Exploring Mixtures and Their Separation
Complete chapter notes with a visual mind map, definitions, formulae, principle-based separation charts, activity capsules, sticky-note revision and exam-ready question answers.
Chapter Mind Map
The entire chapter on one visual study canvas.
Two or more substances physically combined in any proportion
🔎 Classification
- Homogeneous: uniform composition
- Heterogeneous: non-uniform composition
- Solution, colloid and suspension
💧 Solutions
- Solute + solvent
- Concentration: % m/m, % m/V, % V/V
- Saturated and unsaturated solutions
- Solubility and temperature
⚗ Homogeneous Separation
- Evaporation
- Crystallisation
- Simple/fractional distillation
- Paper chromatography
🧪 Heterogeneous Separation
- Separating funnel
- Sublimation
- Sedimentation, decantation, filtration
- Centrifugation and coagulation
🌫 Colloids
- Dispersed phase + dispersion medium
- Emulsions and emulsifying agents
- Tyndall effect
🏭 Applications
- Salt and crystal production
- Blood separation and paperfuge
- Water purification
- Perfumes, alloys and dairy products
Mixture Basics
Start with the key idea: components keep their identities because no new substance is formed.
Variable composition
The proportion of components can change. Lemonade may contain more or less sugar.
Properties retained
Each component generally keeps its characteristic properties. Iron remains magnetic in iron–sulphur mixture.
Physical separation
Differences in size, density, solubility, boiling point or other physical properties are used.
Classification by uniformity
| Feature | Homogeneous mixture | Heterogeneous mixture |
|---|---|---|
| Composition | Uniform throughout | Non-uniform; different regions may differ |
| Phases seen | Appears as a single phase | Often has two or more distinguishable phases |
| Components | Not separately visible | May be visible directly or under a microscope |
| Examples | Air, salt solution, vinegar, brass | Muddy water, oil and water, smoke, milk |
| Important note | A true solution is homogeneous | Suspensions and colloids are heterogeneous, though colloids may look uniform |
Pure substance vs mixture
Pure substance: one kind of particle and fixed composition; e.g., pure copper or distilled water.
Mixture: two or more kinds of particles and variable composition; e.g., air or seawater.
Miscible vs immiscible liquids
Miscible: liquids that mix completely, e.g., acetone and water.
Immiscible: liquids that do not mix and form layers, e.g., oil and water.
Solutions and Concentration
Three formulae form the numerical core of the chapter.
Solute
The component that gets dissolved, usually present in the smaller amount.
Sugar in sugar solutionSolvent
The component that dissolves the solute, usually present in the larger amount.
Water in sugar solutionSolution
The uniform mixture formed when the solute disperses at particle level in the solvent.
Solute + solventSolutions can exist in different states
| Solute | Solvent | Example | Type |
|---|---|---|---|
| Gas | Gas | Air | Gas solution |
| Gas | Liquid | Carbon dioxide in soda water | Gas in liquid |
| Liquid | Liquid | Acetic acid in water (vinegar) | Liquid in liquid |
| Solid | Liquid | Salt in water | Solid in liquid |
| Solid | Solid | Zinc in copper (brass) | Solid solution/alloy |
| Expression | Formula | Use it when | Meaning |
|---|---|---|---|
| Mass by mass % m/m | (Mass of solute ÷ Mass of solution) × 100 | Masses are given in grams | Grams of solute per 100 g solution |
| Mass by volume % m/V | (Mass of solute ÷ Volume of solution) × 100 | Solute mass and solution volume are given | Grams of solute per 100 mL solution |
| Volume by volume % V/V | (Volume of solute ÷ Volume of solution) × 100 | Both solute and solution are liquids | Millilitres of solute per 100 mL solution |
1. % m/m
% m/m = mass of solutemass of solution × 100Example: 10 g salt + 90 g water.
Mass of solution = 10 + 90 = 100 g
% m/m = (10 ÷ 100) × 100 = 10%
2. % m/V
% m/V = mass of solutevolume of solution × 100Example: 5 g glucose in 100 mL solution.
