Separation of Substances – Class 6 Science Chapter 5 (Notes + Q&A)
This page gives you easy, exam-ready notes and a complete question bank for Separation of Substances (NCERT Class 6 Science, Chapter 5). You’ll learn why we separate mixtures, how to choose the right method, and how to explain steps in answers—followed by 28 practice questions: 7 MCQs, 7 Very Short, 7 Short, and 7 Long answers.
📒 Notes: Separation of Substances (Made Simple)
1) What is a mixture?
A mixture contains two or more substances combined together without any chemical change. Example: sand + salt; water + sugar; pulses mixed with stones. Mixtures may be of solids, liquids, or gases.
2) Why do we separate substances?
We separate to: (a) remove harmful/impure components (stones from rice), (b) obtain useful components (salt from seawater), (c) purify substances (filter muddy water), and (d) obtain materials in the form we want (cream from milk, then ghee).
3) Types of mixtures you’ll see in Class 6
- Solid–solid (wheat + husk, pulses + stones)
- Solid–liquid (sand in water: insoluble; salt in water: soluble)
- Liquid–liquid (oil and water: do not mix well/immiscible)
4) Handpicking
Used when the impurities are larger and visible (stones, leaves). Simply pick out by hand. Works when the quantity is small and components differ in size.
5) Threshing & Winnowing
Threshing separates grains from stalks (by beating/using machines). Winnowing uses wind to blow away lighter husk from heavier grains. Farmer pours the mixture from a height; wind carries away husk.
6) Sieving
A sieve with holes of fixed size lets smaller particles pass through and retains bigger ones. Used in kitchens (refining flour), at construction sites (sand from pebbles).
7) Sedimentation, Decantation & Filtration (for insoluble solids in liquids)
Sedimentation: Let the mixture stand; heavy particles settle at the bottom as sediment.
Decantation: Gently pour the clear liquid (supernatant) into another container without disturbing sediment.
Filtration: Use filter paper or cloth. Liquid (filtrate) passes, solid (residue) remains on filter.
8) Evaporation (for soluble solids)
Heat the solution; water evaporates and the solid (like salt) remains. Example: obtaining salt from seawater at salt pans.
9) Condensation (to get water back)
Water vapour cools to become liquid water again. Evaporation + condensation together show how we can recover water (principle behind distillation in higher classes).
10) Using a Magnet
If one component is magnetic (iron filings) and the other is not (sand), a magnet pulls out the iron.
11) Insoluble vs. Soluble; Miscible vs. Immiscible
- Insoluble: does not dissolve in a liquid (sand in water).
- Soluble: dissolves (salt/sugar in water).
- Immiscible liquids: do not mix well (oil + water); can separate by letting layers form and then pouring out one layer.
12) Choosing the right method (quick guide)
- Solid + solid (different size): handpicking, sieving, winnowing.
- Insoluble solid + liquid: sedimentation → decantation → filtration.
- Soluble solid + liquid: evaporation (Class 6 level).
- Magnetic + non-magnetic solids: magnet.
- Two immiscible liquids: allow to settle into layers, pour off upper layer.
📝 Questions & Answers (28 Practice Qs)
I) Multiple Choice Questions (7)
1. Which method best separates husk from wheat grains?
A) Handpicking B) Filtration C) Winnowing D) Evaporation
Answer: C. Husk is lighter and blows away from heavier grains.
2. To separate sand from water, the first step you would try is:
A) Evaporation B) Sedimentation C) Magnetic separation D) Sieving
Answer: B. Let heavy sand settle, then decant/filter.
3. Which method is suitable for getting salt from seawater?
A) Decantation B) Sieving C) Evaporation D) Winnowing
Answer: C. Water evaporates; salt remains.
4. Oil and water can be separated because they are:
A) Soluble B) Magnetic C) Immiscible D) Same density
Answer: C. They form layers; pour off the top.
5. Removing iron filings from sand is best done by:
A) Decantation B) Magnet C) Filtration D) Sieving
Answer: B. Iron is magnetic.
6. The clear liquid above the sediment is called:
A) Residue B) Solute C) Supernatant D) Filtrate
Answer: C. Filtrate is what passes through a filter; supernatant is the clear layer after settling.
7. Which is not a use of filtration?
A) Remove tea leaves from tea B) Separate chalk from water C) Separate salt from water D) Clarify muddy water
Answer: C. Salt is dissolved; use evaporation.
II) Very Short Answer (7)
1. Define mixture.
Ans: A mixture has two or more substances combined without chemical change.
2. What is sedimentation?
Ans: Settling of heavy insoluble particles at the bottom of a liquid.
3. Name the liquid obtained after filtration.
Ans: Filtrate.
4. Which method separates flour from bran?
Ans: Sieving.
5. Name one magnetic material used in separation.
Ans: Iron (iron filings).
6. Which method would you use to obtain pure salt from salt solution at Class 6 level?
Ans: Evaporation.
7. What do we call the solid left on filter paper?
Ans: Residue.
III) Short Answer (7)
1. Why is winnowing effective for separating husk from grain?
Ans: Husk is lighter than grain. When the mixture is dropped from a height, wind carries husk away while heavier grains fall vertically. The difference in weight (density) makes winnowing effective.
2. How would you separate stones from pulses and iron filings from sand?
Ans: Stones from pulses: handpicking (visible, larger impurities). Iron from sand: magnetic separation using a magnet to attract iron filings.
3. Explain decantation with an example.
Ans: After sedimentation of sand in water, the clear supernatant liquid is gently poured into another vessel without disturbing the sediment. This pouring step is decantation.
4. Why doesn’t filtration separate salt from salt solution?
Ans: Salt dissolves to form tiny particles smaller than the pores of the filter paper; they pass through with water. Hence, evaporation is needed.
5. Give two daily-life examples of sieving.
Ans: (i) Sieving flour in kitchens to remove bran/lumps. (ii) At construction sites, sieving sand to remove pebbles.
6. What is the role of evaporation and condensation in water recovery?
Ans: Evaporation turns liquid water into vapour; condensation cools vapour back to liquid. Together, they help recover water from solutions (principle shown in simple setups).
7. A child mixes oil and water and shakes the bottle. How can she separate them?
Ans: Let the mixture stand. Oil (lighter) forms an upper layer and water a lower layer. Carefully pour off the oil or use a separating arrangement.
IV) Long Answer (7)
1. Describe the steps to separate a mixture of sand and water completely.
Ans: First, allow sedimentation: sand settles at the bottom because it is heavier and insoluble. Second, perform decantation by gently pouring the clear supernatant into another container. Finally, if tiny particles remain, use filtration with cloth or filter paper. The liquid passing through is the filtrate; sand left behind is residue. Dry the residue to obtain sand completely. Each step improves purity and is easy to describe in exams.
2. Explain how salt is obtained from seawater and why this method works.
Ans: Seawater is collected in shallow pans. Under sunlight and wind, water evaporates gradually, leaving behind salt crystals. This method works because water changes to vapour at ordinary temperatures when exposed for long; dissolved salt cannot evaporate and remains as a solid. The process is cost-effective in hot, dry, windy climates, and it demonstrates a real-life application of evaporation learned in Class 6.
3. Differentiate between mixtures requiring filtration and those requiring evaporation with two examples each.
Ans: Use filtration when the solid is insoluble (e.g., chalk in water; sand in water). The filter’s pores trap solids as residue. Use evaporation when the solid is soluble (e.g., sugar solution; salt solution). Heating drives off water, leaving solid behind. The key is to check whether the solid dissolves; your method depends on that test.
4. A household mixture contains rice, stones, and husk. Explain a complete plan to obtain clean rice.
Ans: First, use winnowing to remove husk because it is lighter than rice; wind blows husk away. Next, apply handpicking to remove remaining visible stones. If dust remains, wash the rice in water and decant the water quickly to avoid grain loss. Writing the plan in steps shows method selection based on size/weight differences.
5. What is sieving? State its principle and two conditions needed for it to work well.
Ans: Sieving separates particles by size using a sieve with uniform holes. Smaller particles pass; larger ones are retained. Conditions: (i) Components must differ significantly in size; (ii) Mixture should be dry and free-flowing so that smaller particles can pass smoothly. Examples include sieving flour and construction sand.
6. Why is filtration preferred over decantation in some cases? Give an example with reasoning.
Ans: Decantation may leave tiny suspended particles that do not settle fast or get disturbed while pouring. Filtration removes even fine insoluble particles by trapping them in the filter’s tiny pores. For muddy water, filtration through cloth or filter paper gives clearer water than simple decantation, improving purity and appearance.
7. Describe a classroom activity to show evaporation and condensation together.
Ans: Heat a salt solution gently in a beaker; cover the beaker partially with a cool metal plate. You will observe vapour rising (evaporation). Water droplets form on the underside of the cool plate (condensation). After sufficient heating, salt crystals remain in the beaker, proving that dissolved solids stay back when water evaporates. This simple activity connects concepts and makes your long answer easy to score.
){kind=link}
0 Comments