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Methods of Separation of Substances - Handpicking, Winnowing, and Sieving

Grade 6CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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A mixture contains two or more substances mixed together in any proportion. Separation is necessary to remove undesirable substances or to obtain useful components.

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Handpicking: This method is used for separating slightly larger-sized impurities like pieces of dirt, stones, and husk from wheat, rice, or pulses. It is effective when the quantity of impurities is not very large.

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Winnowing: This method is used to separate heavier and lighter components of a mixture by wind or by blowing air. It is commonly used by farmers to separate lighter husk particles from heavier seeds of grain.

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Sieving: This process allows the fine particles to pass through the holes of the sieve while the bigger impurities remain on the sieve. It is used when components of a mixture have different sizes.

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The choice of separation method depends on the physical properties of the components, such as their size (ss), mass (mm), or state of matter.

📐Formulae

Total Mass of Mixture=∑i=1nmi\text{Total Mass of Mixture} = \sum_{i=1}^{n} m_i

Condition for Winnowing: mgrain≫mhusk\text{Condition for Winnowing: } m_{\text{grain}} \gg m_{\text{husk}}

Condition for Sieving: dparticle<dpore\text{Condition for Sieving: } d_{\text{particle}} < d_{\text{pore}}

Efficiency of Separation (%)=(mrecoveredmtotal)×100\text{Efficiency of Separation (\%)} = \left( \frac{m_{\text{recovered}}}{m_{\text{total}}} \right) \times 100

💡Examples

Problem 1:

A construction worker needs to separate small pebbles from a heap of sand. Which method should be used?

Solution:

Sieving.

Explanation:

Since the pebbles and sand particles differ significantly in size (dpebble>dsandd_{\text{pebble}} > d_{\text{sand}}), a sieve with a mesh size smaller than the pebbles but larger than the sand particles will allow the sand to pass through while retaining the pebbles.

Problem 2:

How can a farmer separate dried stalks and husk from wheat grains after harvesting?

Solution:

Winnowing.

Explanation:

Wheat grains are much heavier than the dried husk. When the mixture is allowed to fall from a height in the presence of wind, the lighter husk is carried away by the air, while the heavier grains fall almost vertically to form a separate heap.

Problem 3:

While preparing to cook, a chef notices a few small stones in a bowl of 1 kg1\text{ kg} of pulses. Which method is most practical here?

Solution:

Handpicking.

Explanation:

Because the stones are few in number, have a different color or shape, and are large enough to be seen and held by fingers, they can be easily removed manually from the pulses.