📘 Class 9 Science ( Chapter: Is Matter Around Us Pure? )
🔹 Introduction
In daily life, we call materials like milk and water “pure”.
Scientific meaning of pure: A material made up of only one kind of particle (atoms or molecules).
Most substances around us are not pure, but mixtures of different substances.
🔹 Types of Matter
| Type | Composition | Example |
|---|---|---|
| Pure Substance | Made of a single type of particle | Distilled water, oxygen gas |
| Mixture | Contains two or more different substances | Air, sugar solution, alloys |
🔹 Pure Substances
Definition: A substance that has a fixed composition and cannot be separated by physical methods.
🔿 Elements
Made of same type of atoms.
Cannot be broken down further by chemical means.
Types: Metals, Non-metals, Metalloids.
| Category | Properties | Examples |
|---|---|---|
| Metals | Malleable, ductile, good conductor | Iron, Copper |
| Non-metals | Brittle, poor conductors, dull | Sulphur, Oxygen |
| Metalloids | Properties of both metals and non-metals | Silicon |
🔿 Compounds
Formed by chemical combination of two or more elements in fixed ratio.
Properties of compound are different from the elements.
Can only be separated by chemical methods.
| Compound | Elements Involved | Formula |
|---|---|---|
| Water | Hydrogen and Oxygen | Hâ‚‚O |
| Carbon dioxide | Carbon and Oxygen | COâ‚‚ |
| Sodium chloride | Sodium and Chlorine | NaCl |
🔹 Mixtures
Definition: Combination of two or more substances not chemically combined.
Can be separated using physical methods.
🔿 Types of Mixtures
| Type | Description | Examples |
|---|---|---|
| Homogeneous | Uniform composition throughout | Air, vinegar, salt water |
| Heterogeneous | Non-uniform composition | Oil in water, sand in iron |
🔹 Solutions (Homogeneous Mixtures)
Definition: A uniform mixture formed when solute dissolves in solvent.
🔿 Components
Solute: The substance that is dissolved.
Solvent: The substance that dissolves the solute.
🔿 Characteristics
Clear and transparent.
Particle size < 1 nm.
Stable (no settling).
No Tyndall effect.
🔿 Types of Solutions
| Type | Solute in Solvent | Example |
|---|---|---|
| Solid in solid | Metal in metal | Brass (zinc in copper) |
| Solid in liquid | Sugar in water | Sugar solution |
| Gas in liquid | COâ‚‚ in water | Soda |
| Gas in gas | Various gases in air | Air |
🔹 Concentration of Solution
Definition: The amount of solute present in a given quantity of solution.
| Term | Meaning |
|---|---|
| Dilute solution | Small amount of solute |
| Concentrated solution | Large amount of solute |
Formula:
Concentration=Mass of solute / Mass of solution ×100
🔹 Suspension (Heterogeneous Mixture)
Mixture where large particles are visible and settle down.
Example: Mud in water, chalk in water.
🔿 Characteristics
Particles are visible.
Heterogeneous and unstable.
Can be separated by filtration.
Shows Tyndall effect.
🔹 Colloids (Heterogeneous but Stable Mixture)
Particles are not truly dissolved but don’t settle either.
Examples: Milk, smoke, mist, foam.
🔿 Properties
Appears homogeneous to naked eye.
Particle size between 1-1000 nm.
Particles do not settle.
Cannot be filtered easily.
Tyndall effect present.
🔿 Components
| Component | Description |
|---|---|
| Dispersed phase | The particles distributed |
| Dispersion medium | The medium in which they are spread |
🔿 Types of Colloids
| Type | Dispersed Phase | Dispersion Medium | Example |
|---|---|---|---|
| Foam | Gas | Liquid | Shaving cream |
| Emulsion | Liquid | Liquid | Milk, mayonnaise |
| Aerosol | Solid/Liquid | Gas | Smoke, fog |
| Sol | Solid | Liquid | Paint, muddy water |
| Gel | Liquid | Solid | Jelly, cheese |
🔹 Tyndall Effect
Phenomenon where light is scattered by particles in a colloid or suspension.
Not seen in true solutions.
Examples:
Light beam visible through fog or dusty room.
Sunlight passing through trees on a foggy morning.
🔹 Separation of Mixture Components
Mixtures can be separated by physical methods based on physical properties like size, boiling point, solubility, etc.
| Method | Principle Used | Example |
|---|---|---|
| Handpicking | Size and appearance | Removing stones from rice |
| Filtration | Solubility and particle size | Separating sand from water |
| Evaporation | Different boiling points | Getting salt from seawater |
| Sublimation | Sublimable substances | Separating camphor from salt |
| Distillation | Difference in boiling point | Separating alcohol and water |
| Fractional Distillation | Closer boiling points | Separating components of petroleum |
| Chromatography | Difference in solubility | Separating colors in ink |
| Centrifugation | Density difference | Separating cream from milk |
| Decantation | Heavier particles settle | Sand and water |
| Crystallisation | Solubility differences | Purifying sugar from solution |
🗌 Key Points to Remember
Pure substances contain only one kind of particle.
Mixtures can be homogeneous or heterogeneous.
Colloids show Tyndall effect and are stable.
Separation techniques depend on physical properties of components.