thin layer chromatography Flashcards
1
Q
what is chromatography
A
a technique used to separate the components present within a mixture.
2
Q
how does chromatography separate substances
A
by making use of differences in their polarity or molecular size
3
Q
describe separating of substances through the use of thin layer chromatography
A
- uses a fine film of silica or aluminium oxide spread over glass, aluminium foil or plastic
- a small sample of the mixture being tested is spotted onto the base pencil line of the chromatogram
- a solvent dissolves the compounds in the spot and carries the compounds up the chromatogram
- how far the componds are carried depends on how soluble the compounds in the chosen solvent are and how well they adhere to the plate
4
Q
what is normally used to visualise the spots on a chromatogram
A
a developing agent or ultraviolet light
5
Q
what conditions are required to keep the Rf value of a solvent the same
A
- temperature
- solvent
- saturation levels
6
Q
what is TLC used to assess
A
the purity of substances. a pure substance, when spotted and developed ona TLC plate, should appear as a single spot.
7
Q
what does the presence of more than one spot on the chromatogram show
A
that impurities are present
8
Q
how can the identity of a compound be confirmed
A
- by comparing the experimentally determined rf values with a literature or known value determined under the same conditions
- making a direct comparison on a TLC plate between the compound being tested and the pure substance - a co spot could be used
