Question

Explain principle, working and applications of Ion Exchange chromatography.

Answer 1

Chromatography-

• Chromatography is a technique of separating two or more dissolved solid which are present in a solution in very small quantity.
• This separation is based on the fact that though two (or more) substances are soluble in the same solvent (say, water) but their solubilities may be different.
• Black ink is a mixture of several coloured substances (or dyes) which can be separated by paper chromatography.

To separate the Dyes Present in Black Ink-

The different coloured dyes present in black ink  can be separated by performing a paper chromatography experiments as follows :

1. Take a thin and long strip of filter paper. Draw a pencil line on it, about 3 centimeters from one end.
2. Put a small drop of black ink on the filter paper strip at the centre of the pencil line.
3. When the drop of ink has dried, the filter paper strip is lowered into a tall glass jar containing some water in its lower part ( keeping the pencil line at the bottom). The filter paper strip is held vertically by attaching its upper end to a glass rod with cello tape (the glass rod being kept over the mouth of glass jar. Please note that through the lower end of the paper strip should dip in water but the pencil line (having dried ink spot on it) should remain above the water level in the jar.
4. The water gradually rises up the filter paper strip by capillary action. As water moves up the paper strip, it takes along the dyes present in ink. The dye which is more soluble in water dissolves first, rises faster and produces a coloured spot at lower heights. In this way, all the dyes present in black ink get separated ( by forming separate different coloured spots).
5. When the water reaches near the top end of the filter paper strip ,the paper strip is removed from the jar and dried. The paper with its separate coloured spots is called a Chromatogram.
6. The chromatogram obtained by using black ink in this experiment has three colourd spot on it. This means that the given sample of black ink has three different dyes mixed in it.

Chromatography is an important tool in chemical analysis. It is used to separate small amounts of dissolved substances. Some of the important applications of chromatography are given below.

• Chromatography are used to separate solutions of coloured substances (dyes and pigments).
• Chromatography is used to forensic science to detect and identify trace amount of substances ( like poisons ) in the content of bladder or stomach.
• Chromatography is used to separate small amount of products of chemical reactions.

Thanks.