🧪 Chemistry · Class 9
Chapter 5: Exploring Mixtures and their Separation
From sugarcane to sugar crystals — the fascinating science of separating mixtures!
Homogeneous Mixtures
Heterogeneous Mixtures
Solutions & Concentration
Crystallization
Distillation
Chromatography
Colloids & Tyndall Effect
Sublimation
Heterogeneous Mixtures
Solutions & Concentration
Crystallization
Distillation
Chromatography
Colloids & Tyndall Effect
Sublimation
📚 Contents
Chapter Introduction & Overview
Have you ever wondered how white sugar crystals are obtained from tall green sugarcane plants? Or how doctors detect diseases like malaria using just a few drops of blood? All of this is possible because of the science of separating mixtures!
What is a Mixture?
A mixture is formed when two or more substances are combined without any chemical reaction. The substances in a mixture can be separated by physical methods.
A mixture is formed when two or more substances are combined without any chemical reaction. The substances in a mixture can be separated by physical methods.
🔍 Why Do We Need to Separate Mixtures?
- To get pure substances for laboratory experiments
- To remove impurities (e.g., purifying water)
- For industrial processes like making sugar, petroleum refining
- For medical purposes — separating blood components
- Environmental applications — treating sewage water
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Did You Know?Our kidneys perform separation every day — they filter waste products from blood and excrete them as urine. Nature is the best chemist!
🗺️ Chapter Roadmap
🧪 Types of MixturesHomogeneous vs Heterogeneous; Solutions, Suspensions, Colloids
📐 ConcentrationMass/mass %, Mass/volume %, Volume/volume %
🔬 Separation MethodsCrystallization, Distillation, Chromatography, Sublimation
💡 Tyndall EffectScattering of light by colloids and suspensions
How Can We Classify Mixtures?
Mixtures are broadly classified into two types based on their uniformity:
🟢 Homogeneous Mixture (सम मिश्रण)
Uniform composition throughout. You cannot distinguish the individual components. Also called a Solution.
Uniform composition throughout. You cannot distinguish the individual components. Also called a Solution.
Examples: Sugar in water, salt water, vinegar, aerated drinks (soda), brass alloy
🔴 Heterogeneous Mixture (असम मिश्रण)
Non-uniform composition. Components are visible and can be distinguished.
Non-uniform composition. Components are visible and can be distinguished.
Examples: Sand in water, oil and water, muddy water, smoke, fog
🔦 The Laser Light Test (Tyndall Effect Test)
When laser light is passed through different mixtures, the results differ:
| Mixture | Laser Path Visible? | Type | Settles? |
|---|---|---|---|
| Salt + Water | ❌ Not visible | Solution (Homogeneous) | No |
| Chalk + Water | ✅ Visible (bright) | Suspension (Heterogeneous) | Yes |
| Milk + Water | ✅ Visible (faint) | Colloid | No |
NCERT Definition — Homogeneous Mixture:
A mixture that has a uniform composition throughout is called a homogeneous mixture or a solution. A solution always remains homogeneous.
A mixture that has a uniform composition throughout is called a homogeneous mixture or a solution. A solution always remains homogeneous.
📊 Comparing Solutions, Suspensions, and Colloids
| Property | Solution | Suspension | Colloid |
|---|---|---|---|
| Nature | Homogeneous | Heterogeneous | Appears homogeneous |
| Particle Size | <1 nm | >1000 nm | 1–1000 nm |
| Visibility | Not visible | Visible (naked eye) | Not visible (naked eye) |
| Settles? | No | Yes (on standing) | No |
| Filtration | Cannot separate | Can separate | Cannot separate by regular filter |
| Tyndall Effect | ❌ No | ✅ Yes | ✅ Yes |
| Examples | Salt solution, copper sulfate solution | Sand in water, muddy water | Milk, blood, fog |
Solutions & Concentration
A solution is a homogeneous mixture of a solute (the substance that dissolves) and a solvent (the substance that dissolves the solute).
Key Terms:
Solute (विलेय) — the substance dissolved (e.g., sugar, salt). Solvent (विलायक) — the substance that dissolves (e.g., water). Concentration (सांद्रता) — amount of solute in a given amount of solution.
