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Is Matter Around Us Pure?

CBSE Class 9 Science • Chapter 2 • Detailed Master Notes

Chapter Overview:

Matter is classified into Pure Substances and Mixtures. This chapter explores Elements, Compounds, Mixtures (Homogeneous and Heterogeneous), Solutions, Suspension, Colloids, and various Techniques of Separation which are crucial for understanding purification processes.

1. Classification of Matter

Matter is classified based on its chemical composition.

Pure Substance: Consists of a single type of particles.
- Elements: Basic form of matter that cannot be broken down into simpler substances by chemical reactions. (e.g., Iron, Oxygen, Gold).
  Types: Metals (Conductors, Malleable), Non-Metals (Insulators, Brittle), Metalloids (Intermediate properties).
- Compounds: Two or more elements chemically combined in a fixed proportion by mass. (e.g., Water $H_2O$, Salt $NaCl$).
Mixture: Constituted by more than one form of matter (substance) mixed in any proportion. (e.g., Air, Lemonade, Soil).

Mixtures vs Compounds

Mixture (e.g., Iron powder + Sulphur powder)	Compound (e.g., Iron Sulphide - $FeS$)
Elements or compounds just mix together. No new substance formed.	Elements react to form new substances.
Variable composition.	Fixed composition.
Shows properties of constituent substances. (Iron attracts magnet).	New substance has totally different properties. (Not attracted by magnet).
Constituents can be separated easily by physical methods.	Constituents separated only by chemical/electrochemical reactions.

2. Types of Mixtures

Homogeneous Mixture	Heterogeneous Mixture
Uniform composition throughout.	Non-uniform composition.
No visible boundaries of separation.	Visible boundaries of separation.
e.g., Sugar in water, Alloys, Air.	e.g., Sand and salt, Oil and water.

3. Solution, Suspension, and Colloid

(a) Solution

A homogeneous mixture of two or more substances. Components: Solute (dissolved) + Solvent (dissolving medium). (e.g., Tincture of Iodine: Iodine is solute, Alcohol is solvent).

Properties:

Particles are very small ($< 1 nm$) and cannot be seen by naked eye.
They do not scatter a beam of light (No Tyndall effect). Path of light is not visible.
Stable: Solute particles do not settle down when left undisturbed.
Solute particles cannot be separated by filtration.

(i) Concentration of Solution: Amount of solute present in a given amount of solution.

$$ \text{Mass by Mass \%} = \frac{\text{Mass of Solute}}{\text{Mass of
                Solution}} \times 100 $$

$$ \text{Mass by Volume \%} = \frac{\text{Mass of Solute}}{\text{Volume of
                Solution}} \times 100 $$

(ii) Saturated Solution: A solution in which no more solute can be dissolved at that temperature.

(iii) Solubility: The amount of solute present in saturated solution at a specific temperature.

(b) Suspension

A heterogeneous mixture containing solid particles big enough for sedimentation.

Particles are large ($> 100 nm$) and visible to naked eye.
Scatter a beam of light (Tyndall effect). Path of light is visible.
Unstable: Particles settle down when left undisturbed.
Can be separated by filtration. e.g., Chalk powder in water, Muddy water.

(c) Colloid (Colloidal Solution)

Heterogeneous mixture where particle size is intermediate between solution and suspension. Looks homogeneous but is actually heterogeneous.

Particles are too small to be seen (~1-100 nm).
Tyndall Effect: Scattering of a beam of light by colloidal particles is observed.
Stable: Particles do not settle. e.g., Milk, Fog, Cloud.
Cannot be separated by filtration (Centrifugation is used).

[IMAGE: TYNDALL EFFECT]

AI Prompt: "Scientific logic diagram: 'Tyndall Effect'. Two beakers side-by-side. 1. True Solution (Clear blue liquid): Torch light passes through INVISIBLY (No scattering). 2. Functional Colloid (Milk/Cloudy liquid): Torch light beam is VISIBLE inside the liquid (Scattering). Label: Solute < 1nm vs Colloid 1-100nm."

Classification of Colloids (Dispersed Phase + Dispersing Medium)

[IMAGE: COLLOIDS TABLE]

AI Prompt: "A colorful infographic table: 'Types of Colloids'. Columns: Dispersed Phase, Dispersing Medium, Type, Example. Rows: 1. Liquid in Gas (Aerosol - Fog/Cloud). 2. Solid in Gas (Aerosol - Smoke). 3. Gas in Liquid (Foam - Shaving Cream). 4. Liquid in Liquid (Emulsion - Milk). 5. Solid in Liquid (Sol - Mud)."

