Chapter 33 - Chromatography

Question 1

Define stationary phase

Answer 1

The solid used chromatography (or a liquid supported on a solid)

Question 2

Define mobile phase

Answer 2

The liquid or gas used in chromatography

Question 3

Describe paper/thin layer chromatography

Answer 3

• A pencil is drawn near the bottom of the paper
• A small drop of the mixture is placed on the line
• Solvent is added to just below the line
• Left to stand in a covered beaker
• Different components move up the paper at different rates depending on their relative affinities for the MP or SP

Question 4

Give the Rf equation

Answer 4

Rf = Distance spot moved / Distance solvent moved

Question 5

What if substances separated by paper chromatography are colourless?

Answer 5

Can be revealed using UV light or chemical staining agents such as iodine or ninhydrin

Question 6

Describe column chromatography

Answer 6

• A column is filled with an inert solid (SP)
• Sample mixture introduced at top
• A liquid solvent (eluent) is then applied from the top (MP)
• As the solvent runs down the column the different substances in the mixture will separate out depending on their relative affinities for the MP or SP
• Retention time = time to come out of the bottom of the column

Question 7

Describe gas-liquid chromatography

Answer 7

• Long coiled tube packed with a solid (SP)
• Sample is vapourised and injected into the instrument
• An inert gas (MP) carries the sample through the instrument under pressure and at high temp
• Retention time = time to travel through tube
• Components separated by GC re often analysed by mass spectrometer as they leave tube

Question 8

What advantages does TLC have over paper chromatography?

Answer 8

• It runs faster
• Smaller amounts of mixtures can be seperated
• The spots usually spread out less
• The plates are more robust than paper