Name the appropriate methods to separate the following mixtures :
(a) Cream from milk
(b) Dyes from black ink
(c) Oxygen from the air
(d) Pigments from leaf extract
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Solution
Different separation techniques are present depending upon the properties of the substances to be separated
(a) For the separation of cream from milk we can use the centrifugation technique.
The particles which can not separate using ordinary filter is separated using this method.
The milk (mixture) which is taken in a centrifuge tube rotated using a centrifugal machine.
During this centrifugation method, denser particles are allowed to move bottom, and lighter particles are allowed to move up.
Milk is a colloidal solution, to separate cream from milk we can use this technique.
(b) To separate dyes from black ink, we can use chromatography. i.e.., paper chromatography.
Chromatography involves the movement of the mobile phase through the stationary phase.
The sample which is dissolved in a solvent act as the mobile phase and the stationary phase can be paper (paper chromatography), silica (column chromatography), etc.
To separate dyes from black ink, we can take paper chromatography.
Initially we can take a chromatographic paper which is 20 cm long and 5 cm wide.
From one end of the paper taking 4 cm gap,we can make a line using a pencil (baseline).
Then place drop of black ink at the middle of the baseline and let it dry .
Suspend this set up in a jar containing (water) solvent by touching the paper strip in solvent but not the baseline.
Close the jar.
After rising the solvent through the paper, the colors blue, red, and yellow separate out into different heights depending upon the solubility on solvent and on their ability to adhere to the paper.
In this way, we can separate the dyes from black ink.
(c) To separate oxygen from the air we can use fractional distillation
We know that air is a mixture of different gases, to separate the components first we have to liquefy the air.
The liquid air is then heated and allowed to pass through a fractionating column.
The different gases present in air separated depending upon the boiling points into different heights.
(c) Pigments from leaf extract can be separated using chromatography.
First of all we can take a chromatographic paper which is 20 cm long and 5 cm wide.
From one end of the paper taking 4 cm gap,we can make a line using a pencil (baseline).
Grind the leaves, add acetone or methanol and then filter it (leaf exctract ready).
Place a drop of leaf extract on middle of the baseline.
Suspend the paper in a jar containing (20 ml petroleum ether and chloroform) solvent by touching the paper strip in solvent but not the baseline.
Close the jar.
After rising the solvent through the paper, pigments will separate out i.e chlorophyll b, chlorophyll a, xanthophyll, and carotene.
