Class 9 Separating the components of a mixture, How can we obtain different gases from air?

Topics to be covered

`=>` Separating the components of a mixture
`=>` How can we obtain different gases from air?

๐’๐ž๐ฉ๐š๐ซ๐š๐ญ๐ข๐ง๐  ๐ญ๐ก๐ž ๐‚๐จ๐ฆ๐ฉ๐จ๐ง๐ž๐ง๐ญ๐ฌ ๐จ๐Ÿ ๐š ๐Œ๐ข๐ฑ๐ญ๐ฎ๐ซ๐ž

`color{green}("๐Ÿ ๐„๐•๐€๐๐Ž๐‘๐€๐“๐ˆ๐Ž๐:")` Using evaporation method ,the volatile component (solvent) from its non-volatile solute by the method of evaporation.


Due to evaporation method we can easily obtain the constituents of ink (mixture of dye and water).

`color{green}("๐Ÿ ๐‚๐„๐๐“๐‘๐ˆ๐…๐”๐†๐€๐“๐ˆ๐Ž๐ :")` It is a method for the separation of suspended particles of a substance from a liquid in which the mixture is rotated at high speed in a centrifuge machine.


The principle is that the denser particles are forced to the bottom and the lighter particles stay at the top when spun rapidly. So the liquid being lighter will remain on the top and using this we can separate the cream from the milk.


`color{green}(โ€ข)` Used in diagnostic laboratories for blood and urine tests.

`color{green}(โ€ข)` Used in dairies and home to separate butter from cream.

`color{green}(โ€ข)` Used in washing machines to squeeze out water from wet clothes.

`color{green}("๐Ÿ‘ ๐’๐„๐๐€๐‘๐€๐“๐ˆ๐Ž๐ ๐Ž๐… ๐“๐–๐Ž ๐ˆ๐Œ๐Œ๐ˆ๐’๐‚๐ˆ๐๐‹๐„ ๐‹๐ˆ๐๐”๐ˆ๐ƒ๐’")`

The principle is that immiscible liquids separate out in layers depending on their densities.


Kerosene oil has lesser density as compared to that of water so it settles to the top of water and water can therefore be obtained first from the bottom by opening the stopcock of the funnel.

`color{green}("๐Ÿ’ ๐’๐”๐๐‹๐ˆ๐Œ๐€๐“๐ˆ๐Ž๐:")` Mixtures that contain a sublimable volatile component can be separated from a non-sublimable impurity (salt in this case) using the sublimation process. Some examples of solids which sublime are ammonium chloride, camphor, naphthalene and anthracene.

`color{green}("๐Ÿ“ ๐‚๐‡๐‘๐Ž๐Œ๐€๐“๐Ž๐†๐‘๐€๐๐‡๐˜:")` Chromatography(Kroma in Greek means colour ) is the technique used for separation of those solutes that dissolve in the same solvent. This technique was first used for separation of colours, so this name was given.

The ink that we use has water as the solvent and the dye is soluble in it. As the water rises on the filter paper it takes along with it the dye particles.
Usually, a dye is a mixture of two or more colours. The coloured component that is more soluble in water, rises faster and in this way the colours get separated.

`color{red}("๐€๐ฉ๐ฉ๐ฅ๐ข๐œ๐š๐ญ๐ข๐จ๐ง๐ฌ :")`

Chromatography is used to separate

`color{green}(โ€ข)` colours in a dye

`color{green}(โ€ข)` pigments from natural colours

`color{green}(โ€ข)` drugs from blood

`color{green}("๐Ÿ” ๐’๐„๐๐€๐‘๐€๐“๐ˆ๐Ž๐ ๐Ž๐… ๐Œ๐ˆ๐—๐“๐”๐‘๐„ ๐Ž๐… ๐“๐–๐Ž ๐Œ๐ˆ๐’๐‚๐ˆ๐๐‹๐„ ๐‹๐ˆ๐๐”๐ˆ๐ƒ๐’:")`

Distillation is used for the separation of components of a mixture containing two miscible liquids that boil without decomposition and have sufficient difference in their boiling points.

`color{green}("๐…๐‘๐€๐‚๐“๐ˆ๐Ž๐๐€๐‹ ๐ƒ๐ˆ๐’๐“๐ˆ๐‹๐‹๐€๐“๐ˆ๐Ž๐")`

Now for the separation of a mixture of two or more miscible liquids having the difference in boiling points less than 25 K, fractional distillation process is used, for example, for the separation of different gases from air, different factions from petroleum products etc. The apparatus is similar to that for simple distillation, except that a fractionating column is fitted in between the distillation flask and the condenser.

`color{green}("๐Ÿ• ๐‚๐‘๐˜๐’๐“๐€๐‹๐‹๐ˆ๐’๐€๐“๐ˆ๐Ž๐")`

Crystallisation is a process that separates a pure solid in the form of its crystals from a solution.

Crystallisation technique is better than simple evaporation technique as โ€“

`color{green}(โ€ข)` some solids decompose or some, like sugar, may get charred on heating to dryness.

`color{green}(โ€ข)` some impurities may remain dissolved in the solution even after filtration. On evaporation these contaminate the solid.


`color{green}(โ€ข)` Purification of salt that we get from sea water.

`color{green}(โ€ข)` Separation of crystals of alum (phitkari) from impure samples.

In cities, drinking water is supplied from water works. A flow diagram of a typical water works is shown in Fig. 2.13.

๐‡๐Ž๐– ๐‚๐€๐ ๐–๐„ ๐Ž๐๐“๐€๐ˆ๐ ๐ƒ๐ˆ๐…๐…๐„๐‘๐„๐๐“ ๐†๐€๐’๐„๐’ ๐…๐‘๐Ž๐Œ ๐€๐ˆ๐‘ ?

Air is a homogeneous mixture and can be separated into its components by fractional distillation.

`color{green}(โ€ข)` Liquid air can be obtained by increasing the pressure and decreasing temperature.

`color{green}(โ€ข)` This liquid air is then allowed to warm-up slowly in a fractional distillation column, where gases get separated at different heights depending upon their boiling points.