% m/V = (5 ÷ 100) × 100 = 5%
3. % V/V
% V/V = volume of solutevolume of solution × 100Example: 30 mL concentrate in 150 mL drink.
% V/V = (30 ÷ 150) × 100 = 20%
Science and society: ORS
Correct concentration can be life-saving. Indian paediatrician Dr Dilip Mahalanabis pioneered the large-scale use of Oral Rehydration Solution during disease outbreaks. A correctly prepared ORS contains solutes in the right proportion to replace water and salts lost from the body.
Solubility, Saturation and Temperature
Solubility tells us the maximum—not just the actual—amount that can dissolve.
Solubility
Maximum amount of solute that dissolves in a fixed quantity of solvent at a specified temperature.
Unsaturated solution
A solution that can still dissolve more solute at the given temperature.
Saturated solution
A solution that cannot dissolve any more solute at the given temperature.
Effect of temperature
| System | General effect of raising temperature | Everyday connection |
|---|---|---|
| Most solids in liquids | Solubility usually increases | More sugar dissolves in hot water than in cold water |
| Gases in liquids | Solubility usually decreases | A warm soft drink loses dissolved carbon dioxide more easily |
Separation Techniques: Method + Principle
Choose a method only after identifying the physical property that differs.
The separation rule
Mixture → identify components → find a differing physical property → choose the matching technique.
particle sizedensitysolubilityboiling pointsublimabilitymagnetismaffinity for paper/solventMaster principle chart
| Technique | Type of mixture | Principle/property used | Example | Main result |
|---|---|---|---|---|
| Handpicking | Solid + solid | Visible difference in size, shape or colour | Stones from rice | Selected impurity removed |
| Sieving | Solid + solid | Difference in particle size | Bran from flour | Fine particles pass; coarse remain |
| Winnowing | Solid + solid | Difference in weight/density; moving air | Husk from grain | Lighter part blows away |
| Magnetic separation | Solid + solid | Difference in magnetic property | Iron filings from sand | Magnetic component attracted |
| Sedimentation | Insoluble solid + liquid | Heavier particles settle under gravity | Mud from muddy water | Sediment forms below |
| Decantation | Solid + liquid / immiscible liquids | Difference in density after settling/layering | Clear water above settled mud | Upper liquid poured off |
| Filtration | Insoluble solid + liquid | Particle size and porous barrier | Tea leaves from tea | Residue + filtrate |
| Evaporation | Soluble solid + liquid | Solvent is volatile; solute is non-volatile | Salt from seawater | Solid remains; solvent is lost |
| Crystallisation | Impure solid in solution | Solubility changes with temperature | Pure copper sulphate crystals | Pure crystals obtained |
| Simple distillation | Miscible liquids / solution | Large difference in boiling points, usually ≥ 25°C | Acetone + water | Lower-boiling liquid recovered |
| Fractional distillation | Miscible liquids | Small difference in boiling points | Fractions of crude oil | Liquids collected in fractions |
| Paper chromatography | Soluble coloured components | Different affinities for mobile solvent and stationary paper | Pigments in ink | Separate coloured spots |
| Separating funnel | Immiscible liquids | Difference in density and layer formation | Oil + water | Denser lower layer drained first |
| Sublimation | Solid + solid | One solid sublimes; the other does not | Camphor + sand | Sublimable solid deposited separately |
| Centrifugation | Fine solid/liquid or liquid/liquid dispersion | Difference in density under rapid spinning | Plasma from blood; cream from milk | Denser component moves outward/settles |
| Coagulation | Very fine suspension/colloid | Small particles clump into larger flocs | Alum in muddy water | Flocs settle and can be filtered |
Evaporation
Principle: difference in volatilityThe solvent changes into vapour from the surface, while a non-volatile dissolved solid remains. It can occur at any temperature, though heating makes it faster.
Best when: only the dissolved solid is needed and the solvent need not be recovered.
