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Class 9 Science · Chapter 5 · Part 2 of 2

Exploring Mixtures and their Separation

Heterogeneous Mixtures · Suspensions · Centrifugation · Coagulation · Colloids · Tyndall Effect

💧 Immiscible Liquids
❄️ Sublimation
🌀 Centrifugation
🥛 Colloids
✨ Tyndall Effect

⬅️ Part 1 covered: Solutions & Homogeneous Separation

Classifying Mixtures, Solutions, Concentration, Solubility, Crystallization, Distillation, Chromatography

PART 2
This part covers: Separating Heterogeneous Mixtures → Immiscible Liquids → Sublimation → Suspensions → Centrifugation → Coagulation → Colloids → Tyndall Effect → Final Quiz.
📌 Jump to Section
Immiscible Liquids
Sublimation
Suspensions
Centrifugation
Coagulation
Colloids
Tyndall Effect
Summary
Definitions
Exam FAQs
Final Quiz

💧 5.4.1 Separation of Two Immiscible Liquids

📖 Definition

Immiscible Liquids — Liquids that do NOT mix and form separate layers, e.g., oil and water. Sand-water and iron filings-sulfur are other heterogeneous mixture examples.

🧪 Activity 5.6 — Separating Mustard Oil from Water
Setup

Pour 5mL mustard oil + 20mL water into a 50mL separating funnel.

Observation

Two layers form: oil (yellow, upper) and water (lower), since oil is less dense.

Procedure

Open stopcock slowly, collect water (lower layer) first. Close before oil reaches. Discard mixed portion. Collect oil separately.

Principle

Separation based on different densities of the two immiscible liquids.

⭐ Gas Mixtures

Gas particles move freely in all directions and mix easily/uniformly → most gas mixtures are homogeneous (e.g., hydrogen + oxygen used as rocket fuel). However, smoke (solid particles in air), fog (liquid droplets in air), and dust in air are heterogeneous mixtures with gas as one component.

❄️ 5.4.2 Sublimation

📖 Definitions

Sublimation — Direct change from solid state to vapour state (below its melting point) without passing through the liquid state.

Deposition — The reverse: vapour cooling directly back into solid without becoming liquid.

🧪 Activity 5.7 — Separating Camphor from Sand
Setup

Crushed camphor + sand mixture in china dish. Inverted funnel (nozzle plugged with cotton) over it.

Heating

Heat the china dish gently.

Observation

White solid camphor deposits on the inner wall of the funnel. Sand remains in the dish (sand doesn’t sublime).

Conclusion

Camphor sublimes (solid → vapour), then deposits back as solid on the cool funnel wall.

🔩 Examples of Sublimable Substances

Camphor, naphthalene (mothballs), and dry ice (solid CO₂, used for ice cream storage) all undergo sublimation.

Alloys — Mixing Metals

📖 Definition

Alloy — A homogeneous mixture of two or more metals, or a metal and non-metal. Metals don’t dissolve in each other at room temperature, but when melted together at high temperatures and cooled, they form an alloy. Physical methods CANNOT separate alloy components.

Alloy	Composition
Brass	~80% Copper + 20% Zinc
Bronze	~80% Copper + 20% Tin
Stainless Steel	Iron + Carbon (0.03-0.8%) + Chromium (16-18%) + Nickel (10-14%) + Molybdenum (2-3%)

✅ Check Your Understanding — Immiscible Liquids & Sublimation
Q1. Two immiscible liquids are separated using a:
ADistillation flask
BSeparating funnel
CChina dish
DTest tube
Q2. Sublimation is the change from:
ASolid directly to vapour
BLiquid to gas
CSolid to liquid
DGas to liquid
Q3. Which CANNOT be separated by physical methods?
ASand and water
BOil and water
CAlloy (e.g., brass)
DCamphor and sand
📋 Answer Key
Q1B — Separating funnel. Uses the stopcock to drain the denser lower layer first, based on density difference.
Q2A — Solid directly to vapour. Sublimation skips the liquid state entirely, occurring below the melting point.
Q3C — Alloy. Alloys are homogeneous mixtures of metals that cannot be separated by physical methods, unlike the other mixtures.

🌫️ 5.4.3 Suspensions

📖 Definition

Suspension — A heterogeneous mixture in which solid particles do NOT dissolve but remain suspended throughout the medium. Particles are visible to naked eye and larger than solution particles. Examples: sawdust in water, tea leaves in water, muddy water.

🎯 Exam Point — Cleaning Muddy Water

Filtration alone is NOT always sufficient (tiny particles pass through and water stays cloudy). We then use centrifugation and/or coagulation.

🌀 A. Centrifugation

📖 Definition

Centrifugation — A process of spinning a mixture in a tube at high speed. Centrifugal force (outward force on a body in circular motion) causes heavier particles to move outwards and settle at the bottom, while lighter liquid stays at the top.

