unit 4 - how to pass: chromatography Flashcards
What is chromatography?
A technique used to separate the components present within a mixture.
What does chromatography do?
It separates substances by making use of differences in their polarity or molecular size.
What does TLC use?
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 line of the chromatogram. A solvent dissolves the compounds in the sport and carries the compounds up the chromatogram.
What does how far the compounds are carried depend on?
How soluble they are in the chosen solvent and how well they adhere to the plate.
What is usually required to visualise the spots on the chromatogram?
A developing agent or ultraviolet light.
How can Rf values be calculated?
Using the forula: Rf = distance travelled by the sample/distance travelled by the solvent.
When does a compound always have the same Rf value?
Under the same conditions (temperature, solvent and saturation levels)
How can the indentity of the compound be confirmed?
By comparing the experimentally determined Rf value with a literature or known value determined under the same conditions.
How can a compound also be confirmed?
By making a direct comparison on a TLC plate between the compound being tested and the pure substance.
What is TLB used for?
To assess the purity of substances.
How should a pure substance, when spotted and developed on a TLC, appear as?
A single sport (some impurities may not be visible by TLC analysis).
What shows that impurities are present?
The presence of more than one spot.
