This MCQ module is based on: Sieving, Sedimentation, Decantation and Filtration
TOPIC 32 OF 46
Sieving, Sedimentation, Decantation and Filtration
🎓 Class 6
Science
CBSE
Theory
Ch 9 — Methods of Separation of Substances
⏱ ~14 min
🌐 Language: [gtranslate]
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9.6 Sieving — When the Sizes Are Just a Little Different
Sometimes the things in a mixture are both small, and the wind is too gentle to separate them. Think of wheat flour in which some bran (the big rough bits) has been left behind. Handpicking is impossible — the flour is a fine powder! In such cases we use sieving.
In sieving, a sieve (chalni) has many tiny holes of a fixed size. When we pour the mixture on top and shake it, the small particles slip through the holes and the bigger particles are left behind on the sieve.
Sieve / Chalni: a tool with a mesh of fine holes. Whatever is smaller than the hole falls through; whatever is bigger stays on top.
Sieving is used in many places you already know:
Flour mills
Mills use huge shaking sieves to separate fine wheat flour from coarse bran.
Building sites
Workers sieve sand to remove big pebbles before mixing cement.
Baking at home
Bakers sieve flour to remove lumps and make a smooth, soft cake batter.
Activity 9.3 — Build Your Own Sieve Test L3 Apply
You need: a kitchen sieve (chalni), 1 cup wheat flour, 1 tbsp suji (semolina), 1 tbsp rice, a clean bowl.
- Mix the flour, suji, and rice gently in a plate.
- Hold the sieve over the empty bowl and pour the mixture on it.
- Shake the sieve from side to side.
- Observe: what falls into the bowl? What stays in the sieve?
Predict: If we used a sieve with bigger holes, would the suji also fall through? Why?
Observation: Only the fine flour falls into the bowl. The suji and rice stay on top because they are bigger than the holes. A sieve with bigger holes would let suji pass — sieving depends entirely on the size of the holes.
9.7 Sedimentation and Decantation — Letting Heavy Bits Settle
What if the thing we want to separate cannot be picked up by hand, blown away by wind, or pushed through a sieve? This happens a lot with muddy water. The mud is mixed all through the water — too fine to sieve, too tiny to handpick. Here we use two methods together: sedimentation and decantation.
Step 1 — Sedimentation
Pour the muddy water into a tall glass and leave it still. After some time, you will notice that the mud slowly sinks to the bottom. This settled layer at the bottom is called the sediment. The water above becomes much clearer.
Step 2 — Decantation
Once the mud has settled, we very gently tilt the glass and pour out the clear water into another container. This slow pouring is called decantation. The mud stays back — we have separated it from the water!
In homes long ago: Many Indian homes stored drinking water in a tall clay pot overnight. By morning, sediment had gathered at the bottom, and the water on top was clear and cool to drink.
9.8 Filtration — The Cloth and the Filter Paper
Sedimentation works only when the mud is heavy enough to settle. But what about tea leaves in tea, or very fine particles that float in the liquid and never fully settle? For these, we use filtration.
A filter is any material with very tiny holes — much smaller than even sieve holes. Common filters are muslin cloth (malmal), filter paper, and even cotton wool. The liquid passes through, leaving the solid particles stuck on the filter.
Everyday Examples
- Tea strainer (chai-chaalni): pours clear tea into the cup while the wet tea leaves stay back.
- Coffee filter: the decoction (clear coffee) drips through while the ground beans stay in the filter.
- Muslin cloth: used to strain dahi or to make paneer at home.
Filtrate & Residue: The clear liquid that passes through the filter is called the filtrate. The solid left behind on the filter is called the residue.
Activity 9.4 — Cleaning Muddy Water Step-by-Step L4 Analyse
You need: a glass of muddy water, an empty glass, a small square of muslin cloth, a rubber band, a funnel (or a paper cone).
- Let the muddy water sit still for 15 minutes. Observe the mud layer that settles at the bottom.
