Questions and Solutions
1. What purpose does handpicking serve in the process of separation?
(ii) Sorting
Explanation: Handpicking is primarily a sorting method used to remove unwanted substances (like stones) from useful ones (like grains) based on visual differences.
2. Which of the following substances are commonly separated using the churning method?
(iii) Cream from milk
Explanation: Churning is used to separate lighter fatty components (butter/cream) from the heavier liquid part of milk or curd.
3. Which factor is usually essential for the filtration?
(iii) Pore size
Explanation: Filtration works because the filter has pores (holes) that allow liquid to pass but block solid particles. If the pore size is too big, the solid will pass through.
4. State with reason(s) whether the following statements are True [T] or False [F]. Correct the False statement(s).
(i) Salt can be separated from salt solution by keeping it under the Sun.
- Answer: [T]
- Reason: The heat from the sun evaporates the water, leaving the salt behind.
(ii) Handpicking should be used only when the quantity of one component is less.
- Answer: [T]
- Reason: It is practically impossible to handpick impurities if they are present in very large quantities or if the total mixture is massive.
(iii) A mixture of puffed rice and rice grains can be separated by threshing.
- Answer: [F]
- Correction: It can be separated by winnowing. Puffed rice is much lighter than rice grains and will blow away. Threshing is for separating grains from stalks.
(iv) A mixture of mustard oil and lemon water can be separated by decantation.
- Answer: [T]
- Reason: Oil and water do not mix (immiscible). Oil forms a separate layer on top of the water, which can be poured off (decanted).
(v) Sieving is used to separate a mixture of rice flour and water.
- Answer: [F]
- Correction: It is separated by filtration or decantation. Wet flour would clog a sieve or pass through with the water. Sieving is for solid-solid mixtures of different sizes.
5. Match the mixtures in Column I with their method of separation in Column II.
| Column I | Column II (Correct Match) |
|---|---|
| (i) Gram flour mixed with black gram | (d) Sieving (Size difference) |
| (ii) Chalk powder mixed with water | (e) Filtration (Insoluble solid in liquid) |
| (iii) Corn mixed with potatoes | (a) Handpicking (Large, visible size difference) |
| (iv) Iron powder mixed with sawdust | (b) Magnetic separation (Magnetic property) |
| (v) Oil mixed with water | (c) Decantation (Immiscible liquids) |
6. In what situations would you use decantation instead of filtration to separate solids from liquids?
Decantation is used when:
- The solid particles are heavy and settle down quickly (sedimentation) at the bottom.
- Absolute purity is not required, and a quick separation is needed (e.g., washing rice).
- A filter is not available.
Filtration is preferred when particles are light/fine and do not settle easily.
7. Can you relate the presence of nasal hair to any separation process?
Yes, nasal hairs act like a filter (Filtration). They trap dust particles and pollutants from the air we breathe, preventing them from entering our lungs, similar to how a sieve or filter paper traps residue.
8. During the COVID-19 pandemic, all of us wore masks. Generally, what material are they made of? What is the role of these masks?
- Material: Masks are generally made of non-woven fabric (like polypropylene) or layers of cotton.
- Role: They act as a filter. They trap respiratory droplets and fine particles containing viruses, preventing them from entering our nose/mouth or spreading to others.
9. A mixture containing potatoes, salt, and sawdust has been given to you. Outline a stepwise procedure for separating each component.
Step 1: Handpicking (Potatoes)
- Potatoes are large solids. Pick them out by hand.
- Result: Potatoes separated. Mixture left: Salt + Sawdust.
Step 2: Dissolving in Water
- Add water to the salt + sawdust mixture.
- Salt dissolves in water. Sawdust is insoluble and floats/suspends.
Step 3: Filtration
- Filter the mixture through a filter paper or cloth.
- Residue: Wet Sawdust stays on the filter.
- Filtrate: Salt solution passes through.
- Dry the sawdust to get it back pure.
Step 4: Evaporation
- Heat the salt solution. Water evaporates.
- Residue: Salt crystals are left behind.
10. ‘Intelligent Leela’ - Fill in the blanks.
Leela was working in the farm with her father when she realised that they left their drinking water at home. Before her father felt thirsty, she went to the nearby pond to fetch some water. After obtaining some water in the container, she noticed that the water was muddy and unfit for drinking. To purify the water, she kept it for some time and then she filtered the muddy water using a piece of muslin cloth. Leela, then, boiled the water for about 10 minutes in a covered pan. After cooling, she filtered it again and made it fit for drinking.
Suggested Title: “Leela’s Water Purification” or “Smart Survival Skills”.