🧪
Class 9 Science · Chapter 5 · Part 1 of 2

Exploring Mixtures and their Separation

Homogeneous/Heterogeneous Mixtures · Solutions · Concentration · Crystallization · Distillation · Chromatography

⚗️ Solutions
📊 Concentration
💎 Crystallization
🔥 Distillation
🎨 Chromatography
PART 1
This part covers: Classifying Mixtures → Solutions → Concentration (Mass/Volume %) → Solubility → Crystallization → Distillation → Paper Chromatography. Part 2 covers Heterogeneous Mixtures, Colloids & Tyndall Effect.
📌 Jump to Section
Classify Mixtures
Solutions
Concentration
Solubility
Crystallization
Distillation
Chromatography
Definitions
Exam FAQs

🔍 5.1 How Can We Classify Mixtures?

📖 Two Types of Mixtures

Homogeneous Mixture (Solution) — Has a uniform composition throughout. A well-stirred sugar-water mixture is equally sweet in first and last sip. Examples: vinegar, soda (aerated drinks).

Heterogeneous Mixture — NOT uniform; components are visible and may settle with time. Example: sand and water (sand settles, visible particles).

🧪 Activity 5.1 — Group Activity (Laser Light Test)
Group A

Common salt + water (stirred). Salt dissolves completely — particles NOT visible.

Group B

Chalk powder + water (stirred). Particles ARE visible, settle over time.

Group C

Milk + water (stirred). Looks uniform but scatters laser light!

Laser Test

A: light path NOT visible. B & C: light path IS visible (scattered).

Filtration

A: no residue. B: residue left. C: no residue (but not a true solution either!)

Conclusion

A = solution, B = suspension (heterogeneous), C = colloid (different from both!)

⚗️ 5.2 Solutions

📖 Definition

Solution — A homogeneous mixture of a solute (substance that gets dissolved) and a solvent (substance that dissolves the solute). Example: In sugar-water, sugar = solute, water = solvent.

👨‍⚕️
Dilip Mahalanabis — Meet a Scientist

Indian paediatrician who first developed and implemented the treatment for dehydration caused by diarrhoea and cholera. He formulated ORS (Oral Rehydration Solution), which revolutionised rehydration therapy and has saved millions of lives after WHO popularised it worldwide.

⭐ Why Proportion Matters

ORS requires exact proportions of salt and sugar in fixed water — changing amounts won’t make proper ORS. Similarly, pesticides need correct concentration: too little won’t protect crops, too much damages crops/soil/environment.

📊 5.2.1 & 5.2.2 Concentration of a Solution

📖 Definition

Concentration — The amount of solute dissolved in a given amount of solvent or solution.

Three Ways to Express Concentration (%)

Method	Used For	Tells Us
Mass by Mass % (% m/m)	Homogeneous & heterogeneous (milk powder, packaged food)	Grams of solute per 100g of solution
Mass by Volume % (% m/v)	Medicines, lab solutions (e.g. 5% glucose)	Grams of solute per 100mL of solution
Volume by Volume % (% v/v)	Miscible liquids (perfumes, vinegar)	mL of solute per 100mL of solution

Eq 5.1 — Mass by Mass %
% m/m = (Mass of solute ÷ Mass of solution) × 100
Eq 5.2 — Mass by Volume %
% m/v = (Mass of solute ÷ Volume of solution) × 100
Eq 5.3 — Volume by Volume %
% v/v = (Volume of solute ÷ Volume of solution) × 100
📝 Example 5.1 — Mass by Mass %

10g salt dissolved in 90g water. Total mass = 100g.

% m/m = (10 ÷ 100) × 100 = 10% m/m
📝 Example 5.2 — Mass by Volume %

5g glucose dissolved to make 100mL solution.

% m/v = (5 ÷ 100) × 100 = 5% m/v
📝 Example 5.3 — Volume by Volume %

1mL pesticide mixed to make 100mL spray.

% v/v = (1 ÷ 100) × 100 = 1% v/v
💡 Important Note

Industries commonly use weight by weight % (% w/w) — numerically equal to % m/m, since weight and mass are used interchangeably.

🔩 Threads of Curiosity — Saline Drip

A saline drip in hospitals is usually 0.9% m/v sodium chloride in water = 0.9g salt per 100mL solution. This concentration is safe for blood and replaces lost body fluids.

✅ Check Your Understanding — Solutions & Concentration
Q1. In a sugar-water solution, sugar is called the:
ASolute
BSolvent
CSuspension
DColloid
Q2. The saline drip used in hospitals has concentration:
A5% m/v
B0.9% m/v
C10% m/m
D1% v/v
Q3. Who developed ORS, saving millions of lives?
AJohn Tyndall
BDilip Mahalanabis
CRobert Hooke
DC.V. Raman
📋 Answer Key
Q1A — Solute. Sugar gets dissolved, so it’s the solute; water (which dissolves) is the solvent.
Q2B — 0.9% m/v. This is the standard concentration of saline solution, safe for the body.
Q3B — Dilip Mahalanabis. Indian paediatrician who formulated ORS, popularised globally by WHO.

