33 chromatography

Question 1

what is chromatography?

Answer 1

separation techniques

Question 2

what are the 3 things needed for every type of chromatography?

Answer 2

1. stationary phase
2. mobile phase
3. mixture of 2 or more substances that need to be separated

Question 3

what is a stationary phase?

Answer 3

solid substance that the mixture passses over

Question 4

what is a mobile phase?

Answer 4

liquid or gas that is carried over the stationary phase

Question 5

what are the mixtures separated due to?

Answer 5

different affinities to the stationary phase or differences in solubility

Question 6

what happens if a component of the mixture has a high affinity to the stationary phase?

Answer 6

will travel slowly

Question 7

what happens if a component of the mixture has a low affinity to the stationary phase?

Answer 7

will travel quickly

Question 8

what happens if a component of a mixture is highly soluble?

Answer 8

will travel quickly with the solvent

Question 9

what happens if a component of a mixture has low solubility?

Answer 9

will travel slowly with the solvent

Question 10

what are 3 types of chromatography?

Answer 10

1. thin layer chromatography (TLC)
2. column chromatography
3. gas liquid chromatography (GC)

Question 11

what is the stationary phase in TLC?

Answer 11

thin piece of aluminium or glass coated in silica gel or aluminia

Question 12

what is the mobile phase in TLC?

Answer 12

solvent

Question 13

how is the mixture separated in TLC?

Answer 13

1. mixture dropped at the bottom of the stationary phase
2. once separated and dry, examined under UV light/chemical reagents

Question 14

describe the solubility and affinity for a component in TLC that has travelled further up

Answer 14

higher solubility
lower affinity to the stationary phase

Question 15

describe the solubility and affinity for a component in TLC that has travelled lower down

Answer 15

lower solubility
higher affinity to the stationary phase

Question 16

how can you identify the components in TLC?

Answer 16

by calculating Rf value

Question 17

what does Rf value shhow?

Answer 17

how far a component has moved compared to the solvent front

Question 18

what is the equation for Rf value?

Answer 18

distance moved by component/distance moved by solvent

Question 19

what are 3 advantages for TLC?

Answer 19

• faster than paper chromatography
• works on small samples
• determines when a chemical reaction is complete

Question 20

what are 5 limitations for TLC?

Answer 20

• similar compounds can have similar Rf values
• conditions have to be the same to compare Rf values
• new compounds have no reference Rf values
• can be difficult to find a solvent that separates all components
• can’t be used to separate large quantities

Question 21

what is the stationary phase in column chromatography?

Answer 21

powder (silica or aluminia)

Question 22

where is the stationary phase in column chromatography?

Answer 22

in a narