Chapter Notes

Methods of Separation in Everyday Life

In our daily lives, we often encounter mixtures of substances that need to be separated. This chapter explores various common methods of separation used to obtain useful components or remove undesirable ones. Just like winnowing separates grains from husk, we can separate different substances based on their properties.

Handpicking

Handpicking is a method of separating solid materials from a mixture by picking them by hand. This method is used when two or more substances are mixed, and the unwanted particles are present in small quantities.

Principle

Handpicking works on the basis of differences in size, colour, and shape of the particles. If the particles to be removed can easily be distinguished and picked by hand, this method is convenient.

Applications

• Separating small stones and husk from grains like wheat and rice.
• Removing whole black peppers or other spices from cooked food like pulao.
• Picking out green chillies from a dish or seeds from a watermelon.
• Sorting different types of flowers.

Threshing

After harvesting, grains are often attached to their stalks. The process of separating the grains from these stalks is called threshing. Traditionally, this was done by beating the stalks.

Winnowing

Winnowing is a method used to separate heavier and lighter components of a mixture.

Principle

This method relies on the difference in weight between the components. When the mixture is exposed to wind or blowing air, the lighter components are blown away, while the heavier components fall more directly.

Process

Traditionally, a soop (bamboo tray) is used. A farmer stands on a raised platform and moves the tray containing threshed grains in the direction of the wind. The lighter husk particles are carried away by the wind, forming a separate pile, while the heavier grains fall closer to the farmer.

Applications

• Separating lighter husk from heavier grains (like wheat or rice) after threshing.
• Separating peanut skins from roasted peanuts by blowing them away.

Sieving

Sieving is a method of separation used for solid-solid mixtures where the components have different sizes.

Principle

A sieve is a device with holes of a specific size. When a mixture is passed through a sieve, the fine particles pass through the holes, while the larger particles are retained on the sieve.

Process

The mixture is placed on the sieve, and the sieve is shaken. Particles smaller than the holes of the sieve pass through, while larger particles remain on top.

Applications

• Separating bran and small stones from wheat flour.
• Separating pebbles and stones from sand at construction sites.
• Separating coconut pieces from rice flour.

Evaporation

Evaporation is a process used to separate a solid that is dissolved in a liquid.

Principle

Evaporation is the process in which a liquid gets converted into its vapour. If a solid is dissolved in a liquid, heating the solution will cause the liquid to evaporate, leaving the solid behind.

Process

To obtain common salt from seawater, for example, seawater is collected in shallow pits and exposed to sunlight and air. The water slowly evaporates due to the sun's heat, leaving behind a solid mixture of salts. Common salt is then purified from this mixture.

Applications

• Obtaining common salt from seawater.
• Separating salt from a salt solution by heating it until all the water boils away, leaving the salt in the container.
• Drying herbs or parts of plants in Ayurveda to remove excess water, leaving the medicinal components.

Sedimentation and Decantation

These methods are used to separate insoluble heavier solids from a liquid.

Sedimentation

Sedimentation is the process where heavier, insoluble components in a liquid settle down at the bottom when the mixture is left undisturbed for some time.

Decantation

Decantation is the process of gently removing the liquid by tilting the vessel after the heavier insoluble solid has settled at the bottom due to sedimentation. The settled solid is called the sediment, and the liquid poured off is the supernatant or decantate.

Applications

• Separating most tea leaves from tea by letting them settle and then pouring the tea.
• Separating oil from water, as oil does not mix with water and forms a separate layer which can then be decanted.
• Separating chalk powder from water.

Filtration

Filtration is a method used to separate insoluble solid components from a liquid using a filter.

Principle

A filter is a material with very small holes or pores that allow the liquid to pass through but retain the solid particles. The size of the pores in the filter determines which particles can pass through.

Process

The mixture is poured through a filter. The liquid that passes through the filter is called the filtrate, and the solid particles retained on the filter are called the residue.

Filter Materials

Various materials can be used as filters, depending on the size of the particles to be removed:

• Tea strainer: Used for larger particles like tea leaves from tea.
• Piece of cloth: Has small pores between woven threads and can be used to filter slightly muddy water.
• Filter paper: Has very fine pores, making it effective for separating even tiny suspended impurities from water.
• Other materials like cotton, charcoal, and sand can also act as filters.

Applications

• Separating tea leaves from prepared tea.
• Purifying muddy water to obtain clear water.
• Fishermen using nets to catch fish, where water drains out through the mesh, is an analogy for filtration.
• Tea bags, originally made of soft cloth and now filter paper, work on the principle of filtration to hold tea leaves while letting water pass.

Churning

Churning is a specific method used to separate components of certain liquid mixtures, particularly to extract butter.

Principle

This method involves vigorously agitating a liquid, often causing lighter components to separate and float to the top.

Process

Curd is churned using a mathni (churner). During churning, the lighter butter separates from the curd and floats to the top, leaving the buttermilk behind.

Applications

• Extracting butter from curd or cream from milk.

Magnetic Separation

Magnetic separation is a method used to separate magnetic substances from non-magnetic substances.

Principle

This method relies on the property of certain materials to be attracted to a magnet. Materials that are attracted to a magnet are called magnetic substances (e.g., iron, nickel, cobalt).

Process

A magnet is moved through a mixture containing magnetic and non-magnetic substances. The magnetic substances get attracted to the magnet and are lifted out of the mixture, leaving the non-magnetic substances behind.

Applications

• Separating iron nails from sawdust.
• Separating iron articles from a heap of waste materials in recycling industries using cranes fitted with powerful magnets.
• Separating scrap iron from waste in manufacturing industries.

Summary

• Handpicking is used for separating solid materials based on differences in size, colour, and shape from a mixture, especially when components are distinct and in small quantities.
• Threshing is the process of beating stalks to separate grains from them.
• Winnowing is the method of separating lighter husk from heavier grains by wind or blowing air.
• Sieving is used to separate solids from a mixture based on variations in particle size using a sieve.
• Evaporation is the process where a liquid converts into its vapour, used to separate a dissolved solid from a liquid.
• Sedimentation is the process of heavier insoluble components settling at the bottom of a liquid.
• Decantation is the process of removing the liquid by tilting the vessel after sedimentation.
• Filtration is used to separate insoluble solid components from a liquid using a filter.
• Churning is employed to extract butter from curd or cream from milk.
• Magnetic separation is the method of separating magnetic and non-magnetic substances using a magnet.