🌡️ 5.2.3 Solubility of Substances

📖 Definitions

Solubility — The maximum amount of solute that dissolves in a fixed quantity (100g or 100mL) of solvent at a given temperature.

Saturated Solution — A solution that cannot dissolve any more solute at that temperature.

🎯 Exam Point

• Solid solute in liquid solvent → solubility generally increases with temperature
• Gas in liquid solvent → solubility generally decreases with temperature

Solubility Curve

A graph of solubility (g per 100g water) vs temperature (°C) is called a solubility curve. Used to compare how different compounds dissolve at different temperatures.

💎 5.3.1 Crystallization

📖 Definitions

Crystal — A solid made up of particles arranged in a regular geometric pattern.

Crystallization — The process of forming crystals from a saturated solution. Used to separate two solids (one in small quantity, both soluble in same solvent) and for purification of solids.

If a saturated solution is cooled, the excess solute that can no longer stay dissolved separates out as crystals (since solubility decreases at lower temperature).

Examples in everyday life: rock salt crystals, sugar/candy crystals (mishri), snowflakes (water vapour freezing), frost on windows.

⭐ Principle

Purification by crystallization is based on the differences in solubility of a substance at different temperatures.

🧪 Activity 5.3 — Preparing Copper Sulfate Crystals
Step 1

Take copper sulfate + water, add dilute sulfuric acid (prevents unwanted reactions). Heat gently.

Step 2

Add more copper sulfate until saturated.

Step 3

Filter hot solution to remove insoluble impurities.

Step 4

Cool slowly without disturbing → large, shiny, well-shaped blue crystals form.

Step 5

Filter crystals, rinse with cold water, dry.

🎯 Exam Point — Cooling Rate Matters!

Slow cooling → larger, well-shaped crystals (more time for particles to arrange). Rapid cooling (e.g., ice-cold water) → smaller, less well-formed crystals.

🇮🇳 India’s Scientific Contributions — Salt Crystallization

Crystallization of salt was an ancient process used by coastal communities in India. Panga salt was obtained by boiling concentrated sea brines. Karkatch salt was produced by evaporation of seawater. These methods produced salt crystals of different sizes.

💡 Ready to Go Beyond — Natural Crystals

Large crystal deposits occur naturally in mines, caves, and Earth’s crust. Example: Mawsmai Cave in Sohra (Cherrapunji) and Quartz crystals.

✅ Check Your Understanding — Solubility & Crystallization
Q4. Solubility of a solid solute in a liquid generally _____ with temperature:
AIncreases
BDecreases
CStays the same
DBecomes zero
Q5. Slow cooling of a saturated solution produces:
ALarger, well-formed crystals
BSmaller, poorly-formed crystals
CNo crystals at all
DLiquid only
📋 Answer Key
Q4A — Increases. More heat energy allows more solid solute particles to dissolve in the solvent.
Q5A — Larger, well-formed crystals. Slow cooling gives particles time to arrange in regular geometric patterns.

🔥 5.3.2 Distillation

📖 Definition

Distillation — Separating two miscible liquids by heating until the liquid with lower boiling point vaporises; vapour is then cooled back to liquid. Used when boiling points differ by at least ~25°C.

Vapours pass through a condenser (cooled by circulating water) and condense as pure liquid, collected in a separate vessel. The other component remains in the distillation flask.

Example: Acetone (boils at 56°C) and water (boils at 100°C) — large difference allows clean separation by distillation.

🇮🇳 India’s Scientific Contributions — Mitti ka Ittar

In Kannauj, Uttar Pradesh (the perfume capital of India), the earthy smell after first rain is captured using the traditional Deg-Bhapka method of distillation, passed down through generations, to make a natural perfume called Mitti ka Ittar. The Fragrance and Flavour Development Centre, Kannauj supports this craft and trains farmers/entrepreneurs.

🔩 Ready to Go Beyond — Fractional Distillation & Petroleum Refinery

Fractional distillation separates mixture components with small differences (less than 25°C) in boiling points. Used in petroleum refineries to separate crude oil into: petroleum gas, petrol, kerosene (aviation fuel), diesel, lubricating oil, bitumen. The gas fraction is liquefied as LPG.

✅ Check Your Understanding — Distillation
Q6. Distillation is effective when boiling points of two liquids differ by at least:
A5°C
B10°C
C25°C
D50°C
Q7. Fractional distillation is used to separate liquids with boiling point differences:
ALess than 25°C
BMore than 100°C
CExactly 50°C
DCannot be specified
📋 Answer Key
Q6C — 25°C. Simple distillation requires this minimum boiling point difference for effective separation.
Q7A — Less than 25°C. Fractional distillation handles smaller boiling point differences, like in petroleum refining.

