Science — Materials of Daily Use — CTET Mathematics & Science
Ask a Class VII student why ice melts and a candle's wick burns and both "need heat," and you'll often get the same answer for both — "a chemical change." NCERT spends real effort undoing exactly this conflation, because the presence of heat says nothing about whether a change is physical or chemical: melting is reversible and forms no new substance, burning is not reversible and does form new substances. This chapter is where CTET tests that kind of precise, non-interchangeable vocabulary hardest — fibre versus fabric, sieving versus filtration, evaporation versus distillation — dressed up as everyday materials rather than abstract definitions.
1. What CTET actually asks
Science — Materials of Daily Use carries weightPct 5 of the 60-question Mathematics & Science elective section — roughly 3 of those 60 questions, sitting inside the section's ~30-question Science sub-block, each worth 1 mark with no negative marking.
The chapter spans five NCERT strands, and as with every chapter in this subject, expect roughly 70% pure content and 30% pedagogy-of-teaching-this-topic:
- Fibre to fabric — natural fibres (cotton, jute, wool, silk) and synthetic fibres (rayon, nylon, polyester, acrylic), and the spinning-weaving-knitting sequence that turns fibre into cloth.
- Sorting materials into groups — classifying everyday objects by appearance, hardness, solubility, ability to float, and transparency.
- Physical and chemical changes — the reversible/irreversible distinction, and why heat alone doesn't decide the category.
- Separation of substances — the named methods (handpicking, threshing, winnowing, sieving, sedimentation-decantation, filtration, evaporation, distillation) and choosing the right one for a given mixture.
- Synthetic materials and plastics — properties, everyday uses, and environmental concerns.
2. Fibre to fabric
Natural fibres come from two sources. Plant fibres: cotton is harvested from the cotton boll and separated from its seeds by ginning; jute comes from the stem of the jute plant, separated by retting — soaking the stems in water until the surrounding tissue rots away, freeing the fibre. Animal fibres: wool comes from the hair or fleece of sheep, goats, yaks, and camels — sheared from the animal (shearing), then cleaned of grease and dirt (scouring) before spinning; silk comes from the cocoon spun by the silkworm (Bombyx mori is the commonly reared species) — rearing silkworms for silk is called sericulture, and the fibre (made of the protein fibroin) is unwound from the cocoon in a process called reeling.
Synthetic fibres are manufactured from chemical raw materials rather than grown. Rayon is a semi-synthetic fibre — made by chemically treating natural cellulose (wood pulp), which is why it is sometimes mistaken for fully natural. Nylon, developed in 1931, was the first fully synthetic fibre, made entirely from petrochemicals with no natural raw material at all — strong, elastic, and lightweight, used in parachutes, ropes, and stockings. Polyester resists wrinkling and is used in dress material, safety belts, and (as PET) plastic bottles. Acrylic is a wool substitute — cheaper and lighter than wool, though generally less warm, and used in sweaters and blankets.
Turning fibre into fabric involves three distinct processes, and the terms are not interchangeable: spinning twists fibres together into a continuous strand of yarn; weaving interlaces two sets of yarn at right angles on a loom to form fabric; knitting makes fabric from a single yarn by looping it with needles so the loops interlock — knitting can be done by hand or machine, and unlike weaving, it needs only one continuous yarn rather than two interlaced sets.
3. Sorting materials into groups
NCERT introduces material classification through direct comparison of everyday objects across several independent properties:
- Appearance — colour, shape, texture, and lustre (shiny versus dull).
- Hardness — hard materials resist scratching or denting; soft materials do not.
- Solubility — whether a substance dissolves in water (soluble, like salt or sugar) or does not (insoluble, like sand or chalk powder).
- Ability to float or sink — depends on the material's density relative to water.
- Transparency — materials are transparent (see clearly through, like glass or clear water), translucent (see partially/blurred through, like frosted glass or butter paper), or opaque (cannot see through at all, like wood or metal). The middle category, translucent, is the one students most often forget exists at all.
A single property is rarely enough to classify materials meaningfully — the same object can be hard-and-soluble, soft-and-insoluble, and so on — so NCERT's activities deliberately have students sort the same set of objects using more than one property in turn, which is the point rather than a limitation.
4. Physical and chemical changes
A physical change alters a substance's form, size, or state without forming any new substance — the material's chemical composition is unchanged, and many (though not all) physical changes are reversible. Examples: melting of wax or ice, dissolving sugar in water, stretching a rubber band, cutting paper or a tree into pieces.
