3.3.16 - chromatography

Question 1

thin layer chromatography (TLC) allows us too…

Answer 1

separate and identify compounds

Question 2

stationary phase of TLC

Answer 2

silica or alumina mounted on a glass/metal plate
a pencil base line is drawn and drops of mixtures added

Question 3

what is done with stationary phase of TLC

Answer 3

placed in the solvent - the base line must be above the solvent level
leave until solvent has moved up to near the top of the plate
remove, mark the solvent front and allow to dry

Question 4

how does TLC work

Answer 4

works by mixture spots dissolving in the solvent
some chemicals in the mixture may not dissolve as much and stick to the stationary phase quickly
what we are left with is a chromatogram

Question 5

how can we identify chemicals

Answer 5

using their positions on the chromatogram

Question 6

how do we see a colourless compound/ spot on a chromatogram

Answer 6

colourless compounds can be seen using iodine or fluorescent dues and uv light

Question 7

how are fluroscent dyes and uv light used to see colourless compounds

Answer 7

adding a flurosecent dye to silica/alumina can be seen using a uv lamp
the colourless spots on the chromatogram will block any glow from the fluorescent dye
you can then draw round these spots to mark where they are

Question 8

how is iodine used to see colourless compounds

Answer 8

place the chromatogram in a sealed jar with a few iodine crystals
the iodine vapour sticks to the chemicals on the plate dying them purple

Question 9

iodine vapour when using iodine to see colourless compounds is known as a…

Answer 9

locating agent