Solute (विलेय) — the substance dissolved (e.g., sugar, salt). Solvent (विलायक) — the substance that dissolves (e.g., water). Concentration (सांद्रता) — amount of solute in a given amount of solution.
📏 Expressing Concentration — Three Methods
A. 🟦 Mass by Mass Percentage (% m/m or % w/w)
Tells us how many grams of solute are present in 100 grams of the total solution. Used for solid-in-solid or solid-in-liquid mixtures (e.g., milk powder, spice mixtures, food labels).
Mass by Mass % = (Mass of Solute / Mass of Solution) × 100
Example: 10 g salt dissolved in 90 g water.
Mass of solution = 10 + 90 = 100 g
% m/m = (10 / 100) × 100 = 10% m/m
Mass of solution = 10 + 90 = 100 g
% m/m = (10 / 100) × 100 = 10% m/m
B. 🟩 Mass by Volume Percentage (% m/v or % w/v)
Tells us how many grams of solute are present in 100 mL of solution. Used in medicines and laboratories (e.g., 5% glucose IV solution, 0.9% saline drip).
Mass by Volume % = (Mass of Solute in g / Volume of Solution in mL) × 100
Example: 5 g glucose dissolved to make 100 mL solution.
% m/v = (5 / 100) × 100 = 5% m/v
% m/v = (5 / 100) × 100 = 5% m/v
C. 🟧 Volume by Volume Percentage (% v/v)
Tells us how many mL of solute are present in 100 mL of solution. Used when two liquids are mixed (e.g., vinegar = 5% v/v acetic acid, perfumes, cosmetics).
Volume by Volume % = (Volume of Solute in mL / Volume of Solution in mL) × 100
Example: 1 mL pesticide in 100 mL spray solution.
% v/v = (1 / 100) × 100 = 1% v/v
% v/v = (1 / 100) × 100 = 1% v/v
🌡️ Solubility of Substances
Solubility (विलेयता): The maximum amount of solute that can dissolve in 100 g (or 100 mL) of solvent at a given temperature. A solution that has dissolved the maximum possible solute is called a saturated solution (संतृप्त विलयन).
- Solubility of solid solutes in liquids generally increases with temperature
- Solubility of gases in liquids generally decreases with temperature (that’s why hot soda loses fizz!)
Meet a Scientist — Dilip Mahalanabis
An Indian paediatrician who first developed and implemented ORS (Oral Rehydration Solution) for treating dehydration from diseases like cholera and diarrhoea. His formula, containing specific amounts of salt and sugar, was adopted by WHO and has saved millions of lives worldwide. Note: ORS is NOT the same as any sugary drink — the proportions matter!
An Indian paediatrician who first developed and implemented ORS (Oral Rehydration Solution) for treating dehydration from diseases like cholera and diarrhoea. His formula, containing specific amounts of salt and sugar, was adopted by WHO and has saved millions of lives worldwide. Note: ORS is NOT the same as any sugary drink — the proportions matter!
Hospital Saline Drip Fact:
The saline drip (IV fluid) used in hospitals contains 0.9% m/v sodium chloride (common salt) in water. This is called “normal saline” and is safe for blood because it matches blood’s salt concentration.
The saline drip (IV fluid) used in hospitals contains 0.9% m/v sodium chloride (common salt) in water. This is called “normal saline” and is safe for blood because it matches blood’s salt concentration.
Separating Homogeneous Mixtures
Homogeneous mixtures look uniform, so separating them requires special techniques based on the physical properties of their components.
💎 5.3.1 Crystallization (क्रिस्टलीकरण)
Crystallization is the process of forming pure solid crystals from a saturated solution by changing temperature. It is used for purification of solids and separation of mixtures.
Principle: When a hot saturated solution is cooled, its solubility decreases. The excess solute crystallises out as pure crystals, leaving impurities in the solution.