A chemical change produces one or more genuinely new substances with properties different from the starting material(s), and is generally not reversible by ordinary physical means. Examples: burning of paper or a magnesium ribbon, rusting of iron, the souring of milk, digestion of food. Chemical changes are often signalled by a colour change, gas evolution, a change in temperature, or the formation of a precipitate — useful clues, though none is proof on its own.
Two precise distinctions matter more than the broad definition:
- Heat being involved does NOT make a change chemical. Melting wax needs heat and is purely physical (it re-solidifies on cooling, unchanged); burning the same candle's wick also needs heat, but is chemical (it produces soot, gases, and water vapour — new substances that cannot simply be reversed by cooling). Judge a change by whether a new substance forms, never by whether heat was present.
- Irreversibility does NOT make a change chemical either. Cutting a sheet of paper into pieces is irreversible in the sense that you can't restore the original sheet, yet it remains a physical change — the paper is still paper, chemically unchanged. Nearly all chemical changes are irreversible under ordinary conditions, but the reverse implication does not hold: not every irreversible change is chemical.
Rusting deserves specific attention as a frequently tested chemical change: iron rusts only in the presence of both oxygen and moisture together — dry air alone, or water with no dissolved oxygen, will not rust iron on its own. Rusting is prevented by excluding one or both: painting, oiling, galvanising (coating with zinc), and alloying (as in stainless steel) are the standard methods. Crystallisation — obtaining pure crystals of a substance (like copper sulphate) from a solution — is worth noting as a physical change used deliberately to purify a substance, despite looking dramatic.
5. Separation of substances
Choosing a separation method depends on the physical states of the components, their particle sizes, and their solubility — NCERT names eight distinct methods, and confusing adjacent ones is the most common source of error in this section:
| Method | What it separates | Example |
|---|---|---|
| Handpicking | Slightly larger, visible impurities from a bulk solid | Removing stones from rice or wheat |
| Threshing | Grain from the harvested stalks it grew on, by beating or machine | Separating wheat grains from cut stalks |
| Winnowing | Heavier grain from lighter husk, using wind or blown air | Separating grain from husk after threshing |
| Sieving | Solid particles of different sizes from each other, using a mesh | Separating flour from bran; separating stones from sand |
| Sedimentation & decantation | An insoluble solid that settles from a liquid (sedimentation), then pouring off the clear liquid (decantation) | Settling mud out of muddy water, then pouring off the clear water |
| Filtration | An insoluble solid from a liquid, using filter paper | Separating tea leaves from brewed tea |
| Evaporation | A solid dissolved in a liquid, by driving off the liquid as vapour | Recovering common salt from salt water |
| Distillation | Two miscible liquids, or a dissolved solid AND the pure liquid, by evaporating then condensing in a closed system | Recovering pure water from salt water, retaining both salt and water |
Two distinctions are worth fixing precisely because CTET tests them against each other directly: threshing versus winnowing are sequential, not interchangeable — threshing loosens grain from stalks first, winnowing then separates the loosened grain from husk using wind. Evaporation versus distillation differ in what you keep: evaporation is the right choice when you only want the dissolved solid back (the liquid escapes as vapour into the air and is lost); distillation is the right choice when you want to recover the liquid too, since it condenses the vapour back into a collected, pure liquid rather than letting it escape.
6. Synthetic materials and plastics
Plastics are polymers — long chains of repeating chemical units — and NCERT divides them into two categories based on how they behave under heat: thermoplastics (like polythene and PVC) soften on heating and can be moulded and remoulded repeatedly; thermosetting plastics (like bakelite and melamine) are moulded once and do not soften on reheating afterward, which is exactly why bakelite is used for electrical switches and pan handles — it stays rigid and heat-resistant even near a hot stove or a live circuit.
Plastics share a common set of properties that explain their everyday popularity: they are durable, lightweight, resistant to corrosion and water, chemically non-reactive, and generally poor conductors of both heat and electricity — the same property set that makes them useful also makes them an environmental problem, since a non-biodegradable material that resists decay in use resists decay after disposal just as stubbornly.
The environmental concerns NCERT flags specifically: plastic waste does not decompose naturally and persists in soil and water for a very long time; discarded plastic bags clog drains and are frequently ingested by grazing animals, often fatally; and burning plastic releases toxic gases rather than safely disposing of it. The recommended response is the reduce, reuse, recycle principle — minimising use of thin, single-use plastic in the first place, reusing sturdier plastic items, and recycling what can be recovered — rather than treating any single action alone as sufficient.
7. Solved PYQ-style examples
Q1. Which of the following is a natural animal fibre? Solution. Wool is sheared from the fleece of sheep and other animals — a genuine natural animal fibre, unlike rayon (semi-synthetic, from wood pulp) or nylon and polyester (fully synthetic, from petrochemicals). Answer: Wool.
Q2. The process of separating jute fibres from the stem of the jute plant by soaking it in water until the surrounding tissue rots away is called: Solution. This retting process, distinct from ginning (used for cotton) or reeling (used for silk), is specifically how jute fibre is freed from its stem. Answer: Retting.
Q3. Which of the following is an example of a chemical change? Solution. Rusting of an iron nail produces a new substance (iron oxide) with different properties from iron, and is not reversible by ordinary physical means — unlike melting, dissolving, or cutting, all of which are physical changes. Answer: Rusting of an iron nail.
Q4. A mixture of sand, salt, and water needs to be separated so that pure water, pure salt, AND sand are all recovered separately. Which sequence of methods achieves this? Solution. Filtration first removes the insoluble sand; the remaining salt-water filtrate is then distilled — not merely evaporated — so that both the pure water (collected as distillate) and the pure salt (left behind) are recovered, rather than losing the water to the air as evaporation alone would. Answer: Filtration, then distillation.
Q5. Bakelite is used to make electrical switches mainly because, being a thermosetting plastic, it: Solution. Thermosetting plastics like bakelite do not soften once moulded, even under heat, and are poor conductors of electricity — exactly the two properties an electrical switch housing needs near a live circuit. Answer: Does not soften on reheating, and is a poor conductor of electricity.
Q6. A teacher gives a mixed box of buttons, marbles, spoons, and pebbles to a Class VI class and asks students to sort the objects into groups using their own criteria, before naming any category. This activity primarily supports which pedagogical goal from NCF 2005's approach to early science teaching? Solution. Free, criteria-generating sorting builds the concept of classification inductively, from the learner's own direct manipulation of real objects, rather than handing down a fixed classification scheme to be memorised. Answer: Building classification as a concept, inductively, through hands-on sorting.
8. Common traps
- Confusing sieving with filtration — sieving separates solid particles of different sizes from EACH OTHER (a solid-solid mixture); filtration separates an insoluble solid from a liquid (a solid-liquid mixture). They are not the same operation applied to different materials.
- Assuming any change involving heat is chemical — melting wax needs heat and is physical (reversible, no new substance); burning the same wax's wick needs heat and is chemical (irreversible, new substances form). Judge by whether a new substance forms, not by the presence of heat.
- Assuming every irreversible change is chemical — cutting paper or breaking glass is irreversible but remains physical, since no new substance is formed; irreversibility alone does not prove a change is chemical.
- Treating evaporation and distillation as interchangeable — evaporation recovers only the dissolved solid, losing the liquid as vapour to the air; distillation recovers the liquid too, by condensing the vapour in a closed system. Use evaporation when you only want the solid; use distillation when you want the liquid back as well.
- Treating threshing and winnowing as the same step — threshing loosens grain from harvested stalks first; winnowing then separates the loosened grain from husk using wind. They are sequential, not synonyms.
- Calling rayon a fully natural fibre — rayon is semi-synthetic: its raw material (cellulose from wood pulp) is natural, but it is chemically processed into fibre form, unlike a fully natural fibre such as cotton or wool.
- Assuming all plastics can be remoulded by reheating — this is only true of thermoplastics; thermosetting plastics like bakelite are moulded once and do not soften again on heating, which is precisely why they're chosen for heat-exposed items like switches.
- Forgetting translucent as a distinct transparency category — materials are transparent, translucent, OR opaque; treating transparency as a strict either/or between "see through" and "can't see through" skips the middle category NCERT explicitly tests.
- Underrating sorting/classification activities as a mere warm-up — NCF 2005 treats hands-on sorting by real, self-chosen criteria as a genuine concept-formation tool for younger learners, not a preliminary exercise before the "real" content — a distinction CTET's pedagogy questions test directly.
9. Training protocol
Because this chapter's weight is light, prioritise the vocabulary pairs that CTET most often tests against each other rather than trying to memorise every fact with equal depth: sieving vs filtration, evaporation vs distillation, threshing vs winnowing, and thermoplastic vs thermosetting are the four highest-yield distinctions, since a wrong choice within each pair is the standard distractor design in this chapter. For physical-versus-chemical-change questions, train yourself to ask "did a new substance form?" as the only real test — not "was heat involved?" and not "can it be undone?," both of which are unreliable shortcuts that this chapter is specifically designed to expose. For the roughly 30% of questions framed as pedagogy, default to the option where learners physically sort, test, or handle materials using their own criteria — that is consistently NCF 2005's preferred answer over any lecture-based or textbook-only alternative. As with every CTET Paper 2 chapter, there is no negative marking, so never leave a question in this section unattempted once even one clearly wrong option has been ruled out.
