NCERT Solutions for Class 9th Science Chapter 5 Projects and investigations — The Journey Beyond

Book page 93 Updated on2026-09-08

Q1.

Demonstrate the Tyndall effect using different colloids. Create a series of experiments showcasing how light scatters in colloids making the beam visible. Use laser pointers (Safety first: Use it under the supervision of an adult), flashlights, or other light sources for your demonstrations.

Answer

What a good demonstration must contain: at least one true solution as a control, several colloids, and the beam observed from the side at right angles each time — so that the difference is a comparison and not just a single observation.

Sample plan

Take five identical glass tumblers. Fill them with: (1) plain water, (2) a clear sugar or salt solution, (3) water with two drops of milk, (4) water with a few drops of soap solution shaken with a drop of oil, (5) very dilute starch paste in water.
Darken the room. Shine a laser pointer or a narrow torch beam through each tumbler in turn, and look at the beam from the side, at right angles to it.
Record for each: is the path of the beam visible? Is it bright or faint?

Sample	Type of mixture	Expected observation
Water; sugar solution	Solution	Beam path invisible
Diluted milk	Colloid (emulsion)	Beam path clearly visible
Soap and oil in water	Colloid (emulsion)	Beam path visible
Dilute starch paste	Colloid	Beam path visible

What the demonstration proves: the samples all look clear or nearly clear to the eye, yet the beam behaves quite differently in them. That difference can only come from particle size — the colloidal particles are large enough to scatter light, the dissolved particles are not. The Tyndall effect is therefore a practical test for telling a colloid from a true solution when the eye cannot.

Safety first: never look into the laser beam or point it at anyone. Use it only under the supervision of an adult.

Q2.

Make crystals of different compounds (common salt, epsom salt, sugar, borax, nickel sulfate, etc.). Observe them under a magnifying glass or a microscope. Note down their colours and shapes.

Answer

Method. For each compound, dissolve it in warm water until no more will dissolve — a saturated solution. Filter it while warm, pour it into a clean, undisturbed container, cover it, and let it cool slowly. Leave it for a day or two, then lift out the crystals, rinse them with a little cold water and dry them on a watch glass. Examine each under a magnifying glass and sketch what you see.

Compound	Colour	Typical crystal shape
Common salt (sodium chloride)	Colourless / white	Cubes
Sugar	Colourless	Long six-sided blocks (as in mishri)
Epsom salt (magnesium sulfate)	Colourless	Long needles
Borax	White	Short prisms
Copper sulfate / nickel sulfate	Blue / green	Slanted blocky crystals

Why each compound has its own shape: a crystal is a solid whose particles are arranged in a regular geometric pattern. That pattern is fixed by the sizes of the particles and the way they attract one another, and it is different for every compound. Because the pattern repeats identically in all directions, the outward shape of the crystal reflects the inner arrangement — which is why every grain of table salt is a little cube. Cool the solutions slowly: this is exactly the experiment of Activity 5.3, and slow cooling is what gives large, well-formed crystals.

Q3.

Do red leaves also contain green pigments? Investigate it using paper chromatography.

Answer

Expected answer: yes, most red leaves also contain chlorophyll — the red pigment simply masks it. Paper chromatography can reveal the green.

Method

Grind a few red leaves (croton, red amaranth or a red coleus leaf) in a mortar with a little sand and 5 mL of alcohol to get a coloured extract. Do the same with an ordinary green leaf as a control.
Draw a pencil line 2 cm from the bottom of a strip of chromatography paper and put a small spot of the extract on the line. Let it dry and add another spot on top, several times, so that the spot is concentrated but small.
Stand the strip in a jar containing a thin layer of alcohol, with the solvent level below the spot. Cover the jar and leave it undisturbed.
When the solvent has risen nearly to the top, take the strip out, mark the solvent front, and let it dry.

What you should see: the single spot separates into several bands — usually a red or purple band, a green band of chlorophyll and often a yellow-orange band of carotenoid. The green band proves that the red leaf does contain chlorophyll.

Why the pigments separate: each pigment is held by the paper and dissolved by the alcohol to a different degree. A pigment that dissolves readily and clings weakly is carried far up the strip; one that clings strongly is left near the start. Since no two pigments have the same balance, each stops at its own height. And why is a green pigment invisible in a red leaf? Because the red pigment absorbs and reflects light far more strongly, so it hides the green from the eye — but chromatography separates the pigments physically, so hiding is no longer possible.

