Methods of Separation in Everyday Life – Case-based Questions with Answers
Class 6
Science
Chapter 9
Methods of Separation in Everyday Life — Case-Based Questions (20)
CBSE Board Examinations
Answer in steps where needed. Mention the method used and the property exploited.
How to use these case-based questions
- Read each short case carefully, then answer the questions that follow in 3–5 clear sentences.
- Always name the separation method and explain the physical property used (e.g., solubility, particle size, magnetism, boiling point).
- These are ideal for section A/B style case-based questions in school tests and CBSE sample papers.
Case-Based Questions
1Cleaning Muddy Water
Case: Riya fills a jar with muddy pond water to water her plants, but the water has visible soil particles. She lets the jar stand overnight.
Q: Which separation methods should Riya use to make the water clearer before using it for plants? Explain steps and why each method is chosen.
A: First use sedimentation by letting the water stand so heavier soil particles settle. Then perform decantation to pour off the clearer water without disturbing sediment. Finally, pass the decanted water through a filter (filtration) like cloth or sand to remove remaining fine particles. These steps use gravity (settling), careful pouring, and size-based filtration to progressively remove suspended solids.
2Tea Preparation
Case: Arjun makes tea and wants to pour it into cups without tea leaves. He has a strainer and a muslin cloth available.
Q: Which method should he use and why? What will be residue and filtrate?
A: Use filtration by pouring tea through the strainer or muslin cloth. The residue will be the tea leaves retained on the filter, while the filtrate is the clear tea collected below. Filtration separates insoluble solid particles (leaves) from the liquid based on particle size.
3Salt from Seawater
Case: A coastal village collects seawater to obtain salt by leaving it in pans under the sun.
Q: Name and describe the method used. Why does salt remain behind?
A: Method: Evaporation and crystallisation. Water evaporates due to sunlight and leaves dissolved salts behind which crystallise as water concentration increases. Salt remains because it is soluble but non-volatile; when the solvent (water) evaporates, salt cannot vaporise and hence forms crystals.
4Removing Iron from Sand
Case: A science kit contains a mixture of sand and tiny iron filings. The students need to separate the iron.
Q: Which method should they use and explain the principle involved.
A: Use magnetic separation. Hold a magnet close to the mixture; iron filings are attracted to the magnet and separate from sand. This uses the magnetic property of iron—only magnetic materials respond to the magnet while sand does not.
5Oil Spill Cleanup
Case: A small amount of cooking oil fell into a container of water during a cooking class. Students need to separate the two liquids.
Q: Which method is suitable and why? Describe steps briefly.
A: Use a separating funnel or allow the oil and water to stand until they form two layers (oil on top). Then drain the lower water layer using a tap (or spoon out oil). This works because oil and water are immiscible and have different densities, causing layer formation.
6Clothes Drying
Case: After washing, clothes are spread under sunlight and dry within hours.
Q: Which separation process is at work? Explain the process and why clothes dry faster in sunlight.
A: The process is evaporation. Water in the clothes absorbs heat energy and changes into water vapour which disperses into air. Sunlight provides energy that increases evaporation rate, and wind carries away vapour, making drying faster.
7Colored Ink Experiment
Case: A teacher asks students to separate colours in marker ink using paper and a small amount of water.
Q: What method is the teacher demonstrating? Outline the steps and the principle behind it.
A: The teacher demonstrates paper chromatography. Steps: place a dot of ink near one end of filter paper, suspend paper with end in a solvent, let solvent rise carrying components at different rates. Principle: different dye components have different solubilities and affinities for paper, so they travel different distances and separate.
8Separating Rice from Stones
Case: While cooking, Sunita finds small stones mixed with rice grains and needs to remove them quickly.
Q: Which method should she use and why is it effective?
A: Use handpicking. Pick out stones one by one because they are larger and visually different from rice grains. It is effective for mixtures where components are large and easily distinguishable.
9Tea Dust in Sugar
Case: Some tea dust accidentally fell into a jar of sugar. The tea dust is very fine and spreads through the sugar.
Q: Suggest a practical way to separate and recover the sugar. Explain limitations.
A: If tea dust particles are similar in size to sugar, sieving won't work. Add water to dissolve sugar (tea particles are insoluble), filter to remove tea dust (residue), and then evaporate the filtrate to recover sugar crystals. Limitation: evaporation is time-consuming and may cause sugar stickiness; complete recovery may be difficult and flavour may be affected.
10Recovering Spilled Iron Nails
Case: A box with mixed small metal objects (iron nails, brass pins) fell and mixed with sand. You need to recover only the iron nails.
Q: How would you proceed to separate iron nails and why won't the method recover brass pins?
A: Use a magnet to attract iron nails (magnetic separation). Brass is non-magnetic, so it won't be attracted and remains with sand. To recover brass later, other methods like sieving and manual sorting would be needed. Magnetic separation specifically targets ferrous materials.
