Science · Class 9 · Chapter 5

Exploring Mixtures and their Separation

• Homogeneous / Heterogeneous — Uniform throughout / not uniform composition.
• Concentration — Amount of solute in a given solvent or solution.
• Saturated solution — Cannot dissolve any more solute at that temperature.
• Crystallization — Growing pure crystals from a cooling saturated solution.
• Distillation — Separating miscible liquids by differing boiling points.
• Chromatography — Separating components by their rate of movement.
• Sublimation / Deposition — Solid ↔ vapour, without passing through liquid.
• Centrifugation / Coagulation — Spinning out heavy particles / clumping fine ones.
• Colloid — Mixture with particles too small to settle, but large enough to scatter light.
• Tyndall effect — Scattering of light by colloid or suspension particles.

Chapter 5 · Concept 1 of 18

Homogeneous and Heterogeneous Mixtures

• Homogeneous mixture — Uniform composition throughout — the first sip tastes exactly like the last. Also called a solution. Example: sugar in water, vinegar, soda.
• Heterogeneous mixture — Not uniform — components stay visibly distinct and may settle over time. Example: sand in water, oil in water.

Chapter 5 · Concept 2 of 18

Solute, Solvent, and Concentration

• A solute (the substance dissolved) mixes into a solvent (the substance that dissolves it) to form a solution.
• Proportion matters — Oral Rehydration Solution (ORS) only works if the salt and sugar are in the right proportion with water — too little or too much changes the outcome, just as too much pesticide can damage a crop.

Chapter 5 · Concept 3 of 18

% m/m — Grams of Solute per 100 g Solution

• Formula — % m/m = (Mass of solute ÷ Mass of solution) × 100 Used for both homogeneous and heterogeneous mixtures — e.g. milk powder, spice mixes, and food labels.
• Worked example — 10 g salt dissolved in 90 g water. Total solution mass = 10 + 90 = 100 g. % m/m = (10 ÷ 100) × 100 = 10% m/m.

Chapter 5 · Concept 4 of 18

% m/v — Grams of Solute per 100 mL Solution

• Formula — % m/v = (Mass of solute ÷ Volume of solution) × 100 Used where measuring volume is easier than weighing — common in medicines, like a 5% glucose solution or 0.9% saline.
• Worked example — 5 g glucose dissolved to make 100 mL of solution. % m/v = (5 ÷ 100) × 100 = 5% m/v.

Chapter 5 · Concept 5 of 18

% v/v — mL of Solute per 100 mL Solution

• Formula — % v/v = (Volume of solute ÷ Volume of solution) × 100 Used when two miscible liquids mix — e.g. perfumes, cosmetics, and vinegar (5% v/v acetic acid).
• Worked example — 1 mL pesticide mixed with water to make 100 mL spray. % v/v = (1 ÷ 100) × 100 = 1% v/v.

Chapter 5 · Concept 6 of 18

Solubility and Solubility Curves

• Solubility = the maximum solute that dissolves in a fixed amount of solvent, at a given temperature. Beyond that, the solution is saturated.
• Solid vs gas solutes — A solid's solubility usually rises with temperature, but a gas's solubility usually falls as it gets warmer.

Chapter 5 · Concept 7 of 18

Crystallization

• Cool a hot, saturated solution slowly — the solute that no longer fits comes out of solution as pure, regularly-shaped crystals.
• Purifies as it separates — Based on the fact that solubility changes with temperature. Used to separate two soluble solids (one in small quantity), and to purify solids — like copper sulfate crystals grown from a filtered, cooled solution.

Chapter 5 · Concept 8 of 18

Distillation

• Heat a mixture of miscible liquids until the lower-boiling-point liquid vaporises, then cool the vapour back into a pure liquid.
• Heat the mixture
• Lower-bp liquid vaporises
• Vapour cools in the condenser
• Pure liquid collected

Chapter 5 · Concept 9 of 18

Fractional Distillation

• Small boiling-point gaps — Used when components' boiling points differ by less than 25 °C — the mixture is separated into fractions instead of one clean cut.
• Refining crude oil — A petroleum refinery uses fractional distillation to split crude oil into petroleum gas, petrol, kerosene, diesel, lubricating oil, and bitumen.

Chapter 5 · Concept 10 of 18

Paper Chromatography

• A solvent rises up a paper strip, carrying dissolved components with it — different substances travel at different speeds.
• Separates by speed of movement — As the solvent rises through paper, ink or plant pigments separate into distinct colour spots, based on how each component interacts with the paper and the solvent.

Chapter 5 · Concept 11 of 18

The Separating Funnel

• Oil and water don't mix — they settle into two distinct layers, by density.
• Denser liquid drains first — In a separating funnel, mustard oil floats above water. Opening the stopcock drains the denser water out first; closing it in time keeps the oil layer separate above.

Chapter 5 · Concept 12 of 18

Sublimation

• Sublimation — A solid changes directly into vapour, without melting into a liquid first — like camphor or naphthalene separating from sand on gentle heating.
• Deposition — The reverse: vapour cools and turns directly back into a solid, without becoming liquid — the camphor deposits form on a cool funnel wall.

Chapter 5 · Concept 13 of 18

Alloys

• Metals melted together and cooled solidify into a new, uniform material — an alloy. Physical methods cannot separate its components.
• Alloy | Composition
• Brass — ~80% copper, 20% zinc
• Bronze — ~80% copper, 20% tin
• Stainless steel — Iron with carbon, chromium, nickel, molybdenum

Chapter 5 · Concept 14 of 18

Suspensions

• Solid particles that don't dissolve, but stay suspended throughout a liquid, and are visible to the naked eye.
• Filtration isn't always enough — Muddy water filtered through cloth may still look cloudy — the finest particles pass right through, needing centrifugation or coagulation instead.

Chapter 5 · Concept 15 of 18

Centrifugation

• Spinning a mixture at high speed throws heavier particles outward and downward, while the lighter liquid stays on top.
• Blood, spun apart — Centrifugation separates blood into plasma, platelets, white blood cells, and red blood cells — and works even in a hand-powered "paperfuge" with no electricity.

Chapter 5 · Concept 16 of 18

Coagulation

• A coagulant makes fine suspended particles clump into larger masses, which then settle by gravity.
• From muddy water to paneer — Alum (fitkari) coagulates impurities in muddy water for purification; lemon juice or vinegar coagulates milk proteins to make paneer.

Chapter 5 · Concept 17 of 18

Solution, Colloid, or Suspension?

• | Solution | Colloid | Suspension
• Particle size — < 1 nm — 1 – 1000 nm — > 1000 nm
• Visible to the eye — No — No — Yes
• Settles over time — No — No — Yes
• Separated by filtration — No — No — Yes
• Example — Salt solution — Milk, blood — Sand in water

Chapter 5 · Concept 18 of 18

The Tyndall Effect

• Scattering of light — Colloid and suspension particles scatter light, making a light beam's path visible — as with sunlight through dust, or floodlights in a stadium. A true solution shows no such path.
• Emulsions — A colloid where both the dispersed phase and medium are liquids. Milk is oil-in-water; butter is water-in-oil — stabilised by emulsifying agents like milk proteins.

Quick Recap

Check Your Understanding

1. 1Which of the following mixtures are correctly classified as homogeneous (Hm) and heterogeneous (Ht)?
2. 2Which among the following mixtures show the Tyndall Effect? (a) air and dust particles (b) copper sulfate and water (c) starch and water (d) acetone and water
3. 3Complete the table with the correct properties and examples for each type of mixture.