Crystallisation
Principle: change in solubility with temperatureA hot saturated solution is cooled slowly so excess solute forms pure, well-shaped crystals. Impurities remain in the mother liquor or are removed by filtration.
Why better than evaporation for purification? It gives purer crystals, leaves soluble impurities in the mother liquor and avoids heating a solid to complete dryness.
Simple Distillation
Principle: sufficiently different boiling pointsThe lower-boiling liquid vaporises first. Its vapour passes through a condenser, cools and changes back into liquid called the distillate.
Use: acetone (56°C) + water (100°C); or recovering water from salt solution. Use fractional distillation when miscible liquids have close boiling points.
Paper Chromatography
Principle: different distribution/affinity between paper and solventPaper acts as the stationary phase and the rising solvent acts as the mobile phase. Components move at different speeds because their solubility in the solvent and attraction to paper differ.
Uses: separating dyes in ink, pigments in flowers or leaves and comparing unknown colour mixtures.
Separating Funnel
Principle: immiscibility + density differenceTwo immiscible liquids form separate layers. The denser liquid settles at the bottom and is drained first through the stopcock.
Sublimation
Principle: one solid changes directly into vapourA sublimable solid changes directly from solid to vapour on heating and deposits back as solid on a cool surface. The non-sublimable component remains behind.
Examples of sublimable solids: camphor, naphthalene, iodine and dry ice. Separation example: camphor from sand.
Centrifugation
Principle: density difference under rapid rotationRapid spinning increases the effective settling of denser particles or droplets. Denser components move farther outward and collect separately from the lighter medium.
Uses: separating blood cells from plasma, cream from milk and fine suspended solids in laboratories and industries.
Paperfuge
A low-cost, hand-powered paper centrifuge can spin small blood samples without electricity. It can support tests for conditions such as malaria and anaemia in remote areas.
Coagulation
Principle: fine particles aggregate into larger flocsA coagulant neutralises or reduces the repulsion between tiny particles, causing them to form larger clumps called flocs. The flocs settle and can then be removed by decantation or filtration.
Examples: alum (fitkari) in muddy water; acid causing milk proteins to coagulate during paneer making.
Evaporation vs crystallisation vs distillation
| Method | What happens? | What is collected? | Choose it when… |
|---|---|---|---|
| Evaporation | Solvent escapes from surface | Solid solute | Solvent is not required |
| Crystallisation | Hot saturated solution is cooled | Pure solid crystals | Pure, well-formed solid is required |
| Distillation | Liquid boils, vapour is condensed | Pure liquid/distillate | Solvent or lower-boiling liquid must be recovered |
India’s scientific heritage
Coastal communities have long obtained salt through evaporation and crystallisation. Kannauj’s traditional Deg–Bhapka distillation system is used to prepare attars, including the earthy fragrance known as Mitti ka Ittar.
Solution, Colloid and Suspension
Particle size explains settling, filtration and the Tyndall effect.
| Property | True solution | Colloid | Suspension |
|---|---|---|---|
| Nature | Homogeneous | Heterogeneous but appears uniform | Heterogeneous |
| Particle size | Less than 1 nm | 1–1000 nm | More than 1000 nm |
| Visibility | Not visible | Not visible to naked eye | Often visible to naked eye |
| Settling on standing | No | No | Yes |
| Ordinary filtration | Not separated | Not separated by ordinary filter paper | Usually separated |
| Tyndall effect | No | Yes | Yes |
| Examples | Salt solution, copper sulphate solution | Milk, fog, smoke, butter | Muddy water, sand in water |
Solution particles
So small that they neither settle nor scatter enough light to make its path visible.
Colloidal particles
Intermediate in size; they remain dispersed and scatter light.
Suspended particles
Large enough to scatter light, settle under gravity and be trapped by ordinary filtration.
Colloids, Emulsions, Tyndall Effect and Alloys
Four linked ideas that frequently appear in reasoning questions.