11Purifying Rainwater
Case: A family collects rainwater in a tank for drinking but wants to purify it before use.
Q: Propose a multi-step purification plan using methods from this chapter and explain the reason for each step.
A: Step 1: Sedimentation to let large dust and particles settle. Step 2: Filtration through sand and gravel to remove finer particles. Step 3: Boiling (or distillation if available) to kill microbes. Optionally use activated charcoal filtration to remove odours or dissolved organics. Each step removes progressively smaller impurities and microbes to make water safe.
12Separating Sugar and Sand
Case: A mixture contains sugar and sand and you need to separate them.
Q: Outline the steps to separate sugar and sand and give observations for each step.
A: Add water to dissolve sugar (observation: solution becomes clear while sand remains undissolved). Filter the mixture (observation: sand remains as residue on filter). Evaporate the filtrate to recover sugar crystals (observation: water gradually disappears and sugar crystals form). This uses solubility, filtration and evaporation/crystallisation.
13Separating Two Liquids
Case: A lab mixture contains oil and water. The teacher wants students to separate them and collect both.
Q: Which apparatus and method will help collect each liquid? Explain briefly.
A: Use a separating funnel. Let the mixture settle into two layers (oil on top, water below). Open the tap to collect the lower water layer first, then collect the oil. This works because the liquids are immiscible and have different densities.
14Recovering Solvent from Solution
Case: You need to recover the solvent (water) from a sugar solution for reuse.
Q: Which method is suitable and why? What would be left in the original container?
A: Use distillation to heat the solution, condense the water vapour and collect it as pure water. The sugar will remain in the original container as it is non-volatile and does not vaporise. Distillation recovers the solvent while leaving solute behind.
15Removing Tea from Milk
Case: A small amount of tea spills into a container of milk and you must separate them (assume small-scale and safe handling).
Q: Is it possible to separate tea from milk? Suggest a practical approach and explain limitations.
A: Tea infuses into milk and forms a mixture with dissolved and suspended components; simple physical separation is difficult. One approach is using filtration to remove any undissolved tea particles, but dissolved colour and flavour remain. Complete separation is not practical; better to discard or use purification methods like distillation which are not suitable for food. Hence, separation is not feasible for restoring original milk quality.
16Industrial Waste Cleanup
Case: A small factory discharges wastewater containing oil droplets and suspended solids.
Q: Recommend a sequence of separation methods to treat the wastewater before disposal and justify each choice.
A: Step 1: Use grit removal/sedimentation to allow heavy particles to settle. Step 2: Skimming or separation to remove oil layers (like using a separator or coalescer). Step 3: Filtration through sand/activated carbon to remove fine particles and organics. Optionally, magnetic separation if metal contaminants are present. This sequence uses gravity, density differences and filtration to progressively clean wastewater.
17Chocolate Processing
Case: In chocolate production, solid cocoa nibs are separated from the shell and later fine particles are filtered out.
Q: Identify at least two separation methods used in this process and explain their role.
A: Methods include winnowing to remove light shells from heavier cocoa nibs (uses air flow and weight difference), and filtration/sieving to remove fine unwanted particles. Winnowing cleans the raw product; sieving ensures uniform particle size for smooth texture in chocolate making.
18School Lab Distillation
Case: A teacher demonstrates distillation to separate alcohol from water using a simple setup and warns students about safety.
Q: Explain the safety precautions that should be followed during distillation and why they matter.
A: Precautions: work under adult supervision, use heat-resistant gloves and goggles, avoid open flames near flammable liquids, secure glassware to prevent tipping, ensure condenser water flow to cool vapour, and keep the area ventilated. These prevent burns, fires and glass breakage, and ensure correct condensation and collection of distillate.
19Filtering Cooking Oil
Case: After frying, reused oil contains food crumbs and needs cleaning for further use.
Q: Which method would you use at home and how effective is it? Mention limitations for long-term reuse.
A: Use filtration through a fine cloth or coffee filter to remove crumbs and particles. It is effective for removing solids but does not remove dissolved oxidation products or degraded compounds formed during frying. Long-term reuse reduces oil quality and may be unhealthy; periodic replacement is recommended.
20Recovering Salt from a Mixture
Case: A mixture contains salt, sand and a magnetic screw. You are asked to recover all three components separately.
Q: Provide a step-by-step separation plan naming each method and the expected observation at each step.
A: Step 1: Magnetic separation to remove the magnetic screw (observation: screw sticks to magnet). Step 2: Add water to dissolve salt (observation: salt dissolves; sand remains). Step 3: Filtration to remove sand as residue (observation: sand on filter paper). Step 4: Evaporation/crystallisation of filtrate to recover salt crystals (observation: water evaporates and salt crystals form). Each step uses magnetic property, solubility, size-based filtration and evaporation respectively.
Case-Based Questions with Answers - CBSE Class 6 Science – Chapter Wise Study Materials Based on NCERT