- Slowly decant (tilt and pour) the water on top into a second glass. Do not disturb the sediment.
- The water may still look a little cloudy. Now tie the muslin cloth over the mouth of a third glass with a rubber band.
- Pour the decanted water through the muslin into the third glass.
- Compare the three stages of water.
Predict: Will the water after filtration be safe to drink straight away? Why or why not?
Observation: Each step made the water clearer — sedimentation removed the heavy mud, decantation took us away from the sediment, and filtration caught the fine cloudy bits. But even now the water is not safe to drink. Tiny germs are still present! We need boiling or purification before drinking.
9.9 Magnetic Separation — A Cool Trick with Iron
Sometimes one thing in the mixture has a special property — like being pulled by a magnet. Iron, nickel, and cobalt are all magnetic. If a mixture has iron pins mixed with sand or iron filings mixed with sulphur powder, we can use a magnet to lift out the iron!
This method is called magnetic separation. It is used at huge junkyards to pull steel scrap from heaps of non-magnetic rubbish, and at cement factories to remove iron bits from the raw material.
9.10 Which Method When? — A Quick Guide
| Mixture | Best method | Property used |
|---|---|---|
| Flour + bran | Sieving | Size difference |
| Muddy river water | Sedimentation + Decantation | Mud is heavier than water |
| Tea leaves in tea | Filtration | Solid bits bigger than filter holes |
| Iron pins in sand | Magnetic separation | Iron is attracted by magnet |
| Sand + small pebbles | Sieving | Pebbles bigger than sieve holes |
Competency-Based Questions
Nisha fetched a bucket of water from the village well. The water looks brown — mud has mixed in from last night's rain. She also notices a few small iron nails that have fallen into the bucket, and a layer of fine powdery dust floating on top.
Q1. Which method should Nisha use to take out the iron nails first? L2
B — Magnetic separation. Iron is magnetic, so a magnet can easily lift the nails out of the water without disturbing anything else.
Q2. After the nails are out, what should Nisha do next to separate the mud? Explain the two steps. L3
(i) Sedimentation — keep the bucket still for some time so that the mud sinks to the bottom. (ii) Decantation — gently tilt and pour the clear water on top into another vessel, leaving the mud behind.
Q3. Even after decantation, the water looks a little cloudy. Which method should she use now? L3
Filtration — she can tie a muslin cloth over a clean pot and pour the cloudy water through it. The fine dust and tiny bits will be caught by the cloth, leaving cleaner water.
Q4. Fill in the blank: The solid left behind on a filter paper is called the ______. L1
Residue. The clear liquid that passes through is called the filtrate.
Q5. Can we use a sieve to separate salt from water? Give a reason. L4
No. Salt completely dissolves in water — its tiny particles mix with the water particles. Sieve holes and filter paper holes are far too big to stop dissolved salt. We need a different method like evaporation to get salt back from water.
Assertion – Reason
Assertion (A): A sieve can separate flour from bran.
Reason (R): Flour particles are smaller than the sieve holes, while bran pieces are bigger.
Answer: A. The whole idea of sieving depends on the difference in size. R correctly explains A.
Assertion (A): Filtration can separate tea leaves from tea.
Reason (R): Tea leaves dissolve completely in water.
Answer: C. A is true — a tea strainer is a classic filter. But R is false: tea leaves do not dissolve; they just swell and float. That is exactly why filtration works on them.
Assertion (A): Sedimentation works well for muddy water.
Reason (R): Mud particles are heavier than water and slowly sink to the bottom when the water is left still.
Answer: A. Heavier mud particles do settle under gravity, leaving clearer water on top. R is the correct reason for A.
Frequently Asked Questions — Sieving, Sedimentation, Decantation and Filtration
What does the topic 'Sieving, Sedimentation, Decantation and Filtration' cover in Class 6 Science?