🧪 Steps to Grow Copper Sulfate Crystals:
- Add copper sulfate to 25 mL water with a drop of dilute H₂SO₄; heat gently in a water bath
- Keep adding copper sulfate until the solution is saturated (no more dissolves)
- Filter the hot saturated solution to remove insoluble impurities
- Allow the filtrate to cool slowly without disturbing
- Large, shiny, blue crystals of copper sulfate form as it cools
- Filter, rinse with cold water, and dry on a watch glass
Safety First!
Copper sulfate is toxic — do not touch with bare hands. Always perform under adult supervision. Sulfuric acid is corrosive — handle very carefully!
Copper sulfate is toxic — do not touch with bare hands. Always perform under adult supervision. Sulfuric acid is corrosive — handle very carefully!
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Crystals in Everyday Life!Rock salt (sendha namak), candy sugar (mishri — मिश्री), snowflakes, and frost on windows are all crystals! Even the Mawsmai Cave in Cherrapunji (Sohra), Meghalaya, has spectacular natural crystal formations.
India’s Scientific Contributions — Ancient Salt Crystallization
Coastal communities in India used crystallization of salt for thousands of years. Panga salt was made by boiling concentrated sea brines, while karkatch salt was produced by evaporating seawater. Different crystal sizes were produced by controlling the process — a remarkable ancient technology!
Coastal communities in India used crystallization of salt for thousands of years. Panga salt was made by boiling concentrated sea brines, while karkatch salt was produced by evaporating seawater. Different crystal sizes were produced by controlling the process — a remarkable ancient technology!
🌡️ 5.3.2 Distillation (आसवन)
Distillation separates miscible liquids or a liquid from a solution with dissolved solids, using differences in boiling points.
Principle: The liquid with the lower boiling point vaporises first. Vapours pass through a condenser where they cool and convert back to liquid (distillate), which is collected in a separate flask.
Used when: Difference in boiling points ≥ 25°C
| Substance | Boiling Point |
|---|---|
| Water | 100°C |
| Acetone | 56°C |
| Alcohol (ethanol) | 78°C |
| Chloroform | 61°C |
| Benzene | 80°C |
🔧 Apparatus: Distillation Set-Up
- Distillation flask — holds the mixture (e.g., acetone + water)
- Thermometer — measures temperature of vapours
- Water condenser — cools the vapours (water flows in from bottom, out from top)
- Conical flask — collects the distillate (purified liquid)
India’s Scientific Heritage — Kannauj & Mitti ka Ittar
Kannauj in Uttar Pradesh is known as the Perfume Capital of India. The earthy fragrance after first rain is captured using a traditional distillation method called the Deg-Bhapka method — passed down through generations. This natural perfume is called Mitti ka Ittar (earthy fragrance) and is in demand globally!
Kannauj in Uttar Pradesh is known as the Perfume Capital of India. The earthy fragrance after first rain is captured using a traditional distillation method called the Deg-Bhapka method — passed down through generations. This natural perfume is called Mitti ka Ittar (earthy fragrance) and is in demand globally!
Fractional Distillation — Petroleum Refining
When components differ by less than 25°C in boiling points, fractional distillation is used. Crude petroleum is separated this way into: Petroleum gas → Petrol → Aviation fuel (Kerosene) → Diesel → Lubricating oil → Bitumen (road making).
When components differ by less than 25°C in boiling points, fractional distillation is used. Crude petroleum is separated this way into: Petroleum gas → Petrol → Aviation fuel (Kerosene) → Diesel → Lubricating oil → Bitumen (road making).
🎨 5.3.3 Paper Chromatography (कागज़ वर्णलेखन)
Paper chromatography separates components of a mixture based on differences in how fast they move up a paper when carried by a solvent.
Principle: Different substances travel at different speeds through the paper with the solvent. Substances that interact more with the paper move slowly; those attracted more to the solvent move faster.
🧪 Steps for Paper Chromatography:
- Take a strip of chromatographic (or filter) paper, draw a horizontal pencil line 2 cm from the bottom
- Place a spot of black ink (or other mixture) at the centre of the pencil line
- Place the strip vertically in a beaker/gas jar with a thin layer of water — the water level must be BELOW the ink spot
- Watch as water rises through the paper — the ink separates into different coloured bands!
Common Mistake Alert!
The solvent level must be BELOW the sample spot. If the spot touches the solvent directly, it will dissolve away instead of separating by capillary action.
The solvent level must be BELOW the sample spot. If the spot touches the solvent directly, it will dissolve away instead of separating by capillary action.
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Word Origin!The word “chromatography” comes from Greek: chroma (colour) + graphein (to write) = “writing with colour”! It was first used to separate coloured plant pigments by Russian botanist Mikhail Tsvet in 1900.
🔬 Applications of Paper Chromatography:
- Detecting ink components (e.g., black ink separates into blue, red, yellow bands)
- Separating pigments in spinach leaves
- Separating pigments from flower petals
- Forensic science — ink analysis on documents
- Food colour analysis
Separating Heterogeneous Mixtures
Heterogeneous mixtures have different components that can often be separated using their physical differences like density, size, or state change.
⚗️ 5.4.1 Separating Funnel — Immiscible Liquids
Immiscible liquids (अमिश्रणीय द्रव) do not mix and form separate layers. They are separated using a separating funnel.
Principle: Immiscible liquids of different densities form separate layers. The denser liquid sinks to the bottom; the less dense liquid floats on top. Opening the stopcock drains the lower layer first.
🟡 Mustard Oil + WaterOil (less dense) forms upper layer. Water (more dense) forms lower layer. Open stopcock → drain water first → close → drain oil separately.
🌊 Oil + Water in OceanOil spills float on seawater because oil is less dense than water. Same principle — density difference causes layer formation.
🔥 5.4.2 Sublimation (ऊर्ध्वपातन)
Sublimation is when a solid directly changes into vapour (without becoming a liquid first) upon heating. On cooling, the vapour changes directly back to solid — this is called deposition.
Sublimable substances: Camphor (कपूर), naphthalene, ammonium chloride, iodine, dry ice (solid CO₂). These substances can be separated from non-sublimable ones like sand, salt, etc.
🧪 Separating Camphor from Sand:
- Take the camphor + sand mixture in a china dish on a tripod stand
- Cover with an inverted glass funnel (nozzle plugged with cotton)
- Heat gently — camphor sublimes and vapours rise
- Camphor deposits as white solid on the inner walls of the funnel
- Sand remains behind in the china dish
🌀 5.4.3 Suspensions & How to Separate Them
Suspension (निलंबन): A heterogeneous mixture where solid particles (size >1000 nm) remain suspended in a liquid medium. Particles are visible to the naked eye and settle on standing.
For very fine suspended particles that don’t settle easily, two advanced methods are used:
🌀 A. Centrifugation (अपकेंद्रण)
- The mixture is spun at high speed in a centrifuge machine
- Centrifugal force (outward force) pushes heavier particles to the bottom of the tube
- Lighter liquid remains at the top
- Applications: Separating blood components (plasma, RBCs, platelets), dairy industry (separating cream from milk), chemical industries
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The Paperfuge — Innovation!Scientists designed a hand-powered centrifuge called a paperfuge using just cardboard and string — inspired by a spinning toy! It can spin blood samples fast enough to diagnose malaria and anaemia in remote areas without electricity. Science saves lives!
🪨 B. Coagulation (स्कंदन)
- A coagulant (like powdered alum / फिटकरी) is added to muddy water
- Alum causes fine suspended particles to clump together (coagulate)
- Larger clumps settle by gravity (sedimentation)
- Clear water is separated by decantation or filtration
- Everyday example: Making paneer — lemon juice/vinegar coagulates milk proteins!
🔗 Alloys — A Special Case
An alloy is a homogeneous mixture of two or more metals (or a metal and non-metal). Physical methods cannot separate alloy components.
| Alloy | Components | Uses |
|---|---|---|
| Brass (पीतल) | ~80% Copper + ~20% Zinc | Utensils, musical instruments |
| Bronze (कांसा) | ~80% Copper + ~20% Tin | Statues, coins, bells |
| Stainless Steel | Iron + Carbon + Chromium + Nickel + Molybdenum | Cutlery, surgical instruments |
Colloids & the Tyndall Effect
🌫️ What is a Colloid?
