Selina ICSE Class 8 Chemistry Solutions Chapter 1 Matter

Selina ICSE Solutions


Q1. Define:
(a) Matter
(b) Intermolecular force of attraction.
(a) Anything that has mass, takes up space and can be perceived by our senses is considered to be matter. Example: Air, book.
(b) The molecules of matter are constantly moving and are held together by an attraction between them known as the intermolecular force of attraction.

Q2. What are the three states of matter? Define each of them with two examples.
The three states of matter are:
1. Solids — A solid has a definite shape and definite volume. Example – wood, stone, iron, ice etc.
2. Liquid — A liquid has a definite volume but not definite shape. Example — water, juice, milk, oil etc.
3. Gases — A gas neither has definite shape nor a definite volume. Example – air, hydrogen, oxygen, watervapour etc.

Q3. Define inter-conversion of states of matter. What are the two factors responsible for the change of states of matter?
Inter-conversion state of matter refers to the process by which a substance can transition from one state to another and back again while maintaining its chemical composition. There are two elements that cause a change in the state of a substance: temperature and pressure changes.

Q4. State the main postulates of kinetic theory of matter.
Below are the major tenets of the theory:
1. Atoms and molecules are the smallest units of matter.
2. A type of substance has identical building blocks at every level.
3. The area or gaps between these particles is referred to as the inter-particular or inter-molecular space.
4. The particles of matter are held together by an attractive force that exists between them. Inter-particular or intermolecular force of attraction is the name given to this force of attraction.
5. Matter particles always move randomly and have kinetic energy, which rises with rising temperature and falls with falling temperature.

Q5. What happens to water if
(a) it is kept in a deep freezer

(a) Water that is stored in a deep freezer cools and turns into ice at 0°C.
(b) Water heated to 100°C turns into steam.

Water’s ability to change states: Water is a liquid under normal circumstances, but when stored at 0°C in a deep freezer, it turns into ice, and when that ice is held at room temperature, it turns back into liquid water. Similar to how water, when heated to 100°C, turns into steam, which then cools and returns to liquid form. However, water’s chemical makeup remains unchanged. When it transforms from a liquid to a solid or from a liquid to a gaseous state.

Q 6. (a) State the law of conversation of mass.
(b) What do you observe when, barium chloride solution is mixed with sodium sulphate solution?
In a chemical reaction, matter cannot be generated or destroyed. It might, however, transition from one form to another throughout the process.
The phrase “In a chemical reaction, the total mass of the reactants is equal to the total mass of the products” can also be used to express this.
(a) We will see that a white, insoluble barium sulphate solid (precipitate) forms beside a sodium chloride solution. Wait ten minutes for the reaction to finish and the solid to settle. Reevaluate the content and take note of the reading.
We shall note that total apparatus mass plus reactants equals total apparatus mass plus products. Thus, the mass conservation law is supported.

Q 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.
(a) Since molecules are free to move in gases.
They do not adhere to one another, and gases have the weakest intermolecular force of attraction. As a result, the gas almost completely filled the confined vessel.
(b) Particles in solids are closely packed. The intermolecular space is virtually zero and there is a significant force of attraction. Since the molecules cannot move freely as a result, they are inflexible and hard. Solids therefore cannot be compacted.
(c) Because there is a lot of intermolecular space and the particles are less tightly packed, the intermolecular force is weaker in liquids. As a result, molecules in a liquid can travel at random and hence easily flow.
(d) After burning magnesium ribbon in the air.

Q 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.

Q 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.
(a) Camphor, iodine, naphthalene, ammonium chloride, dry ice (solid carbon dioxide), etc.
(b) Gases do not change their state on heating.
Example: O2.

Q10. Define:
(a) Diffusion
(b) Brownian motion
(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’.

Q11. 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?
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, this is because there is some space between the particles of water in which the salt particles get accommodated when dissolved.

Q12. What do you observe when a gas jar which appears empty is inverted over a gas jar containing Bromine vapours? Name the phenomenon.
When an air-filled gas jar is placed on top of a gas jar filled with reddish brown bromine vapours. It has been noticed that the reddish-brown vapours of Into the upper jar, bromine also spread. Diffusion is the term for this mingling. Amount of Diffusion occurs most quickly in gases and least quickly in solids. When there is a rise in temperature.

Q13. Why can a piece of chalk be broken easily into smaller pieces while a coal piece cannot be broken easily?
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.