Dispersed phase
The solute-like particles present in smaller quantity.
Milk: fat droplets
Fog: water droplets
Dispersion medium
The continuous phase in which particles are distributed.
Milk: water
Fog: air
Emulsions
| Emulsion type | Dispersed phase | Dispersion medium | Examples |
|---|---|---|---|
| Oil-in-water (O/W) | Oil/fat droplets | Water | Milk, vanishing cream |
| Water-in-oil (W/O) | Water droplets | Oil/fat | Butter, cold cream |
Tyndall effect
Examples: headlights in fog, a sunbeam through a dusty room, sunlight through a dense tree canopy and stadium floodlights.
Alloys
| Alloy | Main components | Why it is useful | Examples of use |
|---|---|---|---|
| Brass | Copper + zinc | Strong, workable and corrosion-resistant | Fittings, instruments, utensils |
| Bronze | Copper + tin | Harder than copper | Sculptures, coins, bearings |
NCERT Activity Capsules
Aim, observation and conclusion in exam-friendly form.
Copper sulphate crystallisation
Aim: Obtain pure crystals from a saturated solution.
Observation: Shiny blue, well-shaped crystals appear on slow cooling.
Conclusion: Crystallisation purifies a solid using temperature-dependent solubility.
Salt from seawater
Process: Seawater is held in shallow ponds; sun and wind evaporate water.
Observation: The concentrated solution becomes saturated and salt crystallises.
Conclusion: Evaporation followed by crystallisation yields salt.
Chromatography of black ink
Aim: Separate the colours in black ink.
Observation: Different coloured spots travel to different heights.
Conclusion: Black ink is a mixture of dyes with different affinities for paper and solvent.
Oil and water
Aim: Separate immiscible liquids with a separating funnel.
Observation: Water forms the lower layer; oil forms the upper layer.
Conclusion: Density difference enables layer-wise separation.
Camphor and sand
Aim: Separate a sublimable solid.
Observation: Camphor vapour deposits on the cool funnel; sand remains.
Conclusion: Sublimation separates camphor from non-sublimable sand.
Simple centrifuge model
Aim: Study separation by rapid spinning.
Observation: Denser particles move farther outward than lighter liquid.
Conclusion: Centrifugation speeds density-based separation.
Sticky-Note Revision Wall
High-value facts to revise just before a test.
Formula Check
Always divide by the amount of solution, not only solvent. First calculate total mass/volume if needed.
Particle Sizes
Solution < 1 nm
Colloid = 1–1000 nm
Suspension > 1000 nm
Filter Test
Suspensions are usually separable by ordinary filtration. True solutions and colloids are not.
Light Test
Colloids and suspensions show the Tyndall effect. True solutions do not.
Distillation Clue
Need the liquid back? Think distillation. A large boiling-point gap favours simple distillation.
Crystals Clue
Need a pure solid? Prepare a hot saturated solution, filter and cool slowly.
Layer Clue
Immiscible liquids + different densities = separating funnel; drain the denser lower layer first.
Complex Mixtures
Use methods in sequence. Separate the component with the most distinctive property first.
Important Questions and Answers
Tap any question to reveal its answer. Questions progress from recall to application.
Very Short Answer
1. What is a mixture?
A mixture is a physical combination of two or more substances in any proportion. The components are not chemically combined and retain their characteristic properties.
2. Name the solute and solvent in a sugar solution.
Sugar is the solute and water is the solvent.
3. What is the size range of colloidal particles?
In this chapter, colloidal particles are taken as approximately 1–1000 nm in size.
4. What is the liquid collected after condensation in distillation called?
It is called the distillate.
5. Which method separates camphor from sand?
Sublimation, because camphor sublimes while sand does not.
6. What is a coagulant? Give one example.
A coagulant is a substance that causes very fine particles to clump into larger flocs. Alum (fitkari) is a common example.
Short Answer and Reasoning
7. Differentiate between homogeneous and heterogeneous mixtures.
A homogeneous mixture has uniform composition throughout and appears as one phase, such as salt solution or brass. A heterogeneous mixture has non-uniform composition or more than one phase, such as muddy water or oil and water.
