction”. However, it may change from one form to another in the process.
It can also be stated as, “In a chemical reaction, the total mass of the reactants is equal to the total mass of the products”.

(b)
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We will observe that a white insoluble solid (precipitate) of barium sulphate is formed along with a solution of sodium chloride. Wait for ten minutes to complete the reaction and the solid formed to settle down.
Weigh the content again and note the reading.
We will observe that,
total mass of the apparatus + reactants = total mass of apparatus + products
Hence the law of conservation of mass is verified.

Question 7.
Give reasons:
(a) A gas can fill the whole vessel in which it is enclosed.
(b) Solids cannot be compressed.
(c) Liquids can flow.
(d) When magnesium is burnt in air, there is an increase in mass after the reaction.
Answer:
(a) Because, in gases, the molecules are free to move.
They are not stuck to each other and the intermolecular force of attraction is least in the gases. So the gas almost filled the whole vessel in which it is enclosed.

(b) In solids, particles are closely packed. There is a strong force of attraction and the intermolecular space is almost zero. Therefore the molecules are not free to move, which makes them hard and rigid. So solids can not be compressed.

(c) In liquids intermolecular force is weaker because the particles are not closely packed and hence there is large intermolecular space. So molecules in a liquids can move randomely and hence liquids can flow easily.

(d) When magnesium ribbon is burnt in air, a white solid, magnesium oxide is formed. The mass of magnesium oxide is
more than the mass of magnesium. This is because mass of oxygen used is not taken. If that is considered, the total mass of the reactants and the products is found to be almost equal.
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Question 8.
Fill in the blanks:

(a) The change of a solid into a liquid is called melting or fusion.
(b) The process in which a solid directly changes into a gas is called sublimation.
(c) The change of water vapour into water is called condensation.
(d) The temperature at which a liquid starts changing into its vapour state is evaporation or vaporisation.

Question 9.
Give two examples for each of the following:
(a) The substances which sublime.
(b) The substances which do not change their state on heating.
Answer:
(a) Camphor, iodine, naphthalene, ammonium chloride, dry ice (solid carbon dioxide), etc.
(b) Gases do not change their state on heating.
Example: O2.

Question 10.
Define:
(a) Diffusion.
(b) Brownian motion.
Answer:
(a) Diffusion: The intermixing of two or more substances due to the motion of their particles in order to get a uniform mixture is called ‘diffusion’.
(b) Brownian motion: The haphazard, random motion of suspended particles on the surface of a liquid or in air is called ‘Brownian motion’.

Question 11.
When sodium chloride is added to a definite volume of water and stirred well, a solution is formed, but there is no increase in the level of water. Why?
Answer:
This is because there is some space between the particles of water in which the salt particles get accomodated when dissolved.

Question 12.
What do you observe when a gas jar which appears empty is inverted over a gas jar containing Bromine vapours? Name the phenomenon.
Answer:
When a gas jar full of bromine vapours (reddish brown) is inverted over a gas jar containing air over it. It is observed that after sometime, the reddish brown vapours of bromine also spread out into the upper jar. This mixing is called diffusion. The rate of diffusion is the fastest in gases and the slowest in solids. It increases with an increase in temperature.

Question 13.
Why can a piece of chalk be broken easily into smaller pieces while a coal piece cannot be broken easily?
Answer:
The particles of matter have force acting between them. This force keeps the particles together. The strength of this force of attraction is lesser in chalk, hence it could be broken easily into smaller pieces.
But the strength of inter-molecular force of attraction is very strong in coal, therefore it is not possible to break them into small pieces.

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