To separate such mixtures that contain a sublimable volatile component from a non-sublimable impurity (salt in this case), the sublimation process is used . Some examples of solids which sublime are ammonium chloride, camphor, naphthalene and anthracene.
Is the dye in black ink a single colour?
Take a thin strip of filter paper.
Draw a line on it using a pencil, approximately 3 cm above the lower edge
Put a small drop of ink (water soluble, that is, from a sketch pen or fountain pen) at the centre of the line. Let it dry.
Lower the filter paper into a jar/glass/beaker/test tube containing water so that the drop of ink on the paper is just above the water level, as shown in Fig.4 (b) and leave it undisturbed.
Watch carefully, as the water rises up on the filter paper. Record your observations.
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.
This process of separation of components of a mixture is known as chromatography. Kroma in Greek means colour. This technique was first used for separation of colours, so this name was given.
Chromatography is the technique used for separation of those solutes that dissolve in the same solvent.
With the advancement in technology, newer techniques of chromatography have been developed. You will study about chromatography in higher classes.
- colours in a dye
- pigments from natural colours
- drugs from blood
How can we separate a mixture of two miscible liquids?
Let us try to separate acetone and water from their mixture.
Take the mixture in a distillation flask. Fit it with a thermometer.
Arrange the apparatus as shown in Fig.
Heat the mixture slowly keeping a close watch at the thermometer.
The acetone vaporizes, condenses in the condenser and can be collected from the condenser outlet.
Water is left behind in the distillation flask.
This method is called distillation. It 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.