Chemistry – Experimental techniques and chemical analysis - Chromatography | e-Consult

Experiment: Separation of Benzene, Toluene, and Xylene by Paper Chromatography

Materials: Chromatography paper, small test tubes, capillary tubes, benzene, toluene, xylene, a suitable solvent (e.g., hexane), a developing agent (e.g., potassium permanganate), a ruler, a beaker or container.

Procedure:

1. A small spot of the mixture (benzene, toluene, and xylene) is applied near the bottom of a strip of chromatography paper.
2. The paper strip is placed in a beaker or container with a small amount of the chosen solvent (e.g., hexane) at the bottom, ensuring the spot is above the solvent level. The beaker is covered to reduce evaporation.
3. As the solvent travels up the paper, it carries the components of the mixture with it.
4. Once the solvent front has reached a suitable height (approximately 2/3 of the way up the paper), the paper is removed from the beaker and allowed to dry.
5. The separated components are visualized using a developing agent, such as potassium permanganate. The paper is sprayed with the potassium permanganate solution.
6. The coloured spots corresponding to benzene, toluene, and xylene will appear at different locations on the paper.
7. The Rf values of each component can be calculated by dividing the distance travelled by the spot by the distance travelled by the solvent front.

Solvent Choice: Hexane is a suitable solvent because it is a non-polar solvent and will dissolve all three components of the mixture. It has a relatively low polarity, which is important for separating these aromatic hydrocarbons. A more polar solvent would not be effective in dissolving the components.

Locating Agent: Potassium permanganate (KMnO4) is a suitable locating agent because it reacts with the aromatic rings of benzene, toluene, and xylene, producing coloured products. The reaction involves oxidation of the aromatic ring. This allows for the visual identification of each component.