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NCERT Class 9 Science Chapter 5 question answers for Exploring Mixtures and their Separation (CBSE 2026-27), with every Think It Over, Activity, Pause & Ponder, Worked Example, Revise Reflect Refine and Journey Beyond question solved step by step. Use it alongside your Class 9 Science chapter 5 notes to check each answer and numerical.
This chapter returns to chemistry and sorts every mixture you meet into true solutions, colloids and suspensions, then builds the toolkit for separating them. These Class 9 Science Chapter 5 Exploring Mixtures and their Separation NCERT solutions cover the Tyndall effect, % m/m, % m/v and % v/v concentration numericals, solubility curves, chromatography, distillation and the separating funnel, with every numerical worked step by step.
Last updated 20 October 2026 · Reviewed by Suchita Arora, 13+ years teaching CBSE Maths & Science
Exploring Mixtures and their Separation classifies mixtures — solutions, suspensions and colloids — by particle size and behaviour, including the Tyndall effect that tells them apart. It shows how to express concentration (% m/m, % m/v, % v/v), how solubility changes with temperature and drives crystallisation, and the full toolkit of separation techniques: evaporation, distillation, paper chromatography, the separating funnel, sublimation and centrifugation. Every question is solved here, section by section, as complete Class 9 Science Chapter 5 NCERT solutions with answers.
Particle size, settling behaviour, and the Tyndall effect — why milk scatters light but salt water doesn't.
% m/m, % m/v and % v/v calculations, plus how solubility curves predict how much solid crystallizes on cooling.
Choosing the right method — distillation, chromatography, sublimation, or centrifugation — based on what the mixture actually is.
Types of mixtures
| Property | Solution | Colloid | Suspension |
|---|---|---|---|
| Particle size | < 1 nm | 1 – 1000 nm | > 1000 nm |
| Appearance | Clear, transparent | Often clear or translucent | Opaque, cloudy |
| Settling | No | No | Yes (over time) |
| Tyndall effect | No | Yes | Yes |
| Filtration | Passes through | Passes through | Retained by filter |
| Examples | Salt/water, brass | Milk, blood, fog | Sand/water, muddy water |
Key formulae
Separation methods summary
| Method | Type of mixture | Principle | Example |
|---|---|---|---|
| Crystallization | Homogeneous (solid in liquid) | Solubility decreases on cooling | CuSO₄ from water, salt from brine |
| Distillation | Miscible liquids or liquid + solid | Difference in boiling points (≥25°C) | Acetone-water, water from salt |
| Paper chromatography | Homogeneous (mixed dyes etc.) | Different rates of movement in solvent | Ink dyes, flower pigments |
| Separating funnel | Immiscible liquids | Difference in density | Oil and water, mustard oil |
| Sublimation | Solid + non-sublimable solid | One solid sublimes, the other doesn't | Camphor + sand, naphthalene + salt |
| Centrifugation | Suspension/colloid | Centrifugal force separates by density | Blood components, clay from water |
| Coagulation | Suspension (fine particles) | Coagulant makes particles clump | Alum + muddy water, cheese making |
Muddy water is a suspension. Its particles are very large (more than 1000 nm) and heavy.
Gravity pulls these large particles down, so they settle at the bottom with time.
Milk is a colloid. Its particles are much smaller (1 – 1000 nm) and are spread evenly through the liquid.
These small particles do not settle over time.
| Evaporation | Boiling |
|---|---|
| Takes place at any temperature | Takes place only at the boiling point |
| Takes place only at the surface of the liquid | Takes place throughout the liquid |
| Slow process. No bubbles are formed | Fast process. Bubbles are formed |
| Causes cooling of the remaining liquid | Heat has to be supplied continuously |
The air contains tiny particles of dust, smoke and water droplets.
When sunlight passes through the small gaps, these particles scatter (spread) the light in all directions.
The scattered light enters our eyes, so the path of the light beam becomes visible as bright rays.
