Class 9 Science Chapter 2 Is Matter Around Us Pure? Notes

What is a substance?

Anything that cannot be broken into further particles by applying any physical processes is called a Substance.

What is a Matter? How many types of matter are there?

Anything which occupies space and has mass is called matter.

Matter can be classified into two types of substances – Pure substances and Mixtures

What is a pure substance?

A substance that consists of only one type of particle is called a Pure Substance. For Example, Diamond, Salt, Sulfur, Tin etc.

What is a mixture? How many types of mixture are there?

When we combine different substances into each other a mixture is formed. For Example, Lemonade is a mixture of three substances, Lemon Juice, Sugar and Water.

There are two types of mixtures :- Homogeneous Mixtures and Heterogeneous Mixtures

  1. Homogeneous mixture

A mixture that has a uniform composition throughout is called a homogeneous mixture or solution.

Examples: sugar in water, salt in water.

  1. Heterogeneous mixture

A mixture which contains physically distinct parts and has a non-uniform composition is called a heterogeneous mixture.

What is Solution?

A solution is a homogeneous mixture of two or more substances. For example Lemonade, soda water etc.

What are the properties of Solutions?

  1. Its particles are too tiny and have a diameter less than 1 nm.
  2. The particles are not visible to naked eyes.
  3. Particles do not scatter a beam of light passing through them, hence the Tyndall effect does not exist.
  4. The solute particles never settle down when kept undisturbed.
  5. The components of a solution cannot be separated by using filtration.

What are the components of Solution?

A solution has two components:

(i) Solvent

(ii) Solute

What is Solvent?

 The component of the solution that dissolves the other component in it (usually the component present in larger amount) is called the solvent. For example:- Water in the salt and water solution.

What is Solute ?

The component of the solution that is dissolved in the solvent (usually present in lesser quantity) is called the solute. For example:- salt in the salt and water solution.

What is an alloy?

An alloy is a mixture of different metals or non-metals and metals that cannot be separated from each other using physical methods. For Example:

Brass – Copper with up to 50% zinc

Bronze – Copper with up to 12% tin

What is a stable solution?

A stable solution is a solution in whose particles do not settle down if we leave the solution undisturbed for some time. This is because the particles of a stable solution are homogeneously spread.

Concentration of Solutions

What do you mean by Dilution?

 A solution in which the concentration of the solute is much less than that of the solvent.

What is Saturation Point of a Solution ?

If we keep on adding the solute in a solution there comes a point when no more solute dissolves in the solution. This is called the Saturation Point of a Solution.

What is Unsaturated Solution?

A solution, in which we can add more amount of solute as it has not achieved its saturation level yet, is called an Unsaturated Solution. A dilute solution can be called as an Unsaturated Solution.

What do you mean by Concentrated Solution?

 A solution with a large amount of solvent is called a Concentrated Solution.

What is Saturated Solution ?

A solution in which no more solute can be added since it has already dissolved the maximum amount of solute it can is called a Saturated Solution.

What are the factors Affecting Solubility?

  1. Temperature – Solubility increases with temperature. The situation is different for gases. With the increase in temperature, they became less soluble in each other and in water, but more soluble in organic solvents.
  2. Pressure – For the majority of solid and liquid solutes, pressure does not affect solubility. The solubility of gas is directly proportional to the pressure of this gas.

What is the concentration of a solution?

The concentration of a solution is the amount of solute present in a given amount (mass or volume) of solution. Also, the amount of solute dissolved in a given mass or volume of solvent is called concentration of solution.

Concentration of solution = Amount of solute/Amount of solvent (Here, amount means mass or volume).


 Amount of solute/Amount of solution (Here, amount means mass or volume).

What are the two methods of finding concentration of solution?

(i) Mass by mass percentage of a solution = (Mass of solute/Mass of solution) ×100

(ii) Mass by volume percentage of a solution = (Mass of solute/Volume of solution) ×100

What is Suspension? What are its properties?

A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium.
For example:- Chalk in water, smoke in the air

Properties of Suspension :-

1. It is a heterogeneous mixture.
2. Suspension particles are visible to the naked eye.
3. The particles are greater than 100 nanometers.
4. It is unstable mixture. Over time, the solute settles to the bottom of the container.
5.They can be separated from the mixture by the process of filtration.
6. It scatters light when light is passed through the solution.

What is Colloidal solution ? What are its properties ?

Colloid solution is heterogeneous mixture in which the size of particles lies between the true solutions and suspensions.

Properties of colloidal solution:
1. The particles of a colloidal solution cannot be seen individually with the naked eye.
2. It is a heterogeneous mixture and thus its particles can’t be separated by filter paper.
3. Particle size is smaller than that of suspensions but larger than that of solutions (1 nm to 100 nm).
4. It is a stable mixture. Particles do not settle down at the bottom over a period of time.
5. When left undisturbed, they do not settle down, showing that the colloid is quite stable.

What is Tyndall effect?

Colloidal particles can easily scatter a beam of visible light. This phenomenon is called Tyndall effect.

What are the difference between Physical and Chemical changes ?

Physical Changes

Chemical Changes

It brings about change in physical properties such as physical state, shape, size etc.


It brings about changes in chemical properties.

No changes in chemical compositions are observed.

Changes in chemical compositions are observed.

It is reversible.

It is irreversible that means permanent

No new substance is formed.

New substance is formed.