🔥 Class 9 Chemistry Chapter 2: Is Matter Around Us Pure? — Easy Notes, Tricks & Important Questions!

CBSE Class 9 Chemistry – Chapter 2

Is Matter Around Us Pure?

Everything around us is made of matter. Matter can be either a pure substance or a mixture.

1. Pure Substance

A pure substance contains only one kind of particle and has a fixed composition.

Examples: Gold, copper, oxygen, distilled water and sodium chloride.

Pure substances are of two types:

• Elements – Made up of only one kind of atom.
• Compounds – Made up of two or more elements chemically combined in a fixed ratio.

2. Mixtures

A mixture contains two or more substances that are physically combined. The substances in a mixture can usually be separated by physical methods.

Examples: Air, salt water, soil and milk.

Mixtures are mainly of two types:

Homogeneous Mixture

The composition is uniform throughout the mixture.

Examples: Salt solution, sugar solution and air.

Heterogeneous Mixture

The composition is not uniform throughout the mixture.

Examples: Sand and water, oil and water, and soil.

3. Solution

A solution is a homogeneous mixture of two or more substances.

• Solute: The substance that gets dissolved.
• Solvent: The substance that dissolves the solute.
• Solution: Solute + Solvent.

Example: In salt water, salt is the solute and water is the solvent.

Concentration of a Solution

Concentration tells us how much solute is present in a given amount of solution.

Mass by mass percentage:

Mass % = (Mass of solute / Mass of solution) × 100

Mass by volume percentage:

Mass % = (Mass of solute / Volume of solution) × 100

4. Suspension

A suspension is a heterogeneous mixture in which insoluble solid particles are spread throughout a liquid.

Examples: Muddy water and chalk powder in water.

Suspension particles are large enough to be seen and can be separated by filtration. They also scatter light.

5. Colloid

A colloid is a mixture in which very small particles are spread throughout another substance.

Examples: Milk, fog, smoke and clouds.

Colloidal particles are too small to be seen easily, but they scatter a beam of light. This is called the Tyndall effect.

6. Difference Between Solution, Colloid and Suspension

Property	Solution	Colloid	Suspension
Type	Homogeneous	Heterogeneous	Heterogeneous
Particles	Very small	Intermediate	Large
Can be filtered?	No	No	Yes
Shows Tyndall effect?	No	Yes	Yes

7. Separation of Mixtures

Different methods are used to separate the components of a mixture.

• Filtration: Separates an insoluble solid from a liquid.
• Evaporation: Used to obtain a dissolved solid from a solution.
• Centrifugation: Used to separate very fine suspended particles. Example: cream from milk.
• Separating funnel: Used to separate immiscible liquids such as oil and water.
• Sublimation: Used when one substance changes directly from solid to gas. Example: ammonium chloride.
• Chromatography: Used to separate different components of a mixture, such as colours in ink.
• Distillation: Used to separate a solvent from a solution or liquids with different boiling points.
• Fractional distillation: Used to separate two or more miscible liquids having close boiling points.
• Crystallisation: Used to obtain a pure solid in the form of crystals.

8. Physical and Chemical Changes

Physical Change

A physical change does not produce a new substance.

Examples: Melting of ice, cutting paper and dissolving sugar in water.

Chemical Change

A chemical change produces one or more new substances.

Examples: Rusting of iron, burning of wood and curdling of milk.

9. Elements

An element is a pure substance made up of only one kind of atom. It cannot be broken down into simpler substances by chemical methods.

Elements are commonly classified as:

• Metals: Iron, copper, aluminium.
• Non-metals: Oxygen, sulphur, carbon.
• Metalloids: Silicon, boron.

10. Compounds

A compound is a pure substance formed when two or more elements combine chemically in a fixed ratio.

Examples: Water, carbon dioxide and sodium chloride.

The properties of a compound are different from the properties of the elements that form it.

11. Mixture vs Compound

Mixture	Compound
Substances are physically mixed.	Elements are chemically combined.
Composition can vary.	Composition is fixed.
Components retain their properties.	A new substance with new properties is formed.
Can usually be separated by physical methods.	Usually requires chemical methods for separation.

12. Important Definitions

• Pure substance: Matter containing only one kind of particle.
• Mixture: Two or more substances physically combined.
• Solute: Substance that is dissolved.
• Solvent: Substance that dissolves the solute.
• Solution: Homogeneous mixture of solute and solvent.
• Suspension: Heterogeneous mixture with large insoluble particles.
• Colloid: Mixture containing particles of intermediate size.
• Tyndall effect: Scattering of light by colloidal particles.
• Element: Pure substance made of one kind of atom.
• Compound: Pure substance formed by chemical combination of elements in a fixed ratio.

13. Quick Revision

• Matter is either a pure substance or a mixture.
• Elements and compounds are pure substances.
• Mixtures may be homogeneous or heterogeneous.
• Salt solution is a homogeneous mixture.
• Muddy water is a suspension.
• Milk is a colloid.
• Colloids show the Tyndall effect.
• Mixtures can generally be separated by physical methods.
• Compounds are formed by chemical combination.
• Elements cannot be broken down by ordinary chemical methods.

Important Questions

1. What is a pure substance?
2. What is a mixture? Give two examples.
3. Differentiate between homogeneous and heterogeneous mixtures.
4. What are solute and solvent?
5. What is a suspension?
6. What is a colloid? Give examples.
7. What is the Tyndall effect?
8. Name the methods used to separate mixtures.
9. Differentiate between a mixture and a compound.
10. What is the difference between a physical and a chemical change?

Chapter in one line: Matter around us may be pure or mixed, and different types of mixtures can be identified and separated using suitable physical methods.