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

CBSE Class 9 Science Notes Chapter 2 Matter Around Us Pure

Matter is composed of two or more components known as substances. In science, a substance is a form of matter that cannot be separated into other forms by physical means. A "pure substance" refers to only one component, with no other mixed substances. When different substances are combined, the result is called a mixture.

1.0Download Class 9 Science Notes Chapter 2 Matter Around Us Pure: Free PDF

Students can now download free PDF notes for CBSE Class 9 Science Chapter 2, Is Matter Around Us Pure, created to simplify concepts and enhance learning. These notes provide a clear understanding of mixtures, compounds, types of solutions, and various methods of separation used in daily life and industries.

Class 9 Science Chapter 2 Revision Notes:

2.0Chemical Classification of Matter

Matter around us can be classified into pure substances and mixtures based on its chemical nature

Chemical classification of matter

Pure Substances

A pure substance consists of only one type of particle and is divided into:

  • Elements: Substances that cannot be broken down into simpler substances. Examples include oxygen, gold, and hydrogen.
  • Compounds: Substances formed by combining two or more elements in fixed ratios. Examples include water (H₂O) and salt (NaCl).

Mixtures

Mixtures contain two or more pure substances physically combined, retaining their individual properties:

  • Homogeneous Mixtures: Have a uniform composition throughout, like saltwater or air.
  • Heterogeneous Mixtures: Have a non-uniform composition, like a salad or sand mixed with iron filings.

3.0Solutions

A solution is a homogeneous mixture of a solvent (major component) and a solute (minor component). Examples include lemonade and soda water.

Properties of a Solution:

  • Homogeneous mixture.
  • Particles are smaller than 1 nanometer and invisible to the naked eye.
  • Does not scatter light (Tyndall effect).
  • Stable and cannot be separated by filtration.

Types

Solute

Solvent

Example

Solid solutions

solid

solid

Brass, bronze. steel,

liquid

solid

dental amalgam,

gas

solid

hydrogen in palladium

Liquid solutions

solid

liquid

sugar in water, seawater

liquid

liquid

Vinegar, alcohol in water

gas

liquid

soft drinks

Gaseous solutions

solid

gas

naphthalene in air

liquid

gas

perfume in air

gas

gas

carbon monoxide in the air

Concentration of a Solution

It is the amount of solute in a given solution. Based on solute quantity, solutions can be dilute, concentrated, or saturated (when no more solute can dissolve at a given temperature). Concentration is commonly expressed in three ways:

Mass by Mass Percentage: Mass of solute per mass of solution.


Mass by Volume Percentage: This measures the solute's mass relative to the solution's volume.


Volume by Volume Percentage: Volume of solute per volume of solution.

4.0Suspensions

A suspension is a heterogeneous mixture in which solid particles are dispersed in a liquid but remain undissolved.

Properties of a Suspension:

  • Heterogeneous mixture.
  • Visible particles.
  • It scatters light, showing the Tyndall effect.
  • Particles settle over time.
  • It can be separated by filtration.

5.0Colloidal Solutions

A colloid is a heterogeneous mixture in which particles are uniformly distributed but not visible to the naked eye.

Dispersed Phase

Dispersion Medium

Type of colloid

Example

Solid

Solid

Solid-sol

Ruby glass, alloys

Solid

Liquid

Sol

paint, ink

Solid

Gas

Aerosol

Smoke, haze

Liquid

Solid

Gel

Curd, cheese

Liquid

Liquid

Emulsion

Milk, Cream

Liquid

Gas

Liquid Aerosol

Cloud, mist

Gas

Solid

Solid foam

Cork, pumice stone

Gas

Liquid

Foam

Froths of air

Properties of Colloidal Solutions:

  • Heterogeneous mixture.
  • Scatter light, making the Tyndall effect visible.
  • Particles do not settle out.
  • It cannot be separated by filtration but can be separated through centrifugation.

Components of a Colloid:

  • Dispersed Phase: The particles that are distributed within a mixture.
  • Dispersion Medium: The substance in which these particles are suspended.

The following table clearly compares the properties of true solutions, suspensions, and colloidal solutions:

Property

True Solutions

Suspension

Colloidal Solution

Particle Size

Less than 10⁻⁹ m / 1 nm

Greater than 10⁻⁶ m / 1000 nm

Between 10⁻⁹ to 10⁻⁶ m / 1 to 1000 nm

Visibility of Particles

Invisible to naked eye and under a powerful microscope

Easily visible

Invisible to naked eye; visible under a powerful microscope

Sedimentation of Particles

Do not settle down

Settle down due to gravity

Settle down under high centrifugation

Filtration through Filter Paper

No residue is formed

Residue is formed

No residue is formed

Mixture Type

Homogeneous

Heterogeneous

Heterogeneous

Appearance

Clear and Transparent

Translucent or Opaque

Translucent

6.0Physical and Chemical Changes

  • Physical Changes: Changes that affect the physical properties of matter without changing its chemical composition. Examples include changes in state (melting, boiling).
  • Chemical Changes  Result in the formation of new substances with different properties. Examples include iron rusting and combustion.

7.0Pure Substances: Elements and Compounds

Elements: Form of matter that cannot be broken down into simpler substances by chemical reactions. First defined by Antoine Lavoisier, elements are classified as:

  • Metals: Shiny, malleable, good conductors (e.g., gold, silver, copper).
  • Non-metals: Dull, brittle, poor conductors (e.g., oxygen, iodine).
  • Metalloids: Have properties of both metals and nonmetals (e.g., silicon, boron).

Compounds: Formed when two or more elements chemically combine in fixed proportions. The properties of compounds differ from their constituent elements, and their composition is uniform throughout.

8.0Differences Between Mixtures and Compounds

Mixtures

Compounds

Elements or compounds mix together without forming a new substance.

Elements react to form new substances.

A mixture has a variable composition.

The composition of a compound is always fixed.

A mixture retains the properties of its individual components.

The properties of a compound are different from those of its components.

Physical methods can separate components.

Components can only be separated by chemical or electrochemical reactions.

9.0Key Features of CBSE Class 9 Science Notes Chapter 2 – Is Matter Around Us Pure?

  • Complete Chapter Coverage: Covers all essential concepts including mixtures, solutions, types of mixtures, separation techniques, and pure substances.
  • Simplified Language: Complex scientific terms and definitions are explained in simple, student-friendly language for better understanding.
  • Based on Latest NCERT Curriculum: Fully aligned with the updated CBSE syllabus to ensure you study exactly what’s required for exams.
  • Well-Structured Layout: CBSE Notes are neatly organized with headings, subheadings, bullet points, diagrams, and flowcharts for easy navigation.
  • Illustrative Diagrams & Examples: Includes labeled diagrams, real-life examples, and concept illustrations to make learning more visual and relatable.

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