Simple chromatography

Question 1

the stationary phase in paper chromatography is

Answer 1

the liquid or solid that does not move

in other words the water trapped in the fibres of the chromatography paper

Question 2

the mobile phase is

Answer 2

the liquid that moves through the stationary phase and transports the components
in other words, the solvent

Question 3

chromatography is used to

Answer 3

• to separate a mixture into its individual components

- to identify the components of a mixture by considering how far they have travelled up the paper

Question 4

chromatography is a good way of

Answer 4

checking how pure a synthesised organic compound is

Question 5

all forms of paper chromatography need the following:

Answer 5

• a container (usually glass) with a lid. the lid is there to prevent evaporation of the solvent. the container could be a beaker or a rectangular tank
• paper, specially formulated chromatography paper gives better results. a method to support the paper in the container is also necessary
• a solvent, in some cases, water works well, but often the solvent is a mixture organic compounds and is chosen to fir the characteristics of the components of the mixture

Question 6

a component that is strongly attracted to the stationary phase but …………… attracted to the mobile phase will……………

Answer 6

but weakly attracted to the mobile phase will not travel very far up the paper

Question 7

a component that is weakly attracted to the stationary phase but …………… attracted to the mobile phase will …………………………

Answer 7

but strongly attracted to the mobile phase will travel a long way up the paper

Question 8

we can use chromatography on organic substances if we

Answer 8

if we spray the organic substances with a chemical reagent that will react to give a visible colour or by using ultraviolet radiation

Question 9

Thin layer chromatography, (TLC) is when

Answer 9

a sheet of glass or plastic coated in a thin layer of silica or alumina is used instead of paper

Question 10

the distance travelled by the solvent is

Answer 10

the distance between the base line and the solvent front

Question 11

the Rf value is calculated by:

Answer 11

Rf = distance travelled by component / distance travelled by solvent

Question 12

Rf stands for

Answer 12

‘retardation (sometimes ‘retention’) factor’

Question 13

Rf values depend on

Answer 13

the solvent used

Question 14

column chromatography is when

Answer 14

a tube (e.g. a burette) is packed with a stationary phase (silica or alumina) which is soaked in a solvent.
the mixture to be tested in then placed on top of the stationary phase and more solvent (the mobile phase) is added on top.
when the tap is opened, the solvent drips through and the components of the mixture separate as they move down.
more solvent is added from the top and eventually one component can be collected in a container

Question 15

the advantage of column chromatography is

Answer 15

that much larger quantities of material can be separated than with paper chromatography

Question 16

Rf stands for

Answer 16

Retention factor