Chromatography is a method used to separate components of a complex mixture in a solution. There are many types of chromatography.
1. Paper chromatography.
2. Column chromatography.
3. Thin-layer chromatography.
4. Gas chromatography.
This can be used to separate components of complexes like leaf extract or black ink. Filter paper is used as the absorbent medium and alcohol is used as a solvent. A drop of the complex (ink or leaf extract) is blotted at a predetermined distance from the edge of the paper. The paper is hung inside a dish containing alcohol (ethanol). As the solvent carries the extract along the paper, the components separate out into different colours. This is because the rates of movement of the different components inside the solvents are not the same.
In chromatography, there are two phases. A stationary phase (filter paper) on which the solutes are adsorbed. A mobile phase (alcohol) which dissolves the solute and carries them.
In column chromatography, a glass tube is used as the column while an adsorbent such as powdered Alumina (Aluminium oxide), magnesium, or calcium trioxocarbonate (IV) is used as the Stationary Phase. A suitable solvent is used as the mobile phase.
The complex mixture in solution is poured down the column (of adsorbent in glass). Then the pure solvent is poured into the column. The components are separated due to their different rates of flow as well as their different rates of adsorption to the column.
Uses/Application of Chromatography
1. In analysing complex mixtures.
2. Identifying the components of petroleum fractions.
3. Monitor the progress of a chemical reaction.
4. Analyze blood and urine samples.
1. What method would you use to separate the following?
(a) Mixture of two solids which have widely different solubilities in water
(b) A mixture of two liquids which have widely different boiling points.
(c) A pure solid from a concentrated solution of its salt
(d) The component colours of leaf
(e) An aqueous solution of Lead (ii) and copper (ii) ionsView Answer
2. (a) What is Sublimation?
(b) Name two substances that can undergo SublimationView Answer
3 (a) Describe how you will separate the components of black ink. Name the process.
(b)Name two other complex mixtures you can separate by the above-named process.View Answer
4. A five-year-old boy was sent to buy salt by his mother, on his way back the salt fell and mixed with sand. As a chemistry student describe the steps you would follow to help the boy get back the salt without buying another one for him.View Answer
5 (a) State one difference between Crystallization and Evaporation to dryness
(b) List two methods that can be used to separate a mixture of Iodine crystal and Iron filings
(c) State one industrial application of (i) Crystallization (ii) ChromatographyView Answer