thin layer chromatography

Question 1

what is chromatography

Answer 1

a technique used to separate the components present within a mixture.

Question 2

how does chromatography separate substances

Answer 2

by making use of differences in their polarity or molecular size

Question 3

describe separating of substances through the use of thin layer chromatography

Answer 3

• 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

Question 4

what is normally used to visualise the spots on a chromatogram

Answer 4

a developing agent or ultraviolet light

Question 5

what conditions are required to keep the Rf value of a solvent the same

Answer 5

• temperature
• solvent
• saturation levels

Question 6

what is TLC used to assess

Answer 6

the purity of substances. a pure substance, when spotted and developed ona TLC plate, should appear as a single spot.

Question 7

what does the presence of more than one spot on the chromatogram show

Answer 7

that impurities are present

Question 8

how can the identity of a compound be confirmed

Answer 8

• 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