What is chromatography? How will you separate the components of black ink using chromatography?
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Solution
Chromatography: The technique of separation and purification of the different coloured components of a mixture due to the difference in their extent of solubility in the solvent used for chromatography.
Separating the components of black ink:
A black black ink is a mixture of two or more water soluble coloured components.
The suitable technique to separate the different components of black ink is paper chromatography.
Paper chromatography: When a strip of filter paper is used to carry out chromatography, it is known as paper chromatography.
Principle used in this technique is that the components to be separated are soluble in the same solvent.
Process of paper chromatography:
A thin strip of filter paper is cut out and a line is drawn on it approximately 3 cm above the lower end of the filter paper. This line is called reference line.
A small dot of black ink is placed in the centre of the line drawn.
Once the dot of black ink is dry, it is lowered into the chromatography jar containing water.
The filter paper should be immersed in such a way that the dot of black ink is above the water level in the jar.
The set up should be left undisturbed for some time.
As the water starts to rise up from the lower end of the filter paper, the component of black ink which is more soluble in water rises faster and higher up on the filter paper. The level up to which water rises is known as water front.
Depending on the number of components present in the black ink, some coloured spots are observed corresponding to the separated components of the black ink.
