Chromatography ORGANIC

Question 1

What are the three types of chromatography?

Answer 1

Thin-layer chromatography (TLC)
Column chromatography (CC)
Gas chromatography (GC)

Question 2

What general technique is followed by all types of chromatography?

Answer 2

Components in mixture dissolved in mobile phase flow through stationary phase at varying rates

Question 3

What does the rate of separation depend on in chromatography?

Answer 3

How components in mixture interact with stationary phase and how soluble they are in mobile phase

Question 4

What is the stationary phase in thin-layer chromatography?

Answer 4

Solid silica on plastic/glass plate

Question 5

What is the mobile phase in thin-layer chromatography?

Answer 5

Liquid solvent

Question 6

What is the stationary phase in column chromatography?

Answer 6

Solid silica

Question 7

What is the mobile phase in column chromatography?

Answer 7

Liquid solvent

Question 8

What is the stationary phase in gas-liquid chromatography?

Answer 8

Microscopic liquid film on solid support

Question 9

What is the mobile phase in gas-liquid chromatography?

Answer 9

Inert carrier gas

Question 10

How is Rf value calculated in chromatography?

Answer 10

Rf = distance travelled by component / distance travelled by solvent

Question 11

What is used instead of unique retention factor in GLC?

Answer 11

Retention time

Question 12

How is retention time measured in GLC?

Answer 12

Starts from moment of injection
Ends when component exists chromatography tube

Question 13

What is TLC used for?

Answer 13

Analysing small samples by separation

Question 14

Describe the stationary phase in TLC.

Answer 14

Commonly thin metal sheet coated in alumina or silica
Solute molecules adsorb onto surface

Question 15

Describe the mobile phase in TLC.

Answer 15

Flows over stationary phase
Polar or non-polar solvent that carries components
Polar = water or alcohol
Non-polar = alkanes

Question 16

What can be used to visibily locate sample components in TLC?

Answer 16

UV light
Ninhydrin
Iodine vapour

Question 17

Describe the process of TLC analysis.

Answer 17

Draw baseline on TLC plate in pencil
Spot pure reference compound on left of baseline
Spot sample on right of baseline
Allow to air dry
Place TLC plate in beaker with solvent under spots/baseline and cover with lid
When solvent reaches top, remove from beaker and draw pencil line on solvent front

Question 18

What results are seen in TLC?

Answer 18

The weaker the components interactions with the stationary phase, the further distance moved

Question 19

Why is a reference compound used in TLC?

Answer 19

Rf values compared to identify components of sample

Question 20

What can be used as suitable column in CC?

Answer 20

Vertical glass tube or burette

Question 21

Describe the stationary phase in column chromatography.

Answer 21

Inert solid (powdered silica gel or alumina) placed in column

Question 22

Describe the mobile phase in column chromatography.

Answer 22

A liquid solvent phase added into column until saturated with solvent

Question 23

Describe the process of CC analysis.

Answer 23

Sample dissolved in solvent and added to top of column
More solvent (eluent) added on top
Fresh solvent added as solvent runs to prevent drying out

Question 24

How does sample move in CC? How can it be sped up?

Answer 24

Flows through column via gravity
Sped up by pushing sample and mobile phase through column

Question 25

How is CC sped up in classroom lab?

Answer 25

By attaching gas syringe to column

Question 26

How is CC sped up in industrial lab?

Answer 26

By attaching air line to column

Question 27

What results are seen in CC?

Answer 27

The component with greatest attraction/affinity to stationary phase takes longest time to flow through column

Question 28

How are components identified in CC?

Answer 28

Cololured components identified by Rf value Colourless components identified by fluorescence under UV light and other techniques

Question 29

What is GLC used to analyse?

Answer 29

Gases Volatile liquids Solids in vapour form

Question 30

Describe the stationary phase in CC.

Answer 30

A non-volatile liquid in long coiled clumn

Question 31

Describe the mobile phase in GLC.

Answer 31

An inert carrier gas that moves sample molecules through stationary phase

Question 32

Describe the proces of GLC analysis.

Answer 32

Sample is injected into column through self-sealing disc Vapour formed carried through stationary phase using inert-gas mobile phase

Question 33

How are retention times measured in GLC?

Answer 33

Using detector

Question 34

What are chromatograms used for in GLC?

Answer 34

Recording retention times Each peak represents volatile compound in sample

Question 35

What do relative sizes of peaks in GLC chromatograms represent?

Answer 35

Amount of each compound present in mixture

Question 36

How are unknown molecules identified by GLC?

Answer 36

Retention times on chromatogram are compared with data book values