separation of substances class 6

SEPARATION OF SUBSTANCES-CLASS 6-IMPORTANT TOPICS

separation of substances class 6

In our daily life, there are many instances to separate different substances from a mixture.

We need to separate harmful or non-useful substances. Sometimes, we separate even useful components if we need to use them separately. Different separation methods are used depending upon its state, size, miscibility, etc.

We shall discuss some of the important methods here.

1. HANDPICKING

The method of handpicking is done for separating components having a difference in size. The quantity of substances to be separated should be less.

Example: stones from rice or pulses, husk from wheat.

2. THRESHING

threshing

We can separate the grain from stalks by threshing. By the threshing process, stalks are beaten on a hard surface to free the grains. Bullocks and machines are also used to thresh large quantities of grain.

3.WINNOWING

winnowing

winnowing

Winnowing is used to separate heavier and lighter components of a mixture by wind or by blowing air. Wind manages to separate heavier particles from lighter particles.

We can see winnowing in our paddy fields, where farmers separate lighter husk particles from heavier seeds of grain.

4. SIEVING

sieving

Sieving is done if components of a mixture have different sizes. Smaller particles are allowed to pass through the holes of the sieve while bigger particles will remain on the sieve.

Example: impurities and bran present in flour are removed by sieving, pebbles and stones are removed from sand using sieve at construction sites.

5. SEDIMENTATION, DECANTATION, FILTRATION

filtration

Have you tasted filtered coffee? This is how it is made by the process of filtering.

• Fine insoluble impurities can be removed from liquids by the process of sedimentation, decantation, and filtration.

• When the heavier components in a mixture of solid and liquid settle down at the bottom, that process is called sedimentation.

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  sedimentation
  

• The process of pouring out a clear solution from the top of the mixture after sedimentation is called decantation. 

• The remaining very fine particles can be removed by filtration using a filter paper as shown in the picture. 

• A filter paper has very fine pores and the solid particles in the mixture do not pass through it and remain on the paper.

Example: Mud particles from muddy water can be removed using filter paper.
Cottage cheese or paneer (in Hindi) is filtered through a fine cloth or a strainer.
A similar principle is used for separating a mixture of two liquids that do not mix with each other. For example, oil and water mixture can be allowed to stand for some time to get two separate layers. Then it can be separated by using a separating funnel as shown in the picture.

separating funnel

6. EVAPORATION

salt field

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In this picture, you can see how salt is made from seawater by evaporation in salt fields. To separate water and salt, seawater is evaporated by the heat of the sun. In a few days, the water evaporates completely leaving behind the solid salt. Common salt is then obtained from this after purification.

The process of conversion of liquid into its vapor state is called evaporation.

 CONDENSATION - The process of conversion of any vapor into its liquid form is called condensation. 

We use evaporation and condensation together in the separation of certain mixtures.

 SATURATED AND UNSATURATED SOLUTION

A solution in which no more soluble substance can be dissolved is called a saturated solution.

Example: on adding more salt to the water , it remains undissolved and settles at the bottom. It is a saturated salt solution. A larger quantity of salt can be dissolved on heating. Heating increases the solubility.

If we can add more salt to a solution and if it is getting dissolved completely, it is an unsaturated solution.

  

Here we have discussed a few methods of separation methods only. In higher grades, you will learn more techniques of separation.