RP12 - Chromatography

Question 1

Describe the process for TLC

Answer 1

Wearing gloves, draw a pencil line 1 cm above the bottom of a TLC plate and mark spots for each sample, equally spaced along
line.

Use a capillary tube to add a tiny drop of each solution to a different spot

Add solvent to a chamber or large beaker with a lid so that is no more than 1cm in depth

Place the TLC plate into the chamber, making sure that the level of the solvent is below the pencil line.

Replace the lid to get a tight seal.

When the level of the solvent reaches about 1 cm from the top of the plate, remove the plate and mark the solvent level with a pencil.

Allow the plate to dry in the fume cupboard.

Place the plate under a UV lamp in order to see the spots. Draw around them lightly in pencil.

Calculate the Rf values of the observed spots.

Question 2

Why is the base line drawn in pencil

Answer 2

Pencil will not dissolve in the solvent

Question 3

Why is the depth of the solvent only 1cm^3

Answer 3

If the solvent is too deep it will dissolve the sample spots from the plate

Question 4

Why is a lid placed on the beaker

Answer 4

Prevents evaporation of toxic solvent

Question 5

Why is a UV lamp used

Answer 5

If the spots are colourless and not visible, it allows them to be seen

Question 6

Rf =

Answer 6

Distance moved by spot / Distance moved by solvent

Question 7

If the stationary phase was polar and the moving phase was non-polar would polar or non-polar compounds move faster

Answer 7

Non-polar compounds as they have a greater solubility in the non-polar moving phase

Question 8

What does a solid stationary phase separate by

Answer 8

Adsorption

Question 9

What does a liquid stationary phase separate by

Answer 9

Relative solubility