A colloid is a mixture where particles of the dispersed phase (1–1000 nm) are evenly distributed throughout the dispersion medium. Colloid particles don’t settle and are not visible to the naked eye, but they can scatter light!
🥛 Everyday ColloidsMilk, blood, fog, smoke, ice cream, tomato sauce, butter, cold cream, body lotion, vanishing cream
📐 Particle SizeSolution: <1 nm
Colloid: 1–1000 nm
Suspension: >1000 nm
Colloid: 1–1000 nm
Suspension: >1000 nm
💡 Tyndall Effect (टिंडल प्रभाव)
Tyndall Effect: The scattering of a light beam by particles in a colloid or suspension, making the path of light visible. It does NOT occur in true solutions (particles too small to scatter light). Named after scientist John Tyndall.
🔦 Examples of Tyndall Effect:
- Sunbeams visible through forest gaps (dust particles in air scatter light)
- Headlights visible in fog
- Floodlights in a sports stadium appear as visible beams
- Light entering a dark room through a small hole
- Laser passed through milk (visible beam) vs. salt solution (no visible beam)
🧴 Emulsions — Special Colloids
When both the dispersed phase and dispersion medium are liquids, the colloid is called an emulsion.
💧 Oil-in-Water EmulsionOil droplets dispersed in water.
Examples: Milk, vanishing cream, some medicines
Examples: Milk, vanishing cream, some medicines
🧈 Water-in-Oil EmulsionWater droplets dispersed in oil.
Examples: Butter, cold cream, body lotion
Examples: Butter, cold cream, body lotion
Emulsifying Agents:
Emulsions are stabilised by emulsifying agents. For example, proteins in milk stabilise it as a colloid. You can make a simple emulsion at home by shaking cooking oil with water + a few drops of soap solution — soap acts as an emulsifying agent!
Emulsions are stabilised by emulsifying agents. For example, proteins in milk stabilise it as a colloid. You can make a simple emulsion at home by shaking cooking oil with water + a few drops of soap solution — soap acts as an emulsifying agent!
🩸 Blood — A Remarkable Colloid
Blood is a colloid! Blood cells (dispersed phase) are suspended in plasma (dispersion medium). That’s why blood doesn’t settle in vessels — unlike a suspension. Centrifugation separates blood into: Plasma (top) → Platelets + WBCs (middle) → RBCs (bottom).
Donate Blood, Save Lives!
Donated blood is separated into components (plasma, platelets, WBCs, RBCs) and stored in blood banks. The body replaces donated blood naturally within a few weeks. Do you know your blood group?
Donated blood is separated into components (plasma, platelets, WBCs, RBCs) and stored in blood banks. The body replaces donated blood naturally within a few weeks. Do you know your blood group?
Quick Revision Summary
Homogeneous vs HeterogeneousUniform composition = Homogeneous (solution); Non-uniform = Heterogeneous
Solution, Colloid, SuspensionParticle size: Solution <1nm, Colloid 1–1000nm, Suspension >1000nm
Concentration Formulae% m/m, % m/v, % v/v — all = (part/total) × 100
CrystallizationCool hot saturated solution → excess solute forms crystals. Used for purification.
DistillationSeparate miscible liquids with boiling point difference ≥ 25°C. Lower BP liquid vaporises first.
Paper ChromatographySeparates by rate of movement on paper; spot must be above solvent level.
Separating FunnelSeparates immiscible liquids based on density. Denser liquid sinks to bottom.
SublimationSolid → Vapour (no liquid stage). Camphor, naphthalene, dry ice sublimate.
CentrifugationHigh-speed spinning separates heavier particles from lighter liquid in a suspension.
CoagulationAlum (fitkari) clumps fine particles → settle by gravity. Used in water purification.
Tyndall EffectScattering of light by colloid/suspension particles. NOT shown by solutions.
AlloysHomogeneous metal mixtures (brass, bronze, steel). Cannot be separated by physical methods.
