Activity 1.
Let us consider an example of separating dyes that make up black ink. In this case, water is used as a solvent.
Separating dyes in ink
Procedure
1. Put a small spot of the water-soluble ink onto a strip of filter paper as shown in figure
below
2. Place the filter paper in a beaker of water. Make sure the level of the water is below the
level of the ink spot.
3. Leave the filter paper until the water has risen to the top of the paper.
4. Remove the paper and allow it to dry.
5. Note the colours the ink contains.
level of the ink spot.
3. Leave the filter paper until the water has risen to the top of the paper.
4. Remove the paper and allow it to dry.
5. Note the colours the ink contains.
Observation
Separating the components of black ink by paper chromatography
As the solvent (water) moves up the paper, the dyes are carried with it and begin to separate.
They separate because they have different solubilities in water and are absorbed to different
degrees by the filter (chromatography) paper. As they rise, they are gradually separated.
Separating the components of black ink by paper chromatography
As the solvent (water) moves up the paper, the dyes are carried with it and begin to separate.
They separate because they have different solubilities in water and are absorbed to different
degrees by the filter (chromatography) paper. As they rise, they are gradually separated.
Findings
The different colours of the ink make a pattern of colours formed during the process of
chromatography. This pattern of colours is called a chromatogram.
Figure above shows a chromatogram of black ink. The blue ink has the fastest speed. This means it is the most soluble in water and least absorbed by the paper. The green ink has travelled least.
This means it is the least soluble in water and most absorbed by the paper.
Paper chromatography showing the separated components of black ink.
Activity 2.
An example of this is a water solution of iodine and sodium chloride.
EXPERIMENT:Separating iodine from sodium chloride by solvent extraction.
Method
1. Put the solution into a separating funnel as shown in figure.
2. Add ethoxyethane. This forms a layer on top of the solution (b). The ethoxyethane is
called the extracting solvent.
3. Stopper the separating funnel and shake well figure (c). The iodine, which is more
soluble in the ethoxyethane, passes into the ethoxyethane layer. The sodium chloride remains in the water layer.
4. The water layer is run off into a beaker followed by the ethoxyethane layer into another
beaker (Caution: Remove the stopper before opening the tap).
5. The ethoxyethane is then evaporated off by simple distillation. Similarly, the water layer
can be evaporated to yield sodium chloride.
Method
1. Put the solution into a separating funnel as shown in figure.
2. Add ethoxyethane. This forms a layer on top of the solution (b). The ethoxyethane is
called the extracting solvent.
3. Stopper the separating funnel and shake well figure (c). The iodine, which is more
soluble in the ethoxyethane, passes into the ethoxyethane layer. The sodium chloride remains in the water layer.
4. The water layer is run off into a beaker followed by the ethoxyethane layer into another
beaker (Caution: Remove the stopper before opening the tap).
5. The ethoxyethane is then evaporated off by simple distillation. Similarly, the water layer
can be evaporated to yield sodium chloride.
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