NCERT SCIENCE-CLASS 9-SEPARATION TECHNIQUES , IS MATTER AROUND US PURE-PART-2

IS MATTER AROUND US PURE? - PART-2 SEPARATION OF MIXTURES

In the first part, we have discussed element, compound, types of solution and mixtures. In this session, we shall discuss the various methods to separate the components of a mixture.

NCERT SCIENCE-CLASS 9-SEPARATION TECHNIQUES, IS MATTER AROUND US PURE-PART-2

Is matter around us pure? Substances which we see around us may not be pure always. In many instances, we have to separate the components present in a mixture. So we are using several separation techniques, In the case of a heterogeneous mixture, components can be separated by simple methods like handpicking, sieving, filtering, magnetic separation etc. 

In this session, we can see other methods of separation used in a homogeneous mixture and some special cases of heterogeneous mixtures.

1. Evaporation 

The evaporation process is used for separating sea salt from seawater, which you have studied in lower grades. The same process can be used for separating the volatile component (solvent) from its non- volatile solute.

INK

Example: Ink is a mixture of dye. To obtain dye particles from ink, few drops of ink can be heated on a watch glass. It should not be heated directly. By keeping the watch glass over a beaker containing water and by heating the beaker ink particles are obtained as a residue. You can refer to the diagram given in your textbook.

2. Centrifugation

How can we separate butter from buttermilk? You might have seen churner used for this purpose. Still, we are using churner to collect butter and we make ghee from it.

When the solid particles present in a liquid is very small in size, it will pass through the filter paper. Those mixtures can be separated by the separation techniques called centrifugation. 

CENTRIFUGE

The principle of centrifugation is that the denser particles are forced to the bottom of the centrifuging tube and the lighter component in the mixture will remain on top when it is spun at high speed.

Using this principle we can:

• separate butter from curd
• test blood and urine in the diagnostic lab
• squeeze out water from wet clothes in a washing machine.

3. Separating funnel

How can we separate oil from a mixture of oil and water? Two immiscible liquids can be separated based on its densities. The apparatus used for this separation technique is called separating funnel. By opening the stopcock of the separating funnel, we can pour out the lower layer carefully.

SEPARATING FUNNEL

4. Sublimation

How can we separate a white coloured ammonium chloride from a similar coloured common salt? The sublimation process can be used to separate a mixture containing a component which sublimes from a component which does not sublimes.

Ammonium chloride will undergo sublimation on heating, while common salt does not. On cooling it further, ammonium chloride will undergo deposition and it can be separated.

There are many other compounds like naphthalene and anthracene which can be separated by this method.

5. Chromatography

It is the separation technique for separating solutes that dissolve in the same solvent. This technique got its name from the Greek word Kroma which means colour. It was used for the separation of colours in dyes earlier. Using advanced technology, now we are using it in various fields like separating drugs from the blood.

DYE

A dye is a mixture of two or more colours mixed together. By chromatography, the coloured component that is more soluble in the water rises faster and gets separated. So depending upon the solubility different coloured components are seen on different zones.

6. Distillation

DISTILLATION

This is a very popular separation technique. Distillation is the method used to separate components of a mixture containing two miscible liquids that boil without decomposition. Each component should have sufficient difference in boiling point and it should be more than 25 K.The basic principles behind this is evaporation followed by condensation. The component which boils first will get evaporated first and is collected after condensing it.

Example: a mixture of acetone and water.

DISTILLATION

For mixtures with less than 25 K boiling point difference, fractional distillation is used. It is widely used in petroleum refineries to separate fractions of petroleum-like petrol, diesel, kerosene etc. Components of petroleum and different gases present in the air are separated by an advanced separation technique called fractional distillation.

fractional distillation

7. Crystallisation

Have you ever wondered how crystals are formed? Do you know how these beautiful crystals are made? 

Crystallisation is a method usually used to purify solids. It separates a pure solid component in the form of crystals from its solution leaving behind the impurities in it.

Example: Pure copper sulphate can be obtained from its impure sample by crystallisation. Salt from seawater is also purified by this method.

crystals

crystals

So depending upon the nature of the components present in a mixture, we can select various methods of separation. These separation technique has got much application in the manufacturing field of many substances.