How are sweet, white crystals of sugar obtained from tall, green sugarcane — and how do doctors detect malaria using just a few drops of blood?
Key idea
Homogeneous and Heterogeneous Mixtures
1
Homogeneous mixture
Uniform composition throughout — the first sip tastes exactly like the last. Also called a solution. Example: sugar in water, vinegar, soda.
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Heterogeneous mixture
Not uniform — components stay visibly distinct and may settle over time. Example: sand in water, oil in water.
Key idea
Solute, Solvent, and Concentration
A solute (the substance dissolved) mixes into a solvent (the substance that dissolves it) to form a solution.
Proportion mattersOral 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.
Key idea
% m/m — Grams of Solute per 100 g Solution
1
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.
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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.
Key idea
% m/v — Grams of Solute per 100 mL Solution
1
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.
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Worked example
5 g glucose dissolved to make 100 mL of solution. % m/v = (5 ÷ 100) × 100 = 5% m/v.
Key idea
% v/v — mL of Solute per 100 mL Solution
1
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).
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Worked example
1 mL pesticide mixed with water to make 100 mL spray. % v/v = (1 ÷ 100) × 100 = 1% v/v.
Key idea
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 solutesA solid's solubility usually rises with temperature, but a gas's solubility usually falls as it gets warmer.
Key idea
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.
Key idea
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
Key idea
Fractional Distillation
1
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.
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Refining crude oil
A petroleum refinery uses fractional distillation to split crude oil into petroleum gas, petrol, kerosene, diesel, lubricating oil, and bitumen.
Key idea
Paper Chromatography
A solvent rises up a paper strip, carrying dissolved components with it — different substances travel at different speeds.
Separates by speed of movementAs 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.
Key idea
The Separating Funnel
1
Oil and water don't mix
they settle into two distinct layers, by density.
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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.
Key idea
Sublimation
1
Sublimation
A solid changes directly into vapour, without melting into a liquid first — like camphor or naphthalene separating from sand on gentle heating.
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Deposition
The reverse: vapour cools and turns directly back into a solid, without becoming liquid — the camphor deposits form on a cool funnel wall.
Key idea
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
Key idea
Suspensions
Solid particles that don't dissolve, but stay suspended throughout a liquid, and are visible to the naked eye.
Filtration isn't always enoughMuddy water filtered through cloth may still look cloudy — the finest particles pass right through, needing centrifugation or coagulation instead.
Key idea
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.
Key idea
Coagulation
A coagulant makes fine suspended particles clump into larger masses, which then settle by gravity.
From muddy water to paneerAlum (fitkari) coagulates impurities in muddy water for purification; lemon juice or vinegar coagulates milk proteins to make paneer.
Key idea
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
Key idea
The Tyndall Effect
1
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.
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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.
Chapter · Key terms to remember
Key Terms
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.
Chapter · Key terms to remember
More Key Terms
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.
Chapter · Key terms to remember
More Key Terms
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.
Chapter · Key terms to remember
More Key Terms
Tyndall effect
Scattering of light by colloid or suspension particles.
Questions for your notebook
Write these down, then discuss
1
Which of the following mixtures are correctly classified as homogeneous (Hm) and heterogeneous (Ht)?
2
Which 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
Complete the table with the correct properties and examples for each type of mixture.
Project as-is — students copy the questions, then the class discusses answers together.