Widely used in laboratories to separate blood components (RBCs, plasma) and in chemical industries.

🔩 Threads of Curiosity — Folk Dance Connection

The “spinning game” (used to explain centrifugal force) is a folk dance called phugadi in Marathi and kikli in Punjabi.

🌏 Bridging Science and Society — The Paperfuge

A simple hand-powered device called a paperfuge (using a cardboard disc and string) performs centrifugation WITHOUT electricity. By spinning blood samples at high speed, it separates components like a lab centrifuge. This low-cost tool helps detect diseases like malaria and anaemia in remote areas with limited access to medical equipment.

🌏 Bridging Science and Society — Donate Blood

Donated blood is tested, and once blood group is identified, it’s separated into components: plasma, platelets, white and red blood cells via centrifugation. These are stored in blood banks. The body naturally replaces donated blood within a few weeks, making donation safe.

🧊 B. Coagulation

📖 Definitions

Coagulation — Process where a substance (coagulant) causes fine suspended particles to clump together, forming larger clumps that settle by gravity (sedimentation), then separated by decantation or filtration.

Coagulant — A substance that causes coagulation, e.g., alum (fitkari).

Steps: Add powdered alum to muddy water → alum coagulates suspended impurities into clumps → clumps settle (sedimentation) → separate by decantation/filtration.

Everyday example: Formation of cheese (paneer) from milk uses coagulation — acid (lemon juice or vinegar) acts as the coagulant, causing milk proteins to clump together.

✅ Check Your Understanding — Suspensions, Centrifugation & Coagulation
Q4. Particles in a suspension are:
AVisible to the naked eye
BInvisible
CLess than 1nm
DGas particles
Q5. Centrifugation separates particles based on differences in:
AColour
BMass/density (heavier vs lighter particles)
CBoiling point
DMelting point
Q6. Which substance is commonly used as a coagulant?
AAlum (fitkari)
BCommon salt
CSugar
DChalk powder
📋 Answer Key
Q4A — Visible to naked eye. Suspension particles are larger (more than 1000nm) and clearly visible, unlike solution particles.
Q5B — Mass/density. Heavier particles experience more centrifugal force and move outward/settle faster.
Q6A — Alum. Alum is the classic coagulant used to clump fine suspended impurities in water purification.

🥛 5.4.4 Colloids

📖 Definition

Colloid — Neither a true solution nor a true suspension. Components don’t settle over time (like solutions) but particles are larger than solution particles. Examples: blood, milk, tomato sauce, ice cream.

Solutions vs Suspensions vs Colloids — Particle Size

💧
Solution
< 1 nm
Smallest particles. Cannot be seen, don’t settle, no Tyndall effect, can’t be filtered.
🥛
Colloid
1 – 1000 nm
Medium particles. Don’t settle, particles dispersed uniformly, shows Tyndall effect, can’t be filtered (usually).
🟤
Suspension
> 1000 nm
Largest particles. Visible to naked eye, settles over time, shows Tyndall effect, separable by filtration.
⭐ Components of a Colloid

• Dispersed phase — The solute-like component (dispersed particles)
• Dispersion medium — The component in which the dispersed phase is suspended

Emulsions — A Special Type of Colloid

💡 Threads of Curiosity — Emulsions

Emulsion — A colloid where both dispersed phase and dispersion medium are liquids.

• Oil-in-water emulsion — Example: milk, vanishing creams
• Water-in-oil emulsion — Example: butter, body lotions, cold cream

Emulsifying agents stabilise emulsions (e.g., proteins in milk and butter). Some medicines are prepared as emulsions to disperse easily in water and reduce greasy feel.

✅ Check Your Understanding — Colloids
Q7. The particle size range for a colloid is:
ALess than 1 nm
B1 to 1000 nm
CMore than 1000 nm
DExactly 1 nm
Q8. Milk is an example of a:
AOil-in-water emulsion
BWater-in-oil emulsion
CBoth A is correct
DTrue solution
📋 Answer Key
Q7B — 1 to 1000 nm. Colloid particle size falls between solutions (<1nm) and suspensions (>1000nm).
Q8A — Oil-in-water emulsion. Milk has tiny fat droplets dispersed in water, with proteins acting as emulsifying agents.

✨ 5.5 Tyndall Effect

📖 Definition

Tyndall Effect — The scattering of light by particles in a colloid or suspension. Named after scientist John Tyndall, who first explained it.

From Activity 5.1:

• Solution A (salt water) — light path NOT visible (no scattering)
• Suspension B (chalk-water) — light path IS visible (scattered)
• Colloid C (milk-water) — light path IS visible (scattered), even though it looks homogeneous!

