A level OCR Chemistry module 6.3

CHEMISTRY
MODULE 6 – ORGANIC CHEMISTRY AND ANALYSIS
6.3 – ANALYSIS

Chromatography and qualitative analysis

 Describe the process of thin layer chromatography, TLC
o The mobile phase is a liquid solvent (e.g. ethanol)
o The stationary phase is a thin layer of silica gel or
alumina powder on a glass or plastic plate.
o The sample is spotted onto the chromatography plate
o The plate is placed in the solvent which is allowed to
spread up the plate.
o The different substances in the mixture move with the
solvent.
o The distance moved by each substance depends on
how strongly it is adsorbed onto the surface of the
stationary phase




 Explain the term Rf value
o This is represented by Rf value = distance travelled by spot
distance travelled by solvent
o Rf values are constant values for different substances under constant conditions
and can be looked up in a database
o You measure to the vertical center of the spot




 Describe the process of gas chromatography
o Used to separate mixtures of volatile
liquids
o The mobile phase is an unreactive
carrier gas such as nitrogen or
helium
o The stationary phase is a viscous
liquid such as an oil, or a solid which
is packed into a thin tube.
o The sample is injected and vaporized
o The gas mobile phase carries the vapors through the tube


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