This scattering of light by particles is the Tyndall effect.
| Step | A: salt + water | B: chalk + water | C: milk + water |
|---|---|---|---|
| 4. Particles visible? | No. Clear and transparent | Yes. Cloudy, particles can be seen | No. Looks uniform (milky) |
| 5. Laser beam | Path of the beam is not visible | Path of the beam is visible | Path of the beam is visible |
| 6. On standing | Nothing settles | Chalk particles settle at the bottom | Nothing settles |
| 7. Filtration | No residue on the filter paper | White residue on the filter paper | No residue. Milk passes through |
Step 8: the three mixtures are different types of mixtures.
A is a true solution, B is a suspension and C is a colloid.
Prediction: the curve of B lies far above the curve of A at every temperature. So compound B dissolves more than A in a given amount of water at any given temperature.
A at 20 °C is about 34 g and at 60 °C is about 52 g per 100 g of water.
B at 20 °C is about 208 g and at 60 °C is 287 g per 100 g of water.
From 20 °C to 60 °C, the solubility of B rises by about 79 g, while that of A rises by only about 18 g.
Observations:
1. Copper sulfate dissolves in hot water to give a blue solution. More is added until it is saturated.
2. Filtering the hot solution removes the insoluble impurities.
3. On slow cooling, shiny, blue, well-shaped crystals of copper sulfate separate out.
Why is the solution cooled slowly? Slow cooling gives the particles enough time to come together and arrange in a regular pattern. So larger, well-shaped crystals are formed.
Why are the crystals rinsed with cold water? Cold water removes the impurities sticking to them and dissolves very little of the crystals.
You may also try: on the glass plate, the water evaporates quickly and small, tiny crystals are seen.
This is not a good way to get large, well-shaped crystals, because quick evaporation does not give the particles time to arrange. It is useful only for a quick look.
Step 1: Seawater is let into large, shallow pans (salt pans).
Step 2: The heat of the Sun and the wind make the water evaporate slowly. The solution becomes more and more concentrated.
Step 3: When the solution becomes saturated, the salt starts separating out.
Step 4: Crystals of salt are formed. They are collected, washed and dried.
The process is crystallization, and it works because water evaporates but salt does not.
Step 5: the water rises slowly up the paper and carries the ink with it.
Step 6: the black spot spreads and splits into different coloured spots (for example blue, pink and yellow) at different heights.
Inference: black ink is not a single colour. It is a mixture of different dyes.
The dyes separate because they move up the paper at different speeds, depending on how they interact with the paper and the water.
The water level must be below the spot at the start. Otherwise, the ink would dissolve in the water.
Step 2: the oil and water do not mix. They form two separate layers.
Step 3 (why the oil is on top): the two liquids are immiscible. Mustard oil is less dense than water, so it floats on water as the upper layer.
Steps 4 to 7: the water (lower layer) is drained slowly through the stopcock. The stopcock is closed just before the oil reaches it. The small middle portion with both liquids is discarded. The oil is then collected separately.
Step 6: yes, white solid deposits are seen on the cooler inner wall of the funnel.
Step 7: the white deposit is camphor. The sand stays in the china dish.
Explanation: on heating, camphor changes directly from solid to vapour without becoming a liquid. This is sublimation.
The vapour touches the cool wall of the funnel and changes back directly into a solid. This is deposition.
Sand does not sublime, so it remains in the dish. The cotton plug stops the vapour from escaping.
Making it: cut a disc of cardboard. Make two holes close to the centre and pass a thick thread through them. Tie the ends to make a loop on each side.
Using it: tape a small closed bottle or tube of the mixture on the disc. Hold the two loops and twist the disc by winding the thread. Then pull the thread apart and let go, so that the disc spins quickly.
Observation: the heavier particles are thrown outwards and settle at the outer end of the tube. The lighter liquid stays near the centre.
Mixture to separate: muddy water, or chalk powder in water. Each has heavy particles that settle faster on spinning.
This is the idea behind the centrifuge and the paperfuge, used to separate the parts of blood.
| S. No. | Property | Solution | Suspension | Colloid |
|---|---|---|---|---|
| 1. | Nature (homogeneous / heterogeneous) | Homogeneous | Heterogeneous | Heterogeneous (looks homogeneous) |
| 2. | Particle size | Less than 1 nm | More than 1000 nm | 1 – 1000 nm |
| 3. | Visibility | Particles cannot be seen | Particles are visible to the naked eye | Particles cannot be seen by the naked eye |
| 4. | Separation by filtration | Cannot be separated | Can be separated (residue is left) | Cannot be separated |
| 5. | Settling | Do not settle | Settle on standing | Do not settle |
| 6. | Tyndall effect | Not shown | Shown | Shown |
Given: concentration = 4 % m/m, mass of talcum powder = 300 g
To find: mass of zinc oxide
4 % m/m means 4 g of zinc oxide in every 100 g of the powder.
Given: 2 tablespoons of 15 mL each, volume of juice = 150 mL
To find: % v/v of the concentrate
Volume of concentrate (solute):
Volume of solution = 150 mL
5 % v/v means 5 mL of acetic acid in every 100 mL of vinegar.
Step 1: measure 5 mL of glacial acetic acid with a measuring cylinder (use gloves, and do it with an adult or the teacher, as it is strong and corrosive).
Step 2: pour some water into a larger measuring cylinder or flask.
Step 3: add the 5 mL acid to the water and stir.
Step 4: add more water to make the total volume 100 mL. So, about 95 mL of water is used.
For larger quantities, keep the same ratio. For example, 50 mL of acid is made up to 1 litre.
From the graph, the solubility of compound B falls from about 360 g to 287 g per 100 g of water between 80 °C and 60 °C. That is a fall of about 73 g.
The solubility of compound A falls from about 63 g to about 52 g. That is a fall of only about 11 g.
The more the solubility falls on cooling, the more solid is deposited.
Crystals form when the particles come together and arrange in a regular pattern.
Faster evaporation: the particles get less time to arrange. Many small crystals form quickly.
Slower evaporation: the particles get more time to join the growing crystals. Fewer, larger and better-shaped crystals form.
Evaporation removes the water and leaves the salt. Distillation can also recover water from the salt solution, leaving the salt in the flask.
Distillation separates liquids because their boiling points are different (by at least about 25 °C).
If the solvent is above the spot, the ink dissolves in the solvent and is not carried up the paper.
Evaporation removes the solvent completely, and the solid left can be impure. Crystallization forms pure crystals from a saturated solution on cooling, based on the change in solubility.
Immiscible liquids do not mix with each other.
They have different densities. The liquid with lower density floats on top, and the liquid with higher density stays at the bottom.
So the two liquids form two separate layers, and the lower layer can be drained through the stopcock.
| Sublimation | Evaporation |
|---|---|
| A solid changes directly into vapour | A liquid changes into vapour |
| The liquid state is not formed | The liquid state is present |
| Happens on heating, below the melting point of the solid | Happens at the surface, at any temperature below the boiling point |
| Example: camphor, naphthalene, dry ice | Example: water drying from wet clothes |
The water droplets or ice crystals are tiny. They are spread through the air and do not settle quickly.
Their size is between that of a solution and a suspension (1 – 1000 nm range for colloids).
They scatter the sunlight (Tyndall effect), which is why the beams of light are seen through clouds and why clouds look white.
Smoke and dust are tiny solid particles suspended in the air.
These particles scatter the light that passes through the air (Tyndall effect).
Because of the scattering, the light spreads in all directions, and distant objects look blurred and hazy.
Given: mass of salt (solute) = 10 g, mass of water (solvent) = 90 g
To find: mass by mass percentage
Total mass of solution = mass of solute + mass of solvent
Given: mass of glucose (solute) = 5 g, volume of solution = 100 mL
To find: mass by volume percentage
Given: volume of pesticide (solute) = 1 mL, total volume of solution = 100 mL
To find: volume by volume percentage
Oil and water do not mix. They form two separate layers, so the composition is not uniform.
Other heterogeneous mixtures: sand and water, iron filings and sulfur, muddy water, smoke, fog and dust in air, sawdust in water.
Too little pesticide: it may not protect the crops from pests.
Too much pesticide: it can damage the crops, the soil and the environment.
Other examples: ORS (oral rehydration solution), liquid medicines and syrups, saline (0.9 % m/v), fertiliser solutions, and even a cup of tea.
The solubility of a solid generally falls when the temperature falls. So the solution can no longer hold all the dissolved solute.
Example: a saturated solution of B at 60 °C has 287 g of B in 100 g of water. At 40 °C only 241 g can stay dissolved.
The rest separates out as a pure solid, often as crystals:
In evaporation, the liquid that evaporates is lost to the air, so only the liquid that does not evaporate is left in the container.
For the mixture of acetone and water, if we heat the mixture, the acetone evaporates more easily (boiling point 56 °C) and escapes into air. We cannot get both liquids back.
Method: distillation. The liquid with the lower boiling point vaporises first. Its vapour is cooled in a condenser and is collected as a liquid. The other liquid stays in the flask.
Gases mix easily with other gases, so most gas mixtures are homogeneous.
Heterogeneous mixtures with a gas as one component: smoke (solid particles in air), fog (water droplets in air), dust in air, and clouds.
Layers form because one liquid is lighter than the other and floats on it.
If both liquids have the same density, neither of them floats on the other.
So no clear upper and lower layer will form. The liquids stay mixed as droplets and look cloudy.
The mixture cannot be separated by a separating funnel.
Sublimation can be used when one component sublimes on heating and the other does not.
Examples: ammonium chloride and common salt, naphthalene and sand (or salt), iodine and sand, camphor and salt.
Metals do not dissolve in each other at room temperature.
When metals are melted at a high temperature, they can be mixed to form a solution.
When the hot mixture cools, it solidifies into a new material that looks like a single metal. Such a homogeneous mixture is called an alloy.
Examples: brass (about 80% copper and 20% zinc), bronze (about 80% copper and 20% tin) and stainless steel.
Physical methods cannot separate the components of an alloy.
The heavier mud settles at the bottom, but the water may still look cloudy. Filtration alone does not remove the tiny particles.
Centrifugation: spin the muddy water at a high speed. The centrifugal force throws the heavier particles outwards to the bottom of the tube, and the clear liquid stays at the top.
Coagulation: add a little powdered alum (fitkari). It makes the fine particles clump together. The larger clumps settle down (sedimentation).
The clear water is then separated by decantation or filtration.
1. Making paneer (cheese) from milk. Lemon juice or vinegar coagulates the milk proteins.
2. Making curd from milk is also a thickening of milk proteins.
3. Clotting of blood at a cut.
4. Purifying water by alum, in water treatment plants.
5. Setting of rubber latex with acid.
Is it a suspension? A suspension has particles that are visible and settle on their own. Blood cells cannot be seen by the naked eye and do not settle on their own.
Is it a solution? A solution does not scatter light and cannot be separated by spinning. Blood can be separated by centrifugation, and its cells scatter light.
Blood is neither a solution nor a true suspension.
Hypothesis: rapid cooling gives smaller, less well-formed crystals than slow cooling.
Step 1: prepare a hot, saturated solution of copper sulfate (with a drop of dilute sulfuric acid, under adult supervision) and filter it.
Step 2: divide it into two equal parts in two identical beakers, A and B.
Step 3: keep beaker A in ice-cold water to cool it rapidly.
Step 4: keep beaker B at room temperature, covered and undisturbed, to cool it slowly.
Step 5: after the same time, filter the crystals from both, dry them and compare their size and shape with a magnifying glass.
Kept the same: amount and concentration of solution, type and size of beaker, starting temperature.
Changed: only the rate of cooling.
Expected result: beaker A gives small, poorly shaped crystals and beaker B gives larger, shiny, well-shaped crystals. This supports the hypothesis.