8. Why do mud particles settle in water but milk particles do not?
Muddy water is a suspension containing large, heavy particles that settle under gravity. Milk is a colloid; its much smaller droplets remain dispersed and do not settle on standing.
9. How is evaporation different from boiling?
Evaporation is a slow surface process that can occur at any temperature. Boiling is a rapid bulk process that occurs throughout a liquid at its fixed boiling point.
10. Why does salt solution not show the Tyndall effect, while milk does?
Salt solution is a true solution whose particles are smaller than 1 nm and do not scatter enough light to show its path. Milk contains colloidal droplets large enough to scatter light, so it shows the Tyndall effect.
11. Why is slow cooling preferred during crystallisation?
Slow cooling gives solute particles enough time to arrange in a regular pattern, producing larger and better-shaped crystals. Rapid cooling usually gives smaller, less well-formed crystals.
12. Why is crystallisation often better than evaporation for purifying a solid?
Crystallisation produces purer crystals, leaves many soluble impurities in the mother liquor and prevents the solute from being heated to complete dryness, which could decompose some substances.
13. Why can oil and water be separated with a separating funnel?
Oil and water are immiscible and have different densities. They form two layers; the denser water lies below and can be drained first through the stopcock.
14. State the principle of paper chromatography.
It is based on the different affinities or distributions of components between a stationary phase (paper) and a mobile phase (solvent). Components therefore travel at different speeds and separate.
Solved Numericals
15. A talcum powder contains 4% m/m zinc oxide. Find the zinc oxide in 300 g powder.
Mass of zinc oxide = (4 ÷ 100) × 300 g
= 12 g.
16. Calculate % m/m when 20 g sugar is dissolved in 80 g water.
Mass of solution = 20 + 80 = 100 g.
% m/m = (20 ÷ 100) × 100 = 20%.
17. A hospital solution contains 0.9 g salt in 100 mL solution. Express its concentration.
% m/V = (0.9 g ÷ 100 mL) × 100 = 0.9% m/V.
18. An alloy contains 70% copper by mass. Find copper and zinc in 120 g alloy.
Mass of copper = (70 ÷ 100) × 120 = 84 g.
Mass of zinc = 120 − 84 = 36 g.
19. Compare three sugar solutions: A = 20 g sugar + 80 g water; B = 20 g + 100 g; C = 30 g + 80 g. Which is most concentrated?
A: (20 ÷ 100) × 100 = 20%
B: (20 ÷ 120) × 100 = 16.67%
C: (30 ÷ 110) × 100 = 27.27%
Therefore, solution C is the most concentrated.
Application and HOTS
20. Separate a mixture of naphthalene, common salt and sand. Give the correct sequence and reason.
- Sublimation: heat gently so naphthalene sublimes and deposits on a cool surface.
- Dissolution: add water to the remaining salt and sand; salt dissolves.
- Filtration: sand remains as residue; salt solution passes as filtrate.
- Evaporation/crystallisation: recover common salt from the filtrate.
Each step uses a different property: sublimability, solubility and volatility.
21. Liquids A and B boil at 60°C and 90°C. Suggest a method and explain.
Use simple distillation. Their boiling points differ by 30°C, so A vaporises first. Its vapour is cooled in a condenser and collected separately, while most of B remains in the flask.
22. A beam of light is passed through salt solution, starch solution and muddy water. Predict the observations.
- Salt solution: beam path is not visible; no Tyndall effect.
- Starch solution: beam path is visible because it is colloidal.
- Muddy water: beam path is visible due to suspended particles; these particles later settle.
23. Why would blood circulation be affected if blood behaved like an ordinary suspension?
Its cellular components would settle under gravity, causing uneven composition, possible blockages and failure to transport oxygen, nutrients and wastes uniformly. Blood must keep its components dispersed while circulating.