🎨 5.3.3 Paper Chromatography

📖 Definition

Paper Chromatography — A method of separating components of a mixture using differences in their interactions with the solvent and the paper. The liquid carries substances up the paper, separating them based on how fast they move.

🧪 Activity 5.5 — Separating Ink Colours
Setup

Draw a pencil line 2cm from bottom of chromatographic paper strip. Mark ink spot at centre.

Dipping

Place paper vertically in container with thin water layer; water level BELOW the spot.

Observation

As water rises, ink separates into different colour spots.

Conclusion

Black ink is actually a mixture of multiple dyes separated by chromatography.

🔩 Threads of Curiosity — Word Origin

‘Chromatography’ comes from Greek: chroma = “colour” + graphein = “to write” → literally “writing with colour”, because it was first used to separate coloured dyes and inks.

Used to separate pigments in spinach leaf extract, flower petal pigments, etc. Water doesn’t work as solvent in every case — sometimes alcohol or a mixture of solvents is needed.

✅ Check Your Understanding — Chromatography
Q8. The word ‘chromatography’ literally means:
AHeating with fire
BWriting with colour
CMixing liquids
DCooling vapours
Q9. In paper chromatography, the water level should initially be:
AAbove the ink spot
BBelow the ink spot
CExactly at the spot
DDoesn’t matter
📋 Answer Key
Q8B — Writing with colour. From Greek chroma (colour) + graphein (to write).
Q9B — Below the ink spot. If water touches the spot directly, the ink would dissolve into the water container instead of rising up the paper.

🔑 Keywords — Part 1

Homogeneous MixtureHeterogeneous MixtureSolutionSoluteSolventConcentrationMass by Mass %Mass by Volume %Volume by Volume %SolubilitySaturated SolutionSolubility CurveCrystalCrystallizationDistillationCondenserFractional DistillationPaper ChromatographyORSSaline SolutionPetroleum RefineryLPG

📖 Important Definitions — Part 1

Homogeneous MixtureA mixture with uniform composition throughout. Also called a solution. Example: sugar dissolved in water.
Heterogeneous MixtureA mixture that is NOT uniform — components are visible and may separate or settle over time.
SoluteThe substance that gets dissolved in a solution.
SolventThe substance that dissolves the solute to form a solution.
ConcentrationThe amount of solute dissolved in a given amount of solvent or solution.
SolubilityThe maximum amount of solute that dissolves in a fixed quantity of solvent (100g or 100mL) at a given temperature.
Saturated SolutionA solution that cannot dissolve any more solute at a given temperature.
CrystallizationThe process of forming pure solid crystals from a saturated solution, used for separation and purification of solids.
DistillationA method of separating miscible liquids by heating until the lower-boiling liquid vaporises, then condensing the vapour back to liquid.
Fractional DistillationProcess of separating components of a mixture with small differences (less than 25°C) in boiling points, used in petroleum refining.
Paper ChromatographyA technique to separate mixture components using differences in their interactions with solvent and paper, based on speed of movement.

❓ Frequently Asked Exam Concepts — Part 1

Why is exact proportion important when preparing solutions like ORS or pesticides? ▶
Each solution is designed to work optimally at a specific concentration. For ORS, the exact salt-sugar-water ratio ensures safe and effective rehydration — too concentrated could be harmful, too dilute won’t work. For pesticides, too little won’t protect crops effectively, while too much can damage crops, soil, and the environment, and may even be toxic. The right proportion balances effectiveness and safety.
Why does cooling rate affect crystal size and quality? ▶
Crystal formation requires particles to arrange themselves into a regular geometric pattern. When cooling is slow, particles have more time to find their correct positions in the growing crystal lattice, resulting in larger, well-formed crystals. Rapid cooling forces many small crystal nuclei to form simultaneously without enough time for proper arrangement, resulting in many small, poorly-formed crystals.
Why can’t distillation separate acetone and water if their boiling points were too close? ▶
Distillation works because as the mixture is heated, the liquid with the lower boiling point vaporises first and in much larger amounts. If two boiling points are too close (less than about 25°C apart), both liquids start vaporising in significant amounts at similar temperatures, leading to a mixed vapour rather than a pure single-component vapour. This makes clean separation by simple distillation difficult — fractional distillation (with repeated vaporisation-condensation cycles) is needed instead, as used in petroleum refining.
Why does the water level need to be below the ink spot in paper chromatography? ▶
If the water level were above or at the spot, the ink would directly dissolve into the bulk water in the container rather than being carried up the paper by capillary action. By keeping the water level below the spot, the water rises up through the paper via capillary action, passing through the ink spot and carrying the different coloured components upward at different rates based on their interaction with the paper and solvent — this is what causes the separation into distinct colour bands.

📌 Continue to Part 2 →

Separation of Heterogeneous Mixtures (Immiscible Liquids, Sublimation) · Suspensions · Centrifugation · Coagulation · Colloids · Tyndall Effect · Final Quiz