Q4.

You can try chromatography to find the number of components present in a food colour (green, orange, yellow, etc.) or in coloured mouth fresheners (fennel seeds).

Answer

Method. Dissolve a little of the food colour, or soak the coloured coating off a few sugar-coated fennel seeds, in a few drops of water. Spot the coloured liquid on the pencil line of a chromatography strip, dry it, and stand the strip in water (or in 2 % m/v salt solution) with the solvent level below the spot. Let the solvent rise, then dry the strip.

How to read the result

Count the spots. The number of separate coloured spots is the number of components (dyes) in that colour.
Note the order. The spot nearest the top is the dye most attracted to the solvent and least held by the paper.
Compare colours. Run a green food colour and a yellow one side by side; you will often find that the green separates into a blue and a yellow spot, and that the yellow spot matches the pure yellow dye.

Sample	Typical result	Conclusion
Green food colour	Two spots — blue and yellow	A mixture of two dyes
Orange food colour	Often a red and a yellow spot	A mixture
Coloured fennel-seed coating	One or more spots depending on the brand	Shows which dyes have been used

Why chromatography can count components: the method separates by rate of travel, and each substance has its own rate. So one spot on the finished strip means one substance. This is why chromatography is used in food-testing laboratories to check which colours have been added to a sweet or a drink, and in hospitals to identify substances in blood and urine.

Q5.

Design an educational game where players identify and apply separation techniques to different mixtures through interactive challenges and hands-on activities.

Answer

What a good game must contain: a mixture, a reason to think about which property differs between its components, and immediate feedback on whether the chosen technique would actually work.

Sample answer — “Separation Snap”

Materials. Two sets of cards. Mixture cards: sand + salt, oil + water, camphor + sand, muddy water, blood, black ink, seawater, acetone + water, brass, sugar + water. Technique cards: filtration, sublimation, separating funnel, centrifugation, coagulation, chromatography, distillation, evaporation, crystallization, “cannot be separated by physical methods”.
How to play. Turn over a mixture card. The first player to lay down a correct technique card wins the pair — but only if they can also name the property being used (size, solubility, density, boiling point, ability to sublime, rate of travel on paper). Wrong reason, no point.
Chain rounds. Some mixture cards, such as sand + salt + naphthalene, need three technique cards laid in the right order. Double points for the correct sequence.
Trap cards. Brass carries the answer “cannot be separated by physical methods” — the metals are mixed at the level of atoms. Anyone who plays a technique card for it loses a turn.
Hands-on round. Every fifth turn, the group actually performs the separation at the bench with the apparatus provided.

Why the game teaches the chapter: it forces the one habit that matters — before choosing a technique, ask in which property the components differ. Naming the property is worth more than naming the method, because that is the reasoning a student must reproduce in a new, unseen situation.

Q6.

If you are camping outdoors and running short on clean water, you can obtain clean water by distillation. Can you think of a set-up with the items available to you?

Answer

Yes. A camp still needs only three things: a way to heat the dirty water, a cool surface for the vapour to condense on, and a container to catch the drops.

Sample answer — the pot-and-lid still

Half fill a large cooking pot with the muddy or salty water. Stand a small empty cup inside the pot, on a stone, so that its rim is above the water level.
Cover the pot with its lid turned upside down, so the lid slopes towards the centre and its lowest point is directly above the cup.
Put a few pieces of cold stone, or a cloth soaked in cold water, on top of the inverted lid to keep it cool.
Heat the pot gently on the camp fire. Water vaporises, the vapour rises and touches the cold lid, condenses into drops, runs down to the lowest point of the lid and drips into the cup.
After some time, take out the cup. It contains clean distilled water; the mud, salt and germs stay behind in the pot.

Solar version, if there is no fire. Dig a pit, put a container in the middle, pour the dirty water around it, and stretch a clear plastic sheet over the pit weighted with a small stone at the centre. The sun evaporates the water, the vapour condenses on the underside of the sheet and drips off the low point into the container.

Why the water that drips is safe: only the water itself vaporises. Dissolved salts, mud particles and most germs are non-volatile — they cannot enter the vapour — so they stay in the pot. What condenses on the cool surface is therefore water alone. That is exactly the principle of the laboratory distillation set-up of Fig. 5.12: the inverted lid is doing the job of the condenser, and the cup is the receiver.

Safety first: handle the hot lid with a cloth, and let an adult manage the fire.

Was this helpful? Report an error