Chromatography

Question 1

What is chromatography used for?

Answer 1

It is used to separate individuals of a mixture and subsequently identify them

Question 2

Describe how thin layer chromatography of photosynthetic pigments can be carried out

Answer 2

• crush plant in pestle and mortar and add a solvent e.g. acetone
• draw a pencil line near the bottom of the silica gel
• using a capillary tube, drop sample onto centre of pencil line
• repeat 10 times, allowing for drying inbetween
• place in solvent ensuring line of solvent is below pencil line
• seal chromatogram in jar with solvent
• remove before solvent reaches top of chromatogram

Question 3

What is used to identify substance from a chromatogram?

Answer 3

Rf values

Question 4

How can Rf values be calculated

Answer 4

distance moved by pigment from origin/ distance moved by solvent front from origin

Question 5

What does Rf stand for?

Answer 5

Relative front

Question 6

What affects the rate at which substances move?

Answer 6

• solubility in the solvent used
• size of the molecule
• polarity of the molecule

Question 7

What is the stationary phase in TLC?

Answer 7

Silica gel

Question 8

What is the mobile phased in TLC?

Answer 8

The solvent

Question 9

How can an Rf value be used to identify a substance?

Answer 9

The Rf value of a certain molecule in a certain solvent can be looked up in a table of values and compared

Question 10

How is 2 way chromatography completed?

Answer 10

• normal one way chromatography is run

- the chromatogram is then turned 90 degrees and a different solvent is used

Question 11

Why is 2 way chromatography used?

Answer 11

When substances in the chromatogram have similar Rf values and need further separation