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Methods of Separation of Substances - Churning

Grade 6CBSE

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

🔑Concepts

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Churning is a method used to separate the components of a mixture by agitating or shaking the liquid mixture vigorously.

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The process is primarily used to separate solid particles that are suspended in a liquid, based on the difference in their densities.

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When a mixture like milk or curd is churned, the lighter components (like butter) move towards the center and surface, while the heavier components (like buttermilk) stay at the bottom or move outwards.

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The principle behind churning is similar to centrifugation, where force is applied to a mixture to separate components of different mass.

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Commonly, in Indian households, a wooden or plastic churner called a 'mathani' is used to extract butter from curd.

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During churning, the lighter particles collect together to form a solid mass that can be easily skimmed off from the liquid.

📐Formulae

Density(ρ)=Mass(m)Volume(V)\text{Density} (\rho) = \frac{\text{Mass} (m)}{\text{Volume} (V)}

Mixture (Curd/Cream)→ChurningButter (Lighter)+Buttermilk (Heavier)\text{Mixture (Curd/Cream)} \xrightarrow{\text{Churning}} \text{Butter (Lighter)} + \text{Buttermilk (Heavier)}

ρbutter<ρbuttermilk\rho_{\text{butter}} < \rho_{\text{buttermilk}}

💡Examples

Problem 1:

Why does butter float on the surface after churning curd?

Solution:

Butter floats because its density is less than that of the buttermilk.

Explanation:

According to the principle of density, if ρ1<ρ2\rho_{1} < \rho_{2}, the substance with density ρ1\rho_{1} will float on the substance with density ρ2\rho_{2}. In this case, since ρbutter<ρbuttermilk\rho_{\text{butter}} < \rho_{\text{buttermilk}}, the butter particles aggregate and rise to the top during agitation.

Problem 2:

Identify the technique used to separate cream from milk in large dairies.

Solution:

Centrifugation (a mechanized form of churning).

Explanation:

In large dairies, milk is rotated at high speeds in a machine. This causes the lighter cream to separate from the heavier milk. The process follows the same logic as manual churning: Agitation→Separation based on Mass\text{Agitation} \rightarrow \text{Separation based on Mass}.