🎯 Exam Point

Scattering occurs when light passes through a colloid or suspension but NOT through a transparent solution (true solution particles are too small to scatter light).

⭐ Everyday Examples of Tyndall Effect

• A beam of light through a small hole in a dark room (scattered by dust/smoke particles)
• Floodlights in a sports stadium at night (visible beams)
• Sunlight through gaps in tree leaves (visible rays)

Complete Comparison — Solution vs Suspension vs Colloid

Property	Solution	Suspension	Colloid
Nature	Homogeneous	Heterogeneous	Looks homogeneous
Particle size	<1 nm	>1000 nm	1-1000 nm
Visibility	Not visible	Visible to naked eye	Not visible to naked eye
Filtration	Cannot separate	Can separate	Cannot separate (usually)
Settling	Does not settle	Settles over time	Does not settle
Tyndall effect	Does NOT show	Shows	Shows

✅ Check Your Understanding — Tyndall Effect
Q9. The Tyndall effect is named after:
ARobert Hooke
BJohn Tyndall
CIsaac Newton
DAlbert Einstein
Q10. Which does NOT show the Tyndall effect?
ATrue solution (e.g., salt water)
BMilk
CMuddy water (suspension)
DSmoke in air
📋 Answer Key
Q9B — John Tyndall. He first explained the scattering of light by particles in colloids/suspensions.
Q10A — True solution. Solution particles (<1nm) are too small to scatter visible light, so no Tyndall effect is seen.

📋 Chapter Summary — Full Chapter

🧪MixturesHomogeneous (uniform, solution) vs Heterogeneous (non-uniform, visible particles).
📊Concentration% m/m (mass-mass), % m/v (mass-volume), % v/v (volume-volume).
💎CrystallizationPure solid from saturated solution. Slow cooling = bigger crystals.
🔥DistillationMiscible liquids, boiling point diff ≥25°C. Fractional: <25°C diff (petroleum).
🎨ChromatographySeparates by different movement rates on paper using solvent.
💧Immiscible LiquidsSeparating funnel, based on density difference.
❄️SublimationSolid→vapour directly. Camphor, naphthalene, dry ice.
🌀CentrifugationHigh-speed spinning separates by density (heavier outward/down).
🧊CoagulationCoagulant (alum) clumps fine particles → settle → filter.
🥛Colloids1-1000nm, don’t settle, shows Tyndall effect. Blood, milk, ice cream.
✨Tyndall EffectLight scattering by colloid/suspension particles. NOT in true solutions.

🔑 Keywords — Part 2

Immiscible LiquidsSeparating FunnelSublimationDepositionAlloyBrassBronzeStainless SteelSuspensionCentrifugationCentrifugal ForcePaperfugeCoagulationCoagulantSedimentationDecantationColloidDispersed PhaseDispersion MediumEmulsionEmulsifying AgentTyndall EffectJohn TyndallBlood Transfusion

📖 Important Definitions — Part 2

Immiscible LiquidsLiquids that do not mix and form separate layers, such as oil and water.
SublimationThe transition of a solid directly into vapour, below its melting point, without passing through the liquid state.
AlloyA homogeneous mixture of two or more metals, or a metal and non-metal, that cannot be separated by physical methods.
SuspensionA heterogeneous mixture in which solid particles do not dissolve but remain suspended; particles are visible and settle over time.
CentrifugationA process of spinning a mixture at high speed, using centrifugal force to separate heavier particles from lighter liquid.
CoagulationThe process of adding a coagulant to make fine suspended particles clump together and settle by gravity.
ColloidA mixture with particle size between 1-1000 nm, intermediate between solution and suspension; doesn’t settle but shows the Tyndall effect.
EmulsionA colloid where both dispersed phase and dispersion medium are liquids, e.g., milk (oil-in-water) or butter (water-in-oil).
Tyndall EffectThe scattering of light by particles present in a colloid or suspension, making the light’s path visible.

❓ Frequently Asked Exam Concepts — Part 2

Why doesn’t a true solution show the Tyndall effect? ▶
In a true solution, the solute particles are extremely small (less than 1 nanometre in diameter) — smaller than the wavelength of visible light. These tiny particles cannot effectively scatter light waves, so the light passes straight through without any visible scattering. In contrast, colloids (1-1000 nm) and suspensions (greater than 1000 nm) have particles large enough to interact with and scatter light, making the light’s path visible (the Tyndall effect).
Why is blood considered a colloid and not a true suspension? ▶
In a true suspension, particles are large enough to settle out over time when left undisturbed. Blood cells, however, remain uniformly dispersed throughout the blood plasma and do NOT settle naturally over time (they only separate when subjected to centrifugation, an external force). This behavior — particles dispersed evenly without natural settling, combined with particle sizes in the colloidal range — classifies blood as a colloid, not a suspension.
Why can’t alloys be separated by physical methods like filtration or distillation? ▶
Alloys are formed when metals are melted together at high temperatures and then cooled, creating a homogeneous mixture where the different metal atoms are intimately mixed at the atomic/molecular level, similar to how solute and solvent particles mix in a solution. Unlike a mixture of solid sand and salt (which can be separated by dissolving one component), the metal atoms in an alloy don’t have a simple physical or chemical handle (like differential solubility, boiling point, or density at the macroscale) that allows physical separation. Special chemical or metallurgical processes (not basic physical separation techniques) are needed to separate alloy components.
Why is filtration sometimes insufficient to clean muddy water completely? ▶
Filter paper or cloth has pores of a certain size. Larger mud particles get trapped by the filter, but very fine suspended particles (colloidal-sized or very small suspension particles) can pass right through these pores along with the water, leaving the filtrate still cloudy. This is why additional techniques like coagulation (using alum to clump fine particles into larger masses that CAN be filtered or settled) or centrifugation (using force to separate even very fine particles) are needed for complete purification.

🏆 Final Practice Quiz
15 Mixed MCQs · Full Chapter Coverage (Part 1 + Part 2)
Q1 — Sugar dissolved in water forms a:
AHomogeneous mixture
BHeterogeneous mixture
CSuspension
DColloid
Q2 — If 15g salt dissolved in 85g water (total 100g), the % m/m is:
A15% m/m
B85% m/m
C100% m/m
D50% m/m
Q3 — Solubility of a gas in liquid generally _____ with increasing temperature:
AIncreases
BDecreases
CStays constant
DBecomes infinite
Q4 — Which technique separates copper sulfate crystals from solution?
ACrystallization
BSublimation
CCentrifugation
DCoagulation
Q5 — Acetone (boils at 56°C) and water (boils at 100°C) are best separated by:
ADistillation
BFiltration
CSublimation
DChromatography
Q6 — Black ink separates into multiple colours via:
ADistillation
BPaper chromatography
CCrystallization
DSublimation
Q7 — Oil and water are separated using a:
AChina dish
BSeparating funnel
CCondenser
DWatch glass
Q8 — Camphor and sand are separated by:
ASublimation
BDistillation
CCentrifugation
DCoagulation
Q9 — Brass (Cu+Zn) is an example of an alloy that CANNOT be separated by:
APhysical methods
BHeating to high temperature only
CCooling
DMelting
Q10 — Components of blood are separated in labs using:
ACentrifugation
BDistillation
CSublimation
DChromatography
Q11 — Muddy water is purified using alum, which acts as a:
ACoagulant
BSolvent
CCatalyst
DEmulsifier
Q12 — Particle size of a colloid lies between:
A1-1000 nm
B0-1 nm
C2000-3000 nm
DGreater than 5000 nm
Q13 — Which mixture does NOT show the Tyndall effect?
ASugar solution
BMilk
CMuddy water
DFog
Q14 — Butter is an example of a:
AOil-in-water emulsion
BWater-in-oil emulsion
CTrue solution
DSuspension
Q15 — Paneer (cheese) formation from milk uses coagulation with:
AAcid (lemon juice/vinegar)
BAlum
CBase
DSalt
Your Final Quiz Score
0/15
📋 Final Quiz — Answer Key with Explanations
Q1A — Homogeneous. Sugar-water has uniform composition throughout, equally sweet at every sip.
Q2A — 15% m/m. (15÷100)×100 = 15% m/m.
Q3B — Decreases. Unlike solids, gas solubility in liquids decreases as temperature rises (e.g., warm soda goes flat faster).
Q4A — Crystallization. Forms pure solid crystals from a saturated solution.
Q5A — Distillation. Boiling point difference of 44°C (well above the 25°C threshold) allows clean separation.
Q6B — Paper chromatography. Separates dye components based on differing rates of movement on paper.
Q7B — Separating funnel. Uses density difference and a stopcock to drain layers separately.
Q8A — Sublimation. Camphor sublimes and deposits elsewhere; sand remains behind (doesn’t sublime).
Q9A — Physical methods. Alloys are homogeneous metal mixtures that require chemical/metallurgical methods, not basic physical separation.
Q10A — Centrifugation. High-speed spinning separates plasma, RBCs, WBCs, platelets by density.
Q11A — Coagulant. Alum causes fine suspended impurities to clump together for easier removal.
Q12A — 1-1000 nm. This is the defined particle size range for colloids, between solutions and suspensions.
Q13A — Sugar solution. True solutions have particles too small to scatter light; milk, muddy water, and fog all show the Tyndall effect.
Q14B — Water-in-oil. In butter, tiny water droplets are dispersed in a continuous oil/fat medium.
Q15A — Acid. Lemon juice or vinegar (acid) coagulates milk proteins to form paneer/cheese.