Methods of Separation in Everyday Life — NCERT Solutions

Given: We need to identify situations where decantation is preferred over filtration.

Concept:

• Decantation is the process of gently pouring out the liquid from a container after the heavier insoluble solid has settled at the bottom (sedimentation).
• Filtration uses a filter medium (like filter paper or cloth) to separate insoluble solids from a liquid.

Situations where decantation is preferred:

1. When the solid particles are heavy and settle quickly at the bottom of the liquid — for example, separating sand or mud from water after it has been allowed to stand undisturbed for some time.

2. When the quantity of solid is large and using filter paper would be slow or impractical.

3. When a filter medium is not available — decantation can be done simply by tilting the vessel carefully.

4. When the solid particles are too coarse to require a fine filter — e.g., separating rice from water after washing.

Conclusion: Decantation is preferred when the insoluble solid is heavier and settles at the bottom easily, making it convenient to pour off the liquid without the need for a filter.

Given: We need to relate nasal hair to a method of separation.

Concept: Filtration is the process of separating insoluble solid particles from a liquid (or gas) using a filter that has fine pores.

Relation:

The nasal hair present inside our nose acts as a natural filter. When we breathe in air, the nasal hair traps dust particles, pollen, germs, and other large impurities present in the air. Only clean, filtered air passes through to the lungs.

This is similar to the process of filtration, where a filter medium (here, nasal hair) allows the fluid (air) to pass through while retaining the solid particles (dust, pollen, etc.).

Conclusion: The nasal hair performs the function of filtration — it filters the air we breathe by trapping harmful particles, just as filter paper traps mud particles while allowing water to pass through.

Given: We need to identify the material of masks and explain their role during COVID-19.

Material of Masks:
Masks used during COVID-19 were generally made of:

• Cloth/cotton (for simple reusable masks)
• Non-woven polypropylene fabric (for surgical masks)
• Multiple layers of fine filter material (for N95 masks)

These materials have very fine pores that act as a filter medium.

Role of Masks:

Masks work on the principle of filtration. The fine pores in the mask material:

1. Trap large respiratory droplets containing the COVID-19 virus that are expelled when an infected person coughs, sneezes, or talks.
2. Prevent the wearer from inhaling virus-laden droplets from the surrounding air.
3. Act as a barrier between the nose/mouth and the external environment.

Conclusion: Masks act as filters — they allow air to pass through but block virus-carrying droplets and particles, thereby reducing the spread of COVID-19. This is an application of the filtration method of separation in everyday life.

Given: A mixture of potatoes, salt, and sawdust.

Properties of components:

• Potatoes — large, solid, visible pieces; insoluble in water.
• Salt — fine solid particles; soluble in water.
• Sawdust — fine, light solid particles; insoluble in water; lighter than water (floats).

Step-by-step Separation Procedure:

Step 1: Handpicking — Separate Potatoes

• The potatoes are large in size and can be easily identified and picked out manually from the mixture.
• Result: Potatoes are separated. The remaining mixture contains salt and sawdust.

Step 2: Add Water and Decantation/Filtration — Separate Sawdust

• Add water to the remaining mixture of salt and sawdust.
• Salt dissolves in water to form a salt solution.
• Sawdust, being insoluble and lighter, floats on the surface of the water.
• Carefully decant (pour off) the floating sawdust, or use filtration — pour the mixture through a filter paper. Sawdust will be retained on the filter paper as residue.
• Result: Sawdust is separated. The filtrate is a salt solution (salt dissolved in water).

Step 3: Evaporation — Separate Salt

• Take the salt solution in a china dish.
• Heat it gently so that the water evaporates completely.
• The solid salt is left behind in the china dish.
• Result: Salt is separated.

Summary Table:

Conclusion: By using a combination of handpicking, filtration/decantation, and evaporation, all three components — potatoes, sawdust, and salt — can be successfully separated from the mixture.

Most Appropriate Options (Correct choices are underlined/bold):

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. She served this water to her father while having food, who blessed her and appreciated her efforts.

Reasoning for each choice:

Suggested Title: "Leela's Presence of Mind: Purifying Water the Smart Way"

(Other acceptable titles: "Smart Leela Saves the Day" / "Leela — A Problem Solver")