Thin Layer Chromatography

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Experiment 5
Title : Thin Layer Chromatography
Objectives:
i. To distinguish polar and non-polar solvents. ii. To familiar with the analysis technique by using the thin layer chromatography. iii. To differentiate the retention factor, Rf for different compounds.
[pic]
Result:
|Compound |Distance traveled by the compound |
|o-nitroanaline |2.45 |
|p-nitroaniline |1.70 |
|Unknown sample |2.45 |

Calculation:

The Rf value for each dye is then worked out using the formula:
[pic]

o-nitroanaline:

Rf = 2.45 3.00 = 0.82

p-nitroaniline:

Rf = 1.75 3.00 = 0.58

Unknown sample:

Rf = 2.45 3.00 = 0.82

Discussion:

Silica gel is a form of silicon dioxide (silica). The silicon atoms are joined via oxygen atoms in a giant covalent structure. However, at the surface of the silica gel, the silicon atoms are attached to -OH groups.
So, at the surface of the silica gel you have Si-O-H bonds instead of Si-O-Si bonds. The diagram shows a small part of the silica surface.
[pic]
The surface of the silica gel is very polar and, because of the -OH groups, can form hydrogen bonds with suitable compounds around it as well as van der Waals dispersion forces and dipole-dipole attractions.
As the solvent begins to soak up the plate, it first dissolves the compounds in the spot that you have put on the base line. The compounds present will then tend to get carried up the chromatography plate as the solvent continues to move upwards.
How fast the compounds get carried up the plate depends on two things: • How soluble the compound is in the solvent. This



References: Jim Clark (2007). Thin Layer Chromatography. Retrieved on September 30, 2010 from http://www.chemguide.co.uk/analysis/thinlayerchromatography Thin Layer Chromatography

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