Methods of Separation in Everyday Life — NCERT Solutions, AI Tutor & Practice

Understand: A mixture contains two or more substances that are physically combined.

Analyse: We separate substances for several reasons:

1. To remove harmful or useless components — e.g., removing small stones and husk from grains before cooking.
2. To obtain a useful component — e.g., separating cream (malai) from milk to make butter.
3. To remove impurities — e.g., filtering tea leaves out of prepared tea.

Conclude: We separate mixtures to make substances safe, pure, or useful for our needs.

Understand: Winnowing is a method of separating heavier and lighter components of a mixture using wind or blowing air.

Analyse: When the mixture (such as grain and husk) is dropped from a height:

• The lighter husk is carried away by the wind and falls a little distance away.
• The heavier grains fall straight down and collect in a heap.

Conclude: Winnowing is used by farmers to separate light husk and chaff from heavier grain seeds after threshing.

Understand: Sieving separates components of a mixture that differ in size, using a sieve with small holes.

Analyse:

• The smaller particles pass through the holes of the sieve.
• The larger particles remain on top of the sieve.

Example: While making flour dough, we sieve wheat flour so that fine flour passes through and larger bran particles or impurities stay behind.

Conclude: Sieving is useful when the particles to be separated have clearly different sizes.

Understand: Handpicking is the method of separating substances by simply picking them out by hand.

Analyse: It is suitable when:

• The quantity of impurity is small.
• The impurity is large enough to be seen and picked, e.g., stones, husk pieces, or insects in rice, wheat, or pulses.

Example: Removing small stones and dirt particles from a bowl of dal before cooking.

Conclude: Handpicking works only when the components differ in size or colour and the unwanted matter is present in small amounts.

Understand: Filtration is a method to separate insoluble solid particles from a liquid using a filter (such as filter paper, cloth, or a sieve).

Analyse:

• The liquid (called the filtrate) passes through the fine pores of the filter.
• The insoluble solid particles are too large to pass and stay on the filter (called the residue).

Example: Straining tea to separate the tea leaves, or filtering muddy water to remove mud particles.

Conclude: Filtration works only when the solid is insoluble in the liquid.

Understand: Salt is dissolved in seawater, so it cannot be filtered out. We use evaporation.

Analyse:

1. Seawater is collected in shallow pits or pans.
2. The Sun's heat causes the water to evaporate (turn into vapour and escape into the air).
3. As water leaves, the salt is left behind as solid crystals.

Conclude: Evaporation separates a dissolved solid from a liquid. This is how salt is obtained from seawater in coastal salt pans.

Understand:

• Sedimentation: The process in which heavier insoluble particles settle down at the bottom of a container when the mixture is left undisturbed. The settled matter is called sediment.
• Decantation: Gently pouring out the clear liquid from the top without disturbing the settled sediment.

Analyse (cleaning muddy water):

1. Muddy water is left undisturbed → mud particles settle at the bottom (sedimentation).
2. The clear water on top is gently poured out into another container (decantation).

Conclude: Sedimentation followed by decantation gives us cleaner water, though it may still need filtration for finer particles.

Understand: Salt dissolves in water; sand does not. We combine several methods.

Analyse — steps:

1. Add water to the mixture and stir. Salt dissolves, sand remains undissolved.
2. Filter the mixture. Sand stays as residue on the filter; salt solution passes through as filtrate.
3. Dry the sand collected on the filter.
4. Evaporate the salt solution using heat. Water escapes as vapour, and solid salt is left behind.

Conclude: Sand is recovered by filtration and salt by evaporation — this shows how multiple methods can be combined.

Understand: Threshing is the process of separating grain seeds from the harvested stalks of a crop.

Analyse:

• Farmers beat the stalks or use machines/animals to loosen the grains from the stalk and husk.
• This produces a mixture of grain, husk, and small chaff.
• Winnowing is done afterwards to separate the lighter husk from the heavier grain using wind.

Conclude: Threshing must come first because the grains have to be freed from the plant before winnowing can separate them from the husk.

Understand: When a solid like sugar or salt is added to water, it dissolves to form a solution.

Analyse:

• A given amount of water can dissolve only a limited quantity of a solid.
• If we keep adding the solid, a stage comes when no more of it dissolves and it settles at the bottom.
• Such a solution is called a saturated solution.
• Adding more water provides more space for particles to dissolve, so the extra solid dissolves again.

Conclude: A saturated solution is one in which no more solute can dissolve at a given temperature; increasing water raises how much solid can be dissolved.

Analyse each mixture:

| Mixture | Method | Reason | |---|---|---| | (a) Tea leaves from tea | Filtration | Leaves are insoluble solids strained from the liquid | | (b) Stones from wheat | Handpicking | Stones are few and large enough to pick | | (c) Butter from curd | Churning | Lighter fat separates as butter when churned | | (d) Husk from wheat | Winnowing | Light husk is blown away, heavier grain falls down |

Conclude: The right method depends on differences in size, weight, solubility, or density of the components.

Understand: Evaporation is the process by which a liquid changes into vapour (gas) on heating.

Analyse:

• When a salt solution is heated, the water gains enough energy to escape as water vapour into the air.
• Salt does not evaporate at these temperatures — it needs a much higher temperature to change state.
• So the water leaves the container, but the salt remains behind as solid crystals.

Conclude: Water escapes into the air as vapour while salt, being non-volatile at that temperature, stays back — which is why evaporation successfully separates the dissolved salt.