(i) wrong: smoke is solid particles in air. It is heterogeneous, not homogeneous.
(ii) wrong: brass is an alloy (homogeneous), vinegar is a solution (homogeneous) and muddy water is heterogeneous.
(iii) wrong: milk is a colloid, which is classed as heterogeneous.
(iv) correct: muddy water, milk and blood are heterogeneous, and brass is homogeneous.
The Tyndall effect is the scattering of light by particles. It happens in colloids and suspensions, but not in true solutions.
(a) Air and dust: dust particles are large enough to scatter light. Tyndall effect is shown.
(b) Copper sulfate and water: it is a true solution with very small particles. No scattering.
(c) Starch and water: starch forms a colloid with particles of 1 – 1000 nm. It scatters light.
(d) Acetone and water: it is a true solution. No scattering.
So (a) and (c) show the Tyndall effect. Options (i), (ii) and (iv) each include (b) or (d), which are solutions, so they are wrong.
| Solution | Suspension | Colloid | |
|---|---|---|---|
| Properties | Small-sized particles (less than 1 nm diameter) Particles remain evenly distributed Transparent Cannot be separated by filtration | Large-sized particles Settles down when left undisturbed (more than 1000 nm in diameter) Heterogeneous mixture Separates by filtration Scatters light | Moderate-sized particles (1 – 1000 nm) Particles remain evenly distributed Does not settle down Scatters light Cannot be separated by filtration |
| Examples | Salt solution Brass | Sand in water Mud | Milk Butter Smoke |
The ingredients are solids, so the mass by mass percentage (% m/m) is suitable.
Total mass of the mixture = 75 + 420 + 5 = 500 g
Sugar:
Flour:
Sodium hydrogencarbonate:
Check: 15 + 84 + 1 = 100%
Copper:
Zinc: the rest of the brass is zinc.
Density of oil:
Water has a density of 1 g/mL. Oil is less dense than water and does not mix with it (immiscible).
Yes, the oil will form a separate layer, and it will be on top.
Separation: use a separating funnel. Open the stopcock slowly to drain the lower layer (water). Close it before the oil reaches the stopcock. Collect the oil separately.
Assertion A: true. The particles of a solution are very small, so a solution does not scatter light and the beam is not visible.
Reason R: false. The particles in a solution are smaller than 1 nm, not larger than 100 nm. Larger particles would scatter light.
| Mixture | Method of separation | Reason for selection |
|---|---|---|
| Mud from muddy water | Sedimentation, decantation or filtration. Centrifugation or alum (coagulation) if it is still cloudy | Mud particles are large and heavy. They settle, or are removed by filtration |
| Plasma from other components in the blood sample | Centrifugation | Spinning throws the heavier blood cells outwards. The lighter plasma stays at the top |
| Naphthalene and sand | Sublimation | Naphthalene sublimes on heating, but sand does not |
| Chalk powder and common salt | Add water, then filter. Evaporate the filtrate | Salt dissolves in water but chalk does not. Chalk stays on the filter paper, and salt is got by evaporation |
| Common salt and water | Evaporation (or crystallization). Distillation, to also get the water | Water evaporates, but salt does not |
| Oil from water | Separating funnel | They are immiscible and have different densities |
| Pigments of the flower | Paper chromatography | The pigments move at different rates on the paper. A solvent such as alcohol may be needed |
The liquids are miscible, so they cannot be separated by a separating funnel or filtration.
The difference in their boiling points is:
This is more than 25 °C, so they can be separated by distillation.
