Chapter 1 – Matter

Concise Chemistry 2023 solutions for class 8 Chemistry. Chapter 1 – Matter is provided here with simple step-by-step explanations. These solutions for the Matter are extremely popular among class 10 students. The Matter solution comes in handy for quickly completing your homework and preparing for exams.

Question 1

Define :

1. matter
2. intermolecular forces of attraction

Answer

1. Anything that has mass occupies volume is matter. It is composed of molecules.
2. The force of attraction between the molecules of matter is called the intermolecular force of attraction. It is maximum in solids, less in liquid and least in gases.

Question 2

What are the three states of matter? Define each of them with two examples.

Answer

The three states of matter are defined with two examples for each:

1. Solid: A solid is a state of matter in which the particles are tightly packed and have a fixed shape and volume. The particles in a solid vibrate around a fixed position but do not move around freely. Examples of solids include:

• Ice
• Wood

2. Liquid: A liquid is a state of matter in which the particles are still close together but can move around freely to take the shape of their container. A liquid has a fixed volume but no fixed shape. Examples of liquids include:

• Water
• Milk

3. Gas: A gas is a state of matter in which the particles are far apart and move around freely, colliding with each other and the walls of their container. A gas has no fixed shape or volume. Examples of gases include:

• Oxygen
• Carbon dioxide

Question 3

Define the interconversion of states of matter. What are the two factors responsible for the change of state of matter?

Answer

The interconversion of states of matter refers to the process of changing one state of matter to another. This can occur through either heating or cooling a substance, or changing the pressure it is under.

The two factors responsible for the change of state of matter are:

1. Heat energy
2. Pressure

Question 4

State the main postulates of the kinetic theory of matter.

Answer

Postulates of the kinetic theory of gases :

• Gases are composed of minute discrete particles called molecules.
• The molecules of a gas are in random motion.
• The temperature of gas is the average kinetic energy of the molecules of the gas in a system.
• The molecules of gas are supposed to be perfectly elastic.

Question 5

What happens to water if

1. it is kept in a deep freezer?
2. it is heated?

Explain the phenomenon of change of state of water.

Answer

1. If water is kept in a deep freezer, it will lose heat energy to its surroundings and the temperature will drop below the freezing point of water, causing it to change from a liquid to a solid state.
2. If water is heated, it will gain heat energy, causing its temperature to rise. If the temperature rises to the boiling point of water, the water will change from a liquid to a gaseous state, called steam.

The phenomenon of change of state of water is caused by the gain or loss of heat energy, which affects the movement of water molecules. As heat energy is added or removed, the intermolecular forces between water molecules change, causing the water to change from one state of matter to another.

Question 6

1. State the law of conservation of mass.
2. What do you observe when barium chloride solution is mixed with sodium sulphate solution?

Answer

1. The law of conservation of mass states that in any chemical reaction, the total mass of the reactants is equal to the total mass of the products.
2. When barium chloride solution is mixed with sodium sulphate solution, a white precipitate of barium sulphate is formed. This is because barium sulphate is insoluble in water, and so it precipitates out of the solution. The reaction can be represented by the chemical equation:

BaCl₂ (aq) + Na₂SO₄ (aq) → BaSO₄ (s) + 2NaCl (aq)

Question 7

Give reasons:

1. A gas can fill the whole vessel in which it is enclosed.
2. Solids cannot be compressed.
3. Liquids can flow.
4. When magnesium is burnt in air, there is an increase in mass after the reaction.

Answer

1. A gas can fill the whole vessel in which it is enclosed because the particles in a gas are very far apart and move around randomly, colliding with each other and the walls of their container. This allows a gas to spread out and fill the entire volume of its container.
2. Solids cannot be compressed because their particles are tightly packed and have very little space between them. This means that when a force is applied to a solid, the particles cannot move closer together, and the solid does not compress.
3. Liquids can flow because their particles have more space between them than solids, allowing them to move past each other and take the shape of their container. However, liquids still have strong enough intermolecular forces to maintain a fixed volume, unlike gases.
4. When magnesium is burnt in air, there is an increase in mass after the reaction because magnesium reacts with oxygen to form magnesium oxide, which has a greater mass than the magnesium and oxygen that reacted. This increase in mass is due to the oxygen from the air combining with the magnesium to form the magnesium oxide, and is in accordance with the law of conservation of mass.

Question 8

Fill in the blanks:

1. The change of a solid into a liquid is called ____
2. The process in which a solid directly changes into gas is called ____
3. The change of water vapour into water is called ____
4. The temperature at which a liquid starts changing into its vapour state is ____

Answer

1. melting
2. sublimation
3. condensation
4. boiling point

Question 9

Give two examples for each of the following:

1. The substances which sublime.
2. The substances which do not change their state on heating.

Answer

Two examples of substances which sublime are:

1. Dry ice (solid carbon dioxide)
2. Iodine crystals

Two examples of substances which do not change their state on heating are:

1. Sodium chloride (common table salt)
2. Diamond

Question 10

Define :

1. Diffusion.
2. Brownian motion.

Answer

1. Diffusion is the process by which molecules move from an area where they are more concentrated to an area where they are less concentrated, until they are evenly distributed.
2. Brownian motion is the random movement of tiny particles suspended in a fluid, caused by the collision of fluid molecules with the particles.

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

When sodium chloride dissolves in water, the dissolved particles fit into the spaces between the water molecules without increasing the volume of the water. Hence, there is no increase in the level of water.

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 which appears empty is inverted over a gas jar containing Bromine vapors, the gas in the jar will turn reddish-brown in color due to the absorption of Bromine vapors.

This is due to the phenomenon of gas absorption, where the colorless and odorless gas in the jar absorbs the visible and coloured Bromine vapours.

Question 13

Why can a piece of chalk be broken easily into smaller pieces while a coal piece cannot be broken easily? 

Answer

The strength of this force of attraction is lesser in chalk, hence it could be broken easily into smaller pieces. But the strength of the intermolecular force of attraction is very strong in coal. therefore it is not possible to break them into small pieces.