Class 9 Science Chapter 5 – Exploring Mixtures and Their Separation

Chapter 5: Exploring Mixtures and Their Separation

Introduction:
Mixtures are combinations of two or more substances. Separation of mixtures is important in daily life, industries, and medical fields such as sugar production and blood testing.

5.1 Classification of Mixtures

Homogeneous Mixture: Uniform composition throughout.
Examples: Sugar solution, vinegar, soda.

Heterogeneous Mixture: Non-uniform composition.
Examples: Sand + water, oil + water.

Key Activity (Laser Test)

• Salt + water → No visible particles → Solution
• Chalk + water → Particles visible → Suspension
• Milk + water → Appears uniform but scatters light → Colloid

5.2 Solutions

Solution: Homogeneous mixture of solute and solvent.
• Solute → Substance dissolved
• Solvent → Substance that dissolves solute

5.2.1 Concentration of Solution

Concentration = Amount of solute in a given amount of solvent/solution.

5.2.2 Methods to Express Concentration

1. Mass by Mass (% m/m)

Formula:
% m/m = (Mass of solute / Mass of solution) × 100

Example:
10g salt + 90g water = 100g solution
% m/m = (10/100) × 100 = 10%

2. Mass by Volume (% m/v)

Formula:
% m/v = (Mass of solute / Volume of solution) × 100

Example:
5g glucose in 100 mL → 5%

3. Volume by Volume (% v/v)

Formula:
% v/v = (Volume of solute / Volume of solution) × 100

Example:
1 mL pesticide in 100 mL → 1%

5.2.3 Solubility

Solubility = Maximum solute dissolved in 100g/100mL solvent at a given temperature.

• Increases with temperature (solids)
• Decreases with temperature (gases)

Saturated Solution: Cannot dissolve more solute.

5.3 Separation of Homogeneous Mixtures

1. Crystallization

Formation of pure crystals from saturated solution.

Principle: Solubility changes with temperature.

Steps:
• Prepare saturated solution
• Filter impurities
• Cool slowly → crystals form

2. Distillation

Used to separate miscible liquids based on boiling points.

Principle:
Lower boiling liquid vaporises first → condenses → collected.

Example:
Acetone (56°C) + Water (100°C)

Fractional Distillation

Used when boiling point difference is small (<25°C).
Example: Petroleum refining

3. Paper Chromatography

Separates substances based on movement rate on paper.

Principle:
Different substances move at different speeds.

5.4 Separation of Heterogeneous Mixtures

1. Separating Funnel

Used for immiscible liquids (oil + water).
Based on density difference.

2. Sublimation

Solid → Vapour (without liquid stage)

Examples:
Camphor, naphthalene, dry ice

3. Suspensions

• Heterogeneous
• Particles visible
• Settle on standing
Example: Muddy water

4. Centrifugation

Spinning separates heavier particles.

Example:
Blood separation

5. Coagulation

Small particles combine into larger ones.

Example:
Alum purifies water

5.4.4 Colloids

• Intermediate particle size (1–1000 nm)
• Do not settle
• Show Tyndall effect

Examples:
Milk, blood, ice cream

5.5 Tyndall Effect

Scattering of light by particles.

Observed in:
• Fog
• Smoke
• Sunlight through trees

Comparison Table

Property	Solution	Suspension	Colloid
Nature	Homogeneous	Heterogeneous	Heterogeneous (appears uniform)
Particle Size	< 1 nm	> 1000 nm	1–1000 nm
Visibility	Not visible	Visible	Not visible
Settling	No	Yes	No
Tyndall Effect	No	Yes	Yes

Important Points

• Mixtures can be homogeneous or heterogeneous.
• Crystallization purifies solids.
• Distillation separates liquids.
• Chromatography separates colours.
• Sublimation separates special solids.
• Centrifugation separates heavy particles.
• Tyndall effect distinguishes colloids.