4. Separation Techniques (Detailed)

Heterogeneous mixtures can be separated by simple physical methods (picking, sieving). Special techniques are needed for others.

1. Evaporation

Principle: Separate volatile component (Solvent like water) from non-volatile component (Solute like dye) by heating.
Application: Obtaining colored component (dye) from blue/black ink.

2. Centrifugation

Principle: Denser particles are forced to the bottom and lighter particles stay at the top when spun rapidly.
Application: Separating Cream from Milk, Blood/Urine tests in labs, Washing machines (squeeze out water).

3. Separating Funnel

Principle: Immiscible liquids separate out in layers depending on their densities.
Application: To separate mixture of Oil and Water (Oil floats on water). Extraction of Iron from ore.

[IMAGE: SEPARATING FUNNEL]

AI Prompt: "Diagram of 'Separating Funnel'. A glass funnel with a stopcock at the bottom. Two distinct liquid layers. Top layer: Yellow (Kerosene/Oil). Bottom layer: Blue (Water). Beaker below collecting water. Labels: 'Lighter Liquid', 'Heavier Liquid', 'Stopcock'."

4. Sublimation

Principle: To separate mixtures having a sublimable volatile component from a non-sublimable impurity on heating.
Application: Ammonium Chloride + Salt. Camphor, Naphthalene, Anthracene.

[IMAGE: SUBLIMATION DIAGRAM]

AI Prompt: "Same as Chapter 1 Sublimation diagram but distinct. Focus on separating 'Mixture of Salt and Ammonium Chloride'. Inverted funnel, cotton plug, burner. Vapours solidifying on cool walls. Salt remains in the china dish."

5. Chromatography

Principle: Separation of those solutes that dissolve in the same solvent. The component that is more soluble rises faster on filter paper.
Application: Separate colours in a dye, Pigments from natural colours (flowers), Drugs from blood.

6. Distillation

Principle: Separation of two miscible liquids that boil without decomposition and have sufficient difference in boiling points ($>25 K$).
Application: Acetone and Water.

[IMAGE: DISTILLATION APPARATUS]

AI Prompt: "Laboratory setup for 'Distillation'. Distillation flask with thermometer containing Acetone+Water mixture. Heated by burner. Side tube connected to a Liebig Condenser (water cooling). Liquid Acetone collecting in a beaker. Water remains in flask."

7. Fractional Distillation

Principle: For miscible liquids with boiling point difference $< 25 K$. A fractionating column (packed with glass beads) is used to provide surface for vapours to cool and condense repeatedly.
Application: Separation of different gases from Air, Crude Oil refining (Petrol, Diesel).

[IMAGE: FRACTIONAL DISTILLATION]

AI Prompt: "Schematic of 'Separation of Components of Air'. Flowchart style. 1. Air (Compressed & Cooled) -> Liquid Air. 2. Allowed to warm up in Fractional Distillation Column. 3. Gases separate at heights: Nitrogen (-196°C) Top, Argon (-186°C) Middle, Oxygen (-183°C) Bottom."

8. Crystallisation

Principle: Process that separates a pure solid in the form of its crystals from a solution. Better than evaporation as some solids decompose (sugar) or impurities remain on evaporation.
Application: Purification of Salt from sea water, Separation of crystals of Alum (phitkari) from impure samples.

5. Purification of Water (Water Works)

[IMAGE: WATER PURIFICATION SYSTEM]

AI Prompt: "Schematic Diagram of 'Water Purification System'. 1. Reservoir. -> 2. Sedimentation Tank (Solids settle). -> 3. Loading Tank (Suspended impurities settle). -> 4. Filtration Tank (Sand/Gravel layers). -> 5. Chlorination Tank (Kill bacteria) -> 6. To Home Tap."

6. Physical and Chemical Changes

Physical Change: No new substance formed. Reversible. Only properties like state, shape, color change. (e.g., Melting of ice, Cutting of trees, Boiling water).
Chemical Change: New substance with different chemical properties is formed. Irreversible. (e.g., Burning of paper, Rusting of iron, Cooking food, Growth of plant).

Practice Zone

Q1: Which separation technique will you apply for the separation of Sodium Chloride from its solution in water?

Ans: Evaporation.

Q2: Classify as Physical or Chemical change: (a) Rusting of almirah (b) Dissolving salt in water.

Ans: (a) Chemical Change. (b) Physical Change.