Sorting Materials into Groups – Class 6 Science (NCERT Chapter 4)
In everyday life we handle many materials—plastic bottles, steel utensils, cotton clothes, wooden furniture, glass tumblers, sugar and salt, oil and water. To study them scientifically (and to use them wisely), we classify or sort materials into groups. This chapter builds the habit of observing properties and making sensible groups based on those properties. Below you’ll find simple, exam-ready Notes and a complete set of Questions & Answers (7 MCQs, 7 Very Short, 7 Short, 7 Long) aligned with the Class 6 syllabus.
📒 Easy Notes: Sorting Materials into Groups
Why do we sort materials?
- To make study and usage easier—grouping reduces complexity.
- To select the right material for the right job (e.g., glass for windows, not for hammers).
- To compare and learn patterns: materials with similar properties behave similarly.
- To improve safety and convenience (non-toxic for food containers, insulating handles for utensils, etc.).
Common properties used for grouping
- Appearance/Lustre: Metals (iron, copper, aluminium) usually shine (lustrous) when polished; non-metals like wood, chalk are non-lustrous.
- Hardness: Hard (iron, steel, glass) vs soft (cotton, rubber, clay). Hard resists being scratched/pressed.
- Solubility in water: Soluble (salt, sugar) vs insoluble (sand, oil, plastics). Remember: oil is insoluble and forms a separate layer.
- Transparency: Transparent (clear glass, clean water), translucent (oiled paper, frosted glass), opaque (wood, metals).
- Float/Sink (Density relative to water): Some materials float (dry wood, plastic balls) while others sink (stone, iron nail).
- Conduction of heat: Conductors (metals) vs insulators (wood, plastic, cork). Used for utensil bodies vs handles.
- Conduction of electricity: Metals conduct; rubber, plastic, wood are insulators. Graphite (pencil lead) is a notable non-metal conductor.
- Magnetism: Iron, nickel, cobalt are magnetic; most other common materials are non-magnetic.
- Flexibility: Some are rigid (glass rod), some flexible (rubber tube), some elastic (stretched rubber band returns to shape).
- Miscibility (liquid + liquid): Water + alcohol mix; water + oil don’t mix (immiscible) and form layers.
Examples of sensible groupings
- Kitchen: Metals (pots), ceramics/glass (cups), plastics (bottles), fibres (cotton towels), wood (cutting boards).
- School bag: Paper (notebooks), plastics (covers), metals (staples), fabric (bag body), rubber (eraser).
- Toolbox: Metals (hammers, screws), plastics/wood (handles), rubber (grips), glass rarely used due to brittleness.
Choosing material for use
We match property to purpose. A cooking pan must conduct heat (metal) but the handle must not conduct (wood/plastic). A window must allow light (transparent glass), while a cupboard door can be opaque (wood/metal). A raincoat should be waterproof (PVC or coated fabric).
Transparent, Translucent, Opaque
- Transparent: See clearly through (clean water, glass). Light passes almost completely.
- Translucent: See blur shapes (butter paper, thin fabric). Light passes partially.
- Opaque: Cannot see through (wood, steel). Light does not pass through.
Solubility and solutions
A solution forms when a solute (like sugar) dissolves uniformly in a solvent (like water). Temperature generally increases solubility of solids in water. Insoluble solids (sand) settle; insoluble liquids (oil) float and form a separate layer.
Float and sink
Whether an object floats depends on density compared to water (~1 g/cm³). A heavy-looking big log can float if its average density is less than water, whereas a tiny iron nail sinks because iron’s density is higher.
Conductors and insulators
- Heat conductors: Most metals—used where heat transfer is needed (pots, pans).
- Heat insulators: Wood, plastics, cork—used for handles, grips, insulation.
- Electrical conductors: Metals, graphite—used in wires/electrodes.
- Electrical insulators: Rubber, plastics—used as wire coating for safety.
Magnetic vs non-magnetic
Iron, nickel, cobalt are attracted by magnets. This helps in sorting (e.g., separating iron nails from a mixture using a magnet).
Rigid, flexible, elastic
- Rigid: Keeps shape easily (glass rod, wooden scale).
- Flexible: Can bend without breaking (plastic sheet).
- Elastic: Stretches and returns (rubber band).
Creating a simple classification table (idea for practice)
Take 10 common items and make columns: Appearance, Hard/Soft, Soluble, Transparent Class, Float/Sink, Heat Conductor, Electric Conductor, Magnetic, Flexible. Fill quickly—patterns will pop out and help you answer any “grouping” question in exams.
- “All metals are magnetic” – ❌ Only some (iron, cobalt, nickel) show strong magnetism.
- “All shiny things are metals” – ❌ Many plastics can be shiny; not all shiny = metal.
- “If it disappears, it dissolved” – ❌ Fine powders may settle later; that’s not a true solution.
📝 Questions & Answers (7 MCQ • 7 Very Short • 7 Short • 7 Long)
🔹 A. Multiple Choice Questions (Choose one)
🔹 B. Very Short Answer Questions
1) Define lustre.
Lustre is the shine shown by some materials (especially metals) when polished or freshly cut.
2) Name two soluble substances in water.
Salt and sugar.
3) Give one example of an insulator of heat used in the kitchen.
Plastic or wooden handle of a pan.
4) What are transparent materials?
Materials through which we can see clearly, like clean water or clear glass.
5) Which three metals are strongly magnetic?
Iron, nickel and cobalt.
6) What is meant by immiscible liquids?
Liquids that do not mix uniformly, e.g., oil and water.
7) Why are electrical wires coated with plastic?
Plastic is an insulator; it prevents electric shocks and short circuits.
🔹 C. Short Answer Questions
1) Why do we prefer glass for windows but not for making hammers?
Glass is transparent, allowing light to pass, making it ideal for windows. It is brittle, so it’s unsuitable for tools like hammers that need toughness and impact resistance.
2) Distinguish between transparent and translucent materials with one example each.
Transparent: See clearly through (clear glass). Translucent: Light passes partially; objects appear blurred (butter paper, frosted glass).
3) Mention two differences between conductors and insulators of electricity.
Conductors (like copper) allow electric current to pass and are used in wires; insulators (like rubber) do not allow current and are used as protective coating.
4) Explain, with one reason, why oil forms a layer on water.
Oil is immiscible and less dense than water, so it does not mix and floats as a separate layer.
5) A shiny object is found in a drawer. Is it definitely a metal? Explain.
Not necessarily. Some plastics and glass objects can be shiny. To confirm, test for other metal properties like electrical/heat conduction or magnetism (for iron, nickel, cobalt).
6) Why is aluminium a popular material for cooking utensils?
It conducts heat well, is light in weight, resists corrosion and is relatively affordable—making it suitable for kitchen use.
7) Give one example each of: (a) flexible solid (b) rigid solid (c) elastic solid.
(a) Plastic sheet (flexible) (b) Glass rod (rigid) (c) Rubber band (elastic).
🔹 D. Long Answer Questions
1) What criteria would you use to group a collection of objects from your classroom? Explain with examples.
Begin by observing appearance (lustrous vs non-lustrous), hardness (sturdy metal scissors vs soft eraser), transparency (clear scale vs wooden ruler), and use (writing, measuring, cutting).
Next, consider conduction of electricity (metal paper clips vs wooden pencil), magnetism (iron pins attracted by a magnet), and flexibility (plastic folder vs rigid stapler).
Grouping by these properties helps in storing and using items safely and quickly. For example, keep all metal items together, insulators together, and transparent measuring tools together for easy access.
2) Describe an activity to test the solubility of five substances in water and how you would record the results.
Take five teaspoons labeled salt, sugar, sand, sawdust, and alum. Add each to a separate beaker of equal water volume and stir. Observe whether each substance disappears forming a clear solution or settles as particles.
Record in a simple table with columns: “Substance / Soluble? (Y/N) / Observation.” Salt, sugar, alum will show clear solutions; sand and sawdust will settle.
Conclude that only some substances dissolve in water and solubility is a useful property for grouping.
3) A shopkeeper wants to choose materials for making: (i) transparent jars for sweets, (ii) ladles for hot oil, (iii) decorative but safe lamp shades. Suggest materials with reasons.
(i) Transparent jars: Glass or clear, food-grade plastic (transparent, non-reactive, helps display and preserve).
(ii) Ladles for hot oil: Metal heads (steel) for heat conduction and strength with wooden/plastic handles (insulation).
(iii) Lamp shades: Translucent materials (frosted glass, oiled paper, thin fabric) to diffuse light gently; ensure heat-resistant and safe mounting.
4) Explain with examples how magnetism helps in sorting. What limitations does this method have?
Magnets attract iron, nickel, cobalt, so they can separate iron nails from sand or extract iron filings from a mixture. In recycling, magnetic belts pull out tin/steel cans.
Limitations: Non-magnetic metals (aluminium, copper) won’t be separated by magnets; mixtures containing similar non-magnetic materials still need other methods (density, size sieving, manual sorting).
5) “Floating does not depend only on heaviness.” Justify the statement with suitable examples.
Floating depends on density, not just weight. A large, heavy-looking wooden log floats because its average density is less than water. A small iron nail sinks because iron is denser than water.
Similarly, a ship made of steel floats due to hollow structure increasing overall volume and decreasing average density below that of water.
6) Give a comparative note on transparent, translucent, and opaque materials including two uses for each type.
Transparent (clear glass, clean water) allows clear viewing; uses—windows, spectacles. Translucent (frosted glass, butter paper) allows partial light; uses—lamp shades, privacy panels.
Opaque (wood, metal) blocks light; uses—doors, cupboards. Choosing among them depends on the need for visibility, privacy, and safety.
7) You are given a mixed box of: iron nails, plastic beads, sand, sugar, wooden chips. Plan a two-step sorting strategy and explain why it works.
Step 1: Use a magnet to pull out iron nails (magnetic sorting). Step 2: Add the remaining mixture to water and stir—sugar dissolves (solution), plastic beads and wooden chips float (lower density), sand sinks (higher density).
Filter to remove floating pieces, decant or filter to separate sand, and evaporate the sugar solution to recover sugar.
This strategy uses magnetism and density/solubility differences efficiently.
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