Procedure:
1. Put the mixture in the distillation flask and heat it slowly.
2. The thermometer shows 60 °C when A vaporises first, because it has the lower boiling point.
3. The vapour of A passes through the water condenser, where it cools and changes back into a liquid.
4. Liquid A is collected in the conical flask.
5. Liquid B, with the higher boiling point, stays in the distillation flask.
| Evaporation | Crystallization | Distillation | |
|---|---|---|---|
| Principle | The liquid changes to vapour at the surface and the solid is left | The solubility of a solid falls on cooling a saturated solution, so crystals form | Liquids differ in boiling point. One vaporises first and is condensed |
| What is obtained | Solid (the solvent is lost) | Pure crystals of the solid | The liquid (solvent) and the solid or other liquid left behind |
| Preferred when | We want only the dissolved solid, and the solid does not break on heating (salt from sea water) | We want a pure solid, or the solid breaks on strong heating (copper sulfate crystals) | We want the liquid back, or to separate two miscible liquids (water from acetone) |
The particles of a suspension settle on standing. So the blood cells would settle down in the blood vessels.
They would not stay evenly spread, and the blood could not carry oxygen, nutrients and hormones to all parts of the body properly.
The cells would also block the narrow vessels.
The blood cells (red cells, white cells and platelets) are the dispersed particles.
The liquid in which they are spread is the plasma.
Step 1 (figure 1) – Sublimation: the mixture is heated in a china dish covered with an inverted funnel. Naphthalene sublimes and is deposited on the funnel. Sand and salt are left.
Step 2 (figure 3) – Filtration: the left-over mixture is stirred in water. The salt dissolves, but the sand does not. On filtering, the sand is left on the filter paper and the salt solution is the filtrate.
Step 3 (figure 2) – Evaporation: the filtrate is heated in a china dish. The water evaporates and the salt is left.
Sublimation has to be done first, because the other steps need water or heating of the salt solution.
Water and acetone are miscible, so they form a homogeneous mixture and cannot be separated by filtration or a separating funnel.
Their boiling points are very different: acetone boils at about 56 °C and water at 100 °C.
This is more than 25 °C. On heating, acetone vaporises first, before water vapour forms in a large amount.
The acetone vapour is cooled in the condenser and collected as pure liquid acetone. The water remains in the flask.
At 40 °C, 62 g of KNO₃ dissolves in 100 g of water.
For 50 g of water, the mass needed is half of this.
At 80 °C, 54 g of KCl dissolves in 100 g of water.
At 25 °C the solubility is about 36 g (between 35 g at 20 °C and 37.4 g at 30 °C).
About 18 g of KCl cannot stay dissolved in every 100 g of water. The solution turns cloudy and crystals of potassium chloride settle at the bottom as it cools.
The solubility of these solid salts increases as the temperature increases. The increase is different for different salts:
| Salt | 10 °C | 80 °C | Rise in solubility |
|---|---|---|---|
| Potassium nitrate | 21 | 167 | 146 g (very large) |
| Ammonium chloride | 24 | 66 | 42 g (large) |
| Potassium chloride | 35 | 54 | 19 g (small) |
| Sodium chloride | 36 | 37 | 1 g (almost no change) |
Mass of solution = mass of sugar + mass of water.
Concentration is the amount of solute in a given amount of solution.
Solution C has the highest percentage, 27.3%. It has the most sugar in every 100 g of solution.
The set-up has a flask, a condenser and a receiver.
| Letter | Apparatus |
|---|---|
| A | Distillation flask (with the thermometer) |
| B | Water condenser |
| C | Conical flask (receiver) |
Distillation separates liquids whose boiling points differ by at least about 25 °C. It can also separate a liquid from a solution with a dissolved solid.
| Mixture | Boiling points | Difference | Separable? |
|---|---|---|---|
| (a) water — acetone | 100 °C, 56 °C | 44 °C | Yes |
| (b) water — salt | Salt does not boil | Water distils, salt stays | Yes |
| (c) acetone — alcohol | 56 °C, 78 °C | 22 °C | No (less than 25 °C) |
| (d) sand — salt | Both are solids | — | No |
| (e) alcohol — chloroform | 78 °C, 61 °C | 17 °C | No |
| (f) alcohol — benzene | 78 °C, 80 °C | 2 °C | No |
Method: take clear glass tumblers with the samples given below. Darken the room and shine a laser pointer or a torch through each from the side. Look from the side, at right angles to the beam. Never look into the laser beam.
| Sample | Type of mixture | Beam visible? |
|---|---|---|
| Salt or sugar in water | Solution (control) | No |
| Few drops of milk in water | Colloid | Yes |
| Starch or soap solution in water | Colloid | Yes |
| Chalk powder in water | Suspension | Yes |
| Incense (agarbatti) smoke in a jar | Colloid (smoke in air) | Yes |
The particles of colloids and suspensions scatter the light, so the path of the beam is seen. The particles of a solution are too small, so the beam is not seen.
