Separation of Substances | Class 6 | Chapter 5 | Bharti Bhawan | NCERT | CBSE NOTES

Separation of Substances 

Science Notes

Class 6

 

Mixture :- Mixture is the substance  that can separate into two or more substances by simple physical means.

 

Components :- The pure substances that make up a mixture are called the components or the constituent of the mixture.

Mixture on the basis of State of Constituents

Solid Mixture                    Mixture of two or more solids

Liquid Mixture                  Mixture of two or more liquids

Gaseous Mixture             Mixture of two or more gases

 

Solid-liquid mixture         Mixture of two or more solids and liquids

Liquid-gas mixture          Mixture of two or more liquids and gases 

 

Mixture

Usually Classified on the basis of the state of the constituent.

Homogeneous Mixture :- A mixture in which solute and solvent are mixed uniformly. In this mixture solute completely dissolved or mix in solvent and becomes disappear.

Ex.- mixture of water and salt.                    

Heterogeneous Mixture:- A mixture in which the components of the mixture are not uniform. In this mixture solute can't mix or partialy mix in solvent and can be seen easily.

Ex.- Mixture of sand and Water.

Type	Homogeneous	Heterogeneous
Solid	All alloy Stainless Steal	Rice + Stone, Salad, Chalk + Sugar
Liquid	Solution of spirit in water	Oil + Water
Gaseous	Air (Mixture of all gases)	-
Solid – Liquid	Solution of salt in water	Sand + Water
Solid – Gas	-	Smoke (Soot + Air)
Liquid – Gas	Air dissolved in water, Fizzy drink (CO2 dissolved in water)	Mist (droplets of water + Air)

 

Why Separation

        ·         To remove undesirable constituents.

        ·         To obtain desirable substances.

        ·         To obtain highly pure substances.

Methods of Separation

        1.       Hand-Picking

        2.       Winnowing

        3.       Sieving

        4.       Magnetic Separating

        5.       Sedimentation and Decantation

        6.       Filtration

        7.       Churning

        8.       Evaporation

        9.       Distillation

       10.    Dissolution and Evaporation

 Separation of Mixture 

Hand-Picking

If a constituent of a solid mixture is big and visibly different.

Ex:- Separating Stone from rice

Science Notes Class 6

1. Matter and it's Nature

2. Food

3. Classification of Material

4. Clothes and Fibre 

5. Separation of Substances

6. Study Of Changes

Winnowing

When one constituent is light and another is heavy.

Ex:- Separating Chaff (the covering of grain) from grain

Sieving

When particle size of constituents are different.

Ex.- Separating stone from sand.

Magnetic Separation

If a constituent of a mixture contains iron substance.

Ex.- Separation of scrap iron from scrap yard.

Sedimentation and Decantation

Ex :- Process of removing water from the mixture of and sand water (Sedimentation)

Sedimentation :-

Sedimentation is a physical water treatment process using gravity to remove suspended solids from water.

Decantation :-

Decantation is the process of separation of liquid from solid and other immiscible (non-mixing) liquids, by removing the liquid layer at the top from the layer of solid or liquid below.

 

Loading :- When  we use some other particle too load the impurity (alum is used to load  the mud in  muddy water) which help the impure particles to  sink.

Immiscible liquid :-  It can also be separated by decantation, otherwise we use separate funnel.

Filtration

Filtration is the better option than decantation to separate liquid from an insoluble solid.

 

Filtration in the laboratory :- A circular paper is folded along its diameter into two semicircles. It is once again folded into four quarter-circles. Now a cone is opened by holding three quarter-circles on one side. This cone is fitted into the cone of a funnel and moistened with water so that the filter paper adheres to the funnel.

  The funnel is fitted to a stand and a beaker is placed below in such a way that the stem of the funnel touches the wall of the beaker. The supernatant liquid is slowly poured along a glass rod into the funnel. The solid collects on the filter paper, whereas the liquid passes through. The clear liquid thus obtained is called filtrate.

 

Mixture of sand and water or Chalk and water can be separated by filtration.

 

Filtration at Home:- Filtration is done at home using a strainer or a piece of cloth.

Churning

 

Process of obtaining creams from milk. In washing machine, the dirt separates from the cloth by a similar action.

Evaporation

A solid can be recovered from its solution by evaporating the solvent.

Separating salt/sugar and water.

Distillation

In this process a homogeneous or heterogeneous mixture of liquid and solid can be separated.

A liquid is vaporised by being boiled, and the vapours are condensed and collected separately. If the liquid were mixed with any solids, the solids would not vaporise. Thus, a liquid can be separated from a solid mixed with it.

Experiment:-  Separation of water and salt from Sugar Syrup.

 A solution of salt or sugar is taken in the flask. The flask is heated gently so that the liquid boils. In no time, water starts collecting in the test tube. The water thus collected does not have the taste of salt or sugar, it is pure and is called distilled water.

On distillation for some time, all the water is distilled out and a white residue of the salt or sugar is left in the flask.

That’s how the distilled water is prepared for laboratory or medical purpose.

Dissolution and Evaporation

This method is useful when one constituent of a solid mixture is soluble in a solvent and the other is not.

Experiment:- Separating the mixture of Salt and Sand.

Take a mixture of salt and sand in a beaker. Add some water to the mixture and stir it vigorously. Warm it from time to time so that all the salt dissolves in the water. Heating helps dissolution. Filter, and wash the residue 4-5 times with hot water. Evaporate the filtrate to dryness in a china dish. You will obtain a white solid which is salt. The residue on the filter paper is sand, which can be dried in the sun.

Crystallisation:- While evaporating a solution, a stage comes when the amount of solvent becomes very little or become Concentrated Solution, and after allowing it to cool slowly, crystals of the substance dissolved start separating. The process is called Crystallisation.

Or

The process of separating a dissolved substance in the form of crystals from a mixture is called crystallisation.

It is used to obtain a substance in the pure state.

 Type of Mixture and method of separations

Type of mixture and method	When applicable	Example
Solid liquid mixtures
1.       Sedimentation and Decantation	When the mixture is heterogeneous	Separating sand or chalk from water
2.       Filtration	”	”
3.       Churning	When the mixture is homogeneous	Separating cream from milk
4.       Distillation	When the mixture is homogeneous or heterogeneous	Separating water form salt or sugar
Liquid mixtures
1.       Decantation	When the liquids are immiscible	Separating oil form water
2.       Using a separating funnel	”	”

 

Experiment

How is common salt obtained from sea water?

Sea water is collected in shallow pits dug on the seashore. The heat of the sun makes the water evaporate. When enough water has evaporated, the Sea water or salt solution becomes concentrated. Then the salt begins to crystallise. The salt is further purified and mixed with a chemical called sodium iodate. This mixture is iodised table salt. Sodium iodate contains iodine. (lack of iodine – goitre)

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