24. Choose the best method: obtain salt from seawater, obtain pure copper sulphate crystals, and obtain pure water from salt solution.
- Salt from seawater: evaporation, because water need not be recovered.
- Pure copper sulphate crystals: crystallisation, because pure crystals are required.
- Pure water from salt solution: distillation, because the solvent must be recovered.
25. Assertion–Reason: True solutions do not show the Tyndall effect because their particles are larger than 1000 nm.
The assertion is true, but the reason is false. True-solution particles are extremely small—less than 1 nm—not larger than 1000 nm. They do not scatter enough light to make the beam path visible.
Case-Based Question
26. A village water tank contains very fine suspended clay. Settling and cloth filtration do not clear it fully. Suggest a treatment sequence and explain each step.
Add a suitable amount of alum to cause coagulation. The tiny clay particles join into larger flocs. Allow these flocs to settle by sedimentation, pour off the clearer upper water by decantation, and finally use filtration. Each stage makes the next stage more effective.
Definition Bank
Concise, exam-ready meanings of every major term.
| Term | Definition |
|---|---|
| Mixture | Physical combination of two or more substances in any proportion. |
| Homogeneous mixture | Mixture with uniform composition throughout. |
| Heterogeneous mixture | Mixture with non-uniform composition. |
| Solution | Homogeneous mixture of solute and solvent. |
| Solute | Substance that dissolves in a solvent. |
| Solvent | Substance that dissolves the solute. |
| Concentration | Amount of solute in a given amount of solution or solvent. |
| Solubility | Maximum amount of solute that dissolves in a fixed amount of solvent at a given temperature. |
| Saturated solution | Solution unable to dissolve more solute at a given temperature. |
| Unsaturated solution | Solution capable of dissolving more solute at a given temperature. |
| Solubility curve | Graph of solubility against temperature. |
| Evaporation | Slow surface conversion of a liquid into vapour at temperatures below its boiling point. |
| Crystallisation | Formation of pure solid crystals from a solution, commonly by cooling a hot saturated solution. |
| Crystal | Solid whose particles are arranged in a regular geometric pattern. |
| Distillation | Separation by vaporising a liquid and condensing its vapour. |
| Distillate | Condensed liquid collected during distillation. |
| Chromatography | Separation based on different movements of components between stationary and mobile phases. |
| Miscible liquids | Liquids that mix completely in all proportions. |
| Immiscible liquids | Liquids that do not mix and form separate layers. |
| Sublimation | Direct conversion of a solid into vapour without passing through the liquid state. |
| Deposition | Direct conversion of vapour into solid. |
| Centrifugation | Separation of components of different densities by rapid spinning. |
| Coagulation | Process of making fine particles clump into larger flocs. |
| Coagulant | Substance added to bring about coagulation. |
| Suspension | Heterogeneous mixture with large particles that settle on standing. |
| Colloid | Heterogeneous mixture with intermediate-sized particles that remain dispersed. |
| Dispersed phase | Colloidal particles distributed through a medium. |
| Dispersion medium | Continuous phase in which colloidal particles are dispersed. |
| Emulsion | Colloid in which both phases are liquids. |
| Emulsifying agent | Substance that stabilises an emulsion. |
| Tyndall effect | Scattering of light by colloidal or suspended particles, making the beam path visible. |
| Alloy | Homogeneous solid mixture of metals, or a metal and a non-metal. |
One-Minute Chapter Recap
Classify
Uniform = homogeneous. Non-uniform = heterogeneous. A colloid only appears uniform.
Calculate
Concentration = amount of solute ÷ amount of solution × 100. Match mass/volume units.
Separate
Choose by property: size, density, solubility, boiling point, sublimability or affinity.
Compare
Solutions do not scatter light; colloids scatter but do not settle; suspensions scatter and settle.
Purify
Evaporation gets a solid, crystallisation gets purer crystals, distillation recovers a liquid.
Apply
Real uses include ORS, water treatment, blood separation, dairy processing, perfumes and alloys.
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