Practice Questions & Solved Examples

Conceptual Problems

Example 1: The Kitchen Mishap

Problem: While cooking, Rahul accidentally spilled a bowl of green peas into a bucket of wheat flour. How can he separate them back?

Solution: Rahul should use Sieving.

1. Principle: Difference in size.
2. Process: Pour the mixture into a sieve used for flour.
3. Observation: The fine flour will pass through the holes. The large green peas will remain on the sieve.
4. Result: Flour and peas are separated effectively.

Example 2: The Lost Keys

Problem: A carpenter dropped a box of iron nails into a pile of dry leaves. He suggests burning the leaves to get the nails. Is this a good idea? What is a better method?

Solution: No, burning is bad for the environment and might damage the temper of the nails. Better Method: Magnetic Separation.

1. Use a strong magnet attached to a stick.
2. Move it through the pile of leaves.
3. The iron nails will stick to the magnet, leaving the leaves behind.

Example 3: Complex Mixture

Problem: How would you separate a mixture of: Sand, Salt, and Iron filings?

Step-by-Step Solution:

1. Magnetic Separation: Move a magnet over the mixture. The Iron filings will stick to the magnet and are removed.
   • Remaining: Sand + Salt.
2. Sedimentation/Dissolving: Add water to the mixture. Salt is soluble, Sand is not. Stir well.
3. Filtration: Pour the mixture through a filter paper.
   • Residue: Sand stays on the paper.
   • Filtrate: Salt water passes through.
4. Evaporation: Heat the filtrate. Water evaporates (can be collected via condensation if needed).
   • Residue: Salt remains in the container.

Example 4: Lemonade Logic

Problem: Why do we strain lemonade before serving? If we add sugar after adding ice, why does it dissolve slowly?

Solution:

1. Straining: We use a strainer (filtration) to remove lemon seeds (insoluble solid) from the liquid juice.
2. Solubility: Solubility increases with temperature. When ice is added, the water becomes cold, making it harder and slower for the solid sugar to dissolve compared to room temperature water.