Chromatography

Question 1

Stationary phase

Answer 1

Solid substance
Mixture passes over in order to separated

Question 2

Mobile phase

Answer 2

Liquid or gas

Question 3

High affinity to stationary phase

Answer 3

Travel slowly

Question 4

Low affinity to stationary phase

Answer 4

Travel quickly

Question 5

Highly soluble in mobile phase

Answer 5

Travel quickly with solvent

Question 6

Low solubility in mobile phase

Answer 6

Travel slowly with solvent

Question 7

TLC diagram

Answer 7

https://www.chemguide.co.uk/analysis/chromatography/thinlayer.html

Question 8

Stationary phase in TLC

Answer 8

TLC plate
Thin piece of aluminium/glass coated in silica gel

Question 9

Mobile phase in TLC

Answer 9

Solvent/eluant

Question 10

What condition allows spots to become visible in TLC?

Answer 10

UV light/iodine/fluorescent dye

Question 11

RF equation

Answer 11

RF= distance moved by component/distance moved by solvent front

Question 12

Advantage of TLC

Answer 12

Faster than paper chromatography
Works on very small samples

Question 13

Disadvantage of TLC

Answer 13

Similar compounds may have similar Rf values
Cannot be used to separate large quantities

Question 14

Column chromatography uses

Answer 14

Narrow glass tube with spout and tap- column

Question 15

Stationary phase in column chromatography

Answer 15

Column packed with powder such as silica

Question 16

Mobile phase in column chromatography

Answer 16

Solvent/eluant

Question 17

How is the compound separated in column chromatography

Answer 17

Mixture and solvent run through column
Different components of mixture travel through stationary phase and once reached the bottom, can be collected into separate beakers

Question 18

Advantage of column chromatography

Answer 18

Larger quantities can be separated

Question 19

If there is a more polar compound, what would a more polar solvent mean?

Answer 19

Higher solubility to mobile phase
Travels quickly

Question 20

If there is a more polar compound, what would a more polar stationary phase mean?

Answer 20

Higher affinity to stationary phase
Travels slower

Question 21

Gas-liquid chromatography used to

Answer 21

separate complex mixtures of volatile compounds

Question 22

Mobile phase in GC

Answer 22

Carrier gas e.g. nitrogen or helium

Question 23

Stationary phase in GC

Answer 23

Solid/viscous liquid e.g. alkane, which lines the capillary column

Question 24

Why can we only explain separation in terms of affinity to the stationary phase?

Answer 24

Mobile phase is not a solvent

Question 25

How do we record distance travelled with gas chromatography

Answer 25

Retention time- time is takes from point of injection for component to detector

Question 26

Limitation to GC

Answer 26

Lots of chemicals may have similar retention times and peak shapes so cant be positively identified

Question 27

GC-MS

Answer 27

Enables separation of complex mixtures
AND
Identification of each component of that mixture

Question 28

Uses of GC-MS

Answer 28

Forensics
Airport secuirity

Question 29

Why do we wear plastic gloves holding TLC plate?

Answer 29

Essential – to prevent contamination from the hands to the plate

Question 30

Why do we add developing solvent to a depth of not more than 1cm3?

Answer 30

Essential – if the solvent is too deep it will dissolve the mixture from the plate

Question 31

Why do we allow the solvent to rise up the plate to the top?

Answer 31

Not essential – the Rf value can be calculated if the solvent front does not reach the top of the plate

Question 32

Why do we allow the plate to dry in a fume cupboard?

Answer 32

Essential – the solvent is toxic
 

Question 33

Outline the steps needed to locate the positions of the amino acids on the TLC plate and to determine their Rf values.

Answer 33

Spray with developing agent or use UV
Measure distances from initial pencil line to the spots (x)
Measure distance from initial pencil line to solvent front line (y)
Rf value = x / y