Important Exam Questions
Q1. What is the difference between a homogeneous and a heterogeneous mixture? Give two examples of each. (CBSE Type / 3 Marks)
Ans: A homogeneous mixture has uniform composition throughout — you cannot see separate components. Examples: salt solution, vinegar. A heterogeneous mixture has non-uniform composition — components are visibly different. Examples: muddy water, sand in water.
Q2. If 10 g of salt is dissolved in 90 g of water, calculate the mass by mass percentage (% m/m) of the solution. (CBSE Type / 2 Marks)
Ans: Mass of solute (salt) = 10 g. Mass of solvent (water) = 90 g. Total mass of solution = 10 + 90 = 100 g.
% m/m = (Mass of solute / Mass of solution) × 100 = (10/100) × 100 = 10% m/m
% m/m = (Mass of solute / Mass of solution) × 100 = (10/100) × 100 = 10% m/m
Q3. What is the Tyndall Effect? Why does a solution not show the Tyndall Effect but a colloid does? (CBSE Type / 3 Marks)
Ans: The Tyndall Effect is the scattering of a beam of light by particles in a colloid or suspension, making the light path visible. In a solution, particles are extremely small (less than 1 nm) and cannot scatter light. In a colloid, particles are larger (1–1000 nm) and can scatter the light beam, making it visible from the side.
Q4. Explain the process of distillation with a labelled diagram. Under what conditions is it preferred over simple evaporation? (CBSE Type / 5 Marks)
Ans: Distillation separates miscible liquids or a liquid from dissolved solids by heating the mixture. The component with the lower boiling point vaporises first. Vapours pass through a water-cooled condenser and are collected as pure liquid (distillate) in a conical flask. Apparatus: Distillation flask → Thermometer → Water condenser (water in from bottom, out at top) → Conical flask.
Distillation is preferred: (1) when you want to recover the solvent (not just the solute), (2) when separating two miscible liquids with boiling point difference ≥ 25°C, (3) example: acetone (56°C) and water (100°C).
Distillation is preferred: (1) when you want to recover the solvent (not just the solute), (2) when separating two miscible liquids with boiling point difference ≥ 25°C, (3) example: acetone (56°C) and water (100°C).
Q5. How are suspensions different from colloids? How can you distinguish between the two using a simple experiment? (CBSE Type / 3 Marks)
Ans: Suspensions have particle size greater than 1000 nm — particles are visible, settle on standing, and can be separated by filtration. Colloids have particle size 1–1000 nm — particles are not visible, do not settle, and cannot be separated by normal filtration. Distinguishing experiment: Shine a laser through both — both show the Tyndall Effect. But leave them undisturbed for some time — suspension settles at the bottom while colloid remains stable (does not settle).
Q6. State any three differences between evaporation and distillation. (CBSE Type / 3 Marks)
Ans: (1) In evaporation, the solvent is lost; in distillation, the solvent is recovered as distillate. (2) Evaporation is suitable for getting solute from solution; distillation is used to get pure solvent or to separate two miscible liquids. (3) Evaporation is a simpler process done in an open vessel; distillation requires a closed apparatus with a condenser.
Final Exam Tips for Chapter 5!
1. Always learn ALL THREE concentration formulas (% m/m, % m/v, % v/v) with solved examples. 2. Remember the condition for distillation: boiling point difference ≥ 25°C. 3. The Tyndall Effect is a very common MCQ and 1-mark question. 4. Crystallization = based on SOLUBILITY differences at different temperatures. 5. For paper chromatography: solvent level must always be BELOW the spot. 6. Alloys cannot be separated by physical methods — a frequently asked fact! Best of luck! 🌟
1. Always learn ALL THREE concentration formulas (% m/m, % m/v, % v/v) with solved examples. 2. Remember the condition for distillation: boiling point difference ≥ 25°C. 3. The Tyndall Effect is a very common MCQ and 1-mark question. 4. Crystallization = based on SOLUBILITY differences at different temperatures. 5. For paper chromatography: solvent level must always be BELOW the spot. 6. Alloys cannot be separated by physical methods — a frequently asked fact! Best of luck! 🌟
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