Method: for each compound, make a hot saturated solution in water, filter it, and let it cool slowly and undisturbed in a covered beaker. Filter the crystals and dry them. Observe with a magnifying glass.
Sample observations (your own may differ):
| Compound | Colour | Shape of crystals |
|---|---|---|
| Common salt | Colourless / white | Small cubes |
| Epsom salt | Colourless / white | Long, thin needles |
| Sugar | Colourless / white | Shiny, glassy blocks |
| Borax | Colourless / white | Small, short prisms |
| Nickel sulfate | Green | Small, regular crystals |
| Copper sulfate | Blue | Well-shaped, shiny blocks |
Different compounds make crystals of different shapes and colours.
Method:
1. Crush a few red leaves (for example red amaranth or coleus) in a little alcohol to get a coloured extract.
2. Put a spot of the extract on the pencil line of a strip of chromatography (filter) paper, and let it dry. Repeat 3 to 4 times on the same spot.
3. Dip the lower end of the strip in alcohol. The level of alcohol must be below the spot.
4. Remove the strip when the solvent has risen near the top and mark the solvent front.
Observation: the spot separates into several coloured bands, including a green band, along with red, orange or yellow ones.
Inference: yes, red leaves also contain green pigment (chlorophyll). It is hidden by the red pigments.
Method: put a spot of the food colour (or the colour dissolved from fennel seeds in a little water) on the pencil line of a filter paper strip, dip the lower end in water (or 2% salt solution) and let the liquid rise. Count the coloured spots.
Sample observation (your own may differ):
| Sample | Spots seen | Number of components |
|---|---|---|
| Green food colour | Blue and yellow | 2 |
| Orange food colour | Red and yellow | 2 |
| Yellow food colour | One yellow spot | 1 |
| Coloured fennel seeds | Pink and blue | 2 |
The number of spots is the number of coloured components in the sample.
Game: “Separation Snap” (for 2 to 4 players)
Cards: make two sets of cards. Set 1 has mixtures (sand + water, salt + water, iron + sulfur, camphor + sand, oil + water, black ink, muddy water, acetone + water). Set 2 has methods (filtration, evaporation, magnet, sublimation, separating funnel, chromatography, centrifugation, distillation).
Rules: a player draws a mixture card and must pick the right method card in 30 seconds and give one reason.
Scoring: 2 points for the right method and 1 more for the right reason. A hands-on challenge card asks the player to actually separate a real mixture, for 3 points.
The player with the most points wins.
Set-up using a pot:
1. Pour dirty water into a large pot. Place a small clean cup in the middle, so that it floats or stands on a stone (the cup should not touch the dirty water).
2. Cover the pot with a lid turned upside down, or a plate, with its centre lower than the edge.
3. Heat the pot on a fire. Water vaporises. Keep ice or a wet cloth on the lid so that it is cool.
4. The vapour touches the cool lid, condenses, and drips into the cup.
Result: clean water collects in the cup. The dirt stays in the pot.
States of matter simulation: when the substance is heated, its particles move faster. A solid becomes a liquid and then a gas. When it is cooled, the particles slow down and come close together.
Concentration simulation: adding more solute to the same amount of solvent makes the colour deeper and the concentration higher. Adding more water makes the solution lighter, so it is diluted.
After a certain amount, no more solute dissolves. The solution is then saturated.
Blood does many jobs together: it carries oxygen (red cells), fights infections (white cells), clots at a wound (platelets) and carries nutrients, waste and hormones (plasma).
