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Chromatography is widely used in chemistry as a separation technique - Leaving Cert Chemistry - Question 2 - 2008
Question 2
Chromatography is widely used in chemistry as a separation technique. (a) Describe, with the aid of clearly labelled diagrams, how you would set up and carry out an... show full transcript
Worked Solution & Example Answer:Chromatography is widely used in chemistry as a separation technique - Leaving Cert Chemistry - Question 2 - 2008
Step 1
Describe, with the aid of clearly labelled diagrams, how you would set up and carry out an experiment to separate the components in a mixture of indicators using paper chromatography, thin-layer chromatography or column chromatography.
Answer
Paper Chromatography
- Setup: Draw a line about 2 cm from the bottom of the chromatography paper. Use a capillary tube to spot the mixture of indicators on the line.
- Elution: Place the paper in a beaker containing a suitable solvent, ensuring the solvent level is below the line.
- Separation: As the solvent moves up, it carries the components of the mixture with it, separating them based on their affinities for the paper and the solvent.
Thin-Layer Chromatography
- Setup: Apply the mixture using a capillary tube onto a thin-layer chromatography plate, marking it approximately 2 cm from the bottom.
- Place in Tank: Place the plate in a tank with the eluent, ensuring that the solvent level is below the sample line.
- Elution: The solvent moves up the plate, separating the components based on their interaction with the stationary phase (the plate) and the mobile phase (the solvent).
Column Chromatography
- Dissolve Mixture: Dissolve the mixture in an eluent and pour it into the column.
- Add Eluent: Continuously add eluent to the column, allowing it to flow through and carry the mixture.
- Separation: As different components interact with the stationary phase in the column, they will travel at different rates and separate accordingly.
Step 2
Explain why the different components of the mixture travel different distances along the paper in thin-layer or through the column in a given time.
Answer
The different components travel different distances because of their varying affinities for the stationary phase (the paper or the column material) and the mobile phase (the solvent). Components that are more soluble in the solvent will travel farther, while those that adhere more strongly to the stationary phase will travel less. This leads to a separation of components based on their chemical properties.
Step 3
Step 4
Step 5
Explain the function of the tube labelled X.
Answer
The tube labelled X serves to allow the steam to enter the distillation apparatus. It helps facilitate the transfer of steam, which assists in carrying the volatile organic compounds away from the plant material during the distillation process.
Step 6
Describe a brief technique that could be used to separate the organic substance from the water.
Answer
A simple technique to separate the organic substance from the water is using a separating funnel. The mixture can be poured into the funnel, and upon settling, the denser water can be drained from the bottom, leaving the organic compound at the top.
Step 7