The topic 'Sieving, Sedimentation, Decantation and Filtration' is part of NCERT Class 6 Science Chapter 9 — Methods of Separation in Everyday Life. It covers the key ideas of sieving, sedimentation, decantation, filtration, filter paper, suspension, solid-liquid separation, explained through everyday examples, labelled diagrams and hands-on activities from the NCERT Curiosity textbook. Class 6 students learn simple definitions, see why each idea matters in daily life, and try short experiments and observations. The lesson uses easy language, colourful pictures and small questions so that young learners build a strong base for higher classes and for competency-based questions in CBSE school tests.
Why is 'Sieving, Sedimentation, Decantation and Filtration' important for Class 6 NCERT Science?
'Sieving, Sedimentation, Decantation and Filtration' is important because it builds the first ideas of science that Class 6 students will use again in Class 7, 8 and beyond. NCERT Chapter 9 — Methods of Separation in Everyday Life — introduces sieving and connects it to things children already see at home, at school and in nature. Learning this topic helps students ask better questions, understand simple news about science, and score well in CBSE tests that use competency-based questions. The chapter also supports NEP 2020 by encouraging curiosity, observation and learning by doing rather than only reading and memorising.
What are the key ideas students should remember from Sieving, Sedimentation, Decantation and Filtration?
The key ideas in 'Sieving, Sedimentation, Decantation and Filtration' for Class 6 Science are: sieving, sedimentation, decantation, filtration, filter paper, suspension, solid-liquid separation. Students should be able to say each term in their own words, give one or two easy examples from daily life, and draw a small labelled diagram where needed. A good way to revise is to make flashcards, write a short note in the science notebook, and solve the NCERT in-text and exercise questions of Chapter 9. Linking every idea to something seen at home or school — in the kitchen, garden, playground or sky — makes these ideas easy to remember for unit tests and the annual CBSE examination.
How is Sieving, Sedimentation, Decantation and Filtration taught using activities in NCERT Curiosity Class 6?
NCERT Curiosity Class 6 Science teaches 'Sieving, Sedimentation, Decantation and Filtration' through an inquiry-based approach using Predict–Observe–Explain activities. Students first make a guess, then try a small experiment with safe, easily available materials, and finally explain what happened and why. This matches the NEP 2020 focus on learning by doing. For Chapter 9 — Methods of Separation in Everyday Life — the textbook has hands-on tasks, labelled pictures and thinking questions built for Bloom's Taxonomy Levels 1 to 6. Teachers use these activities, along with competency-based questions (CBQs) and assertion–reason items, to check real understanding instead of only rote learning.
What real-life examples of sieving can Class 6 students see at home?
Class 6 students can see sieving at home in many simple ways linked to 'Sieving, Sedimentation, Decantation and Filtration'. Kitchens, school bags, playgrounds, the garden and the night sky are full of examples that match NCERT Chapter 9 — Methods of Separation in Everyday Life. For example, students can look at food labels, watch changes while cooking, try safe activities with water, magnets or shadows, and observe the Sun, Moon and weather each day. Keeping a small science diary — with the date, what was observed and a quick drawing — turns daily life into a mini science lab. These real-life links make concepts easy to remember and help in answering competency-based questions in CBSE Class 6 Science.
How does 'Sieving, Sedimentation, Decantation and Filtration' connect to other chapters of Class 6 Science?
'Sieving, Sedimentation, Decantation and Filtration' connects to many other chapters in NCERT Class 6 Science Curiosity. The ideas of sieving come back when students study related topics like diversity in the living world, food, magnets, measurement, materials, temperature, water, separation, habitats, natural resources and the solar system. For example, what students learn here helps them build mental pictures for later chapters and for Class 7 and Class 8 Science. Teachers often ask cross-chapter questions in CBSE exams to check if students can use what they learned in Chapter 9 — Methods of Separation in Everyday Life — in new situations. This linked approach matches the NEP 2020 and NCF 2023 focus on holistic, competency-based learning.
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