Scientists have made substances that can carry oxygen for a short time, and are trying to grow red cells in the laboratory.
So far, no artificial blood can do all the jobs of real blood safely for every patient. It is also difficult to match the types of the patients, and to keep it safe, store it and make it at a low cost.
So, donated blood is still needed. Blood donation saves lives.
Every mixture can be classified by particle size — solution, colloid, or suspension — and once you know which one you're dealing with, along with how its components differ in solubility, boiling point, density, or size, there's always a matching separation technique that can pull it apart cleanly.
Seven extra questions in the style of the textbook, for independent practice. Attempt each one on paper first, then tap to check.
| Mixture | Type | Supporting observation |
|---|---|---|
| (a) Sugar in water | True solution | Clear and transparent. A laser beam is not visible and nothing settles |
| (b) Starch in water | Colloid | Looks uniform and does not settle. A laser beam is visible |
| (c) Chalk powder in water | Suspension | Particles settle on standing and are left on the filter paper |
Given: 200 g of water, solubility at 60 °C = 287 g/100 g, solubility at 40 °C = 241 g/100 g
To find: mass of crystals formed
Per 100 g of water:
For 200 g of water:
Check: at 40 °C, 200 g of water can hold 482 g, and 574 − 482 = 92 g.
Given: concentration = 0.9 % m/v, volume of solution = 500 mL
To find: mass of sodium chloride
0.9 % m/v means 0.9 g of sodium chloride in every 100 mL of the solution.
Preparation: dissolve 4.5 g of sodium chloride in some water in a measuring flask, and then add water up to the 500 mL mark.
Step 1: Magnet. Iron is attracted by a magnet. It is taken out first, and it is not affected by heat or water.
Step 2: Sublimation. Heat the rest in a china dish with an inverted funnel. Ammonium chloride sublimes and is deposited on the funnel. Sand and salt remain.
Step 3: Dissolving and filtration. Add water to the left-over mixture and stir. The salt dissolves. The sand is left on the filter paper.
Step 4: Evaporation (or crystallization). Heat the filtrate to evaporate the water, and common salt is obtained.
Why the order matters: ammonium chloride dissolves in water, so sublimation must be done before adding water. If water is added first, ammonium chloride and salt would both dissolve together and be difficult to separate.
Test 1: Leave them undisturbed for a few minutes. The chalk powder settles at the bottom, so that beaker is the suspension (iii).
Test 2: Shine a laser or torch beam through the other two. The beam is visible in milk (colloid) but not in the sugar solution.
Test 3 (to confirm): filter each. Chalk leaves a residue. Sugar solution and milk pass through the filter paper without leaving a residue.
Reasoning: the particles of a suspension are large, so they settle and are filtered out. The particles of a colloid are medium-sized, so they scatter light. The particles of a solution are very small, so they do not scatter light.
| Beaker | Settles? | Beam visible? | Residue on filter? |
|---|---|---|---|
| Sugar solution | No | No | No |
| Milk in water | No | Yes | No |
| Chalk in water | Yes | Yes | Yes |
Difference in boiling points:
Simple distillation works well when the boiling points differ by at least about 25 °C. Here the difference is only 22 °C, which is less.
So both liquids would vaporise together to some extent, and the separation would not be good.
Better method: fractional distillation. It is used when the boiling points of the liquids are close (less than 25 °C apart), as in the separation of crude petroleum.
Given: mass of sugar = 15 g, mass of water = 135 g
Mass of solution = 15 + 135 = 150 g
Let the extra sugar be x g. The mass of water stays the same, so:
Check: sugar = 33.75 g, solution = 168.75 g, and 33.75 ÷ 168.75 × 100 = 20%.
Next up is Chapter 6 — How Forces Affect Motion. Or explore the full chapter list, browse the Class 9 Science hub, or revise with the Class 9 Science Notes, or test yourself with the free Class 9 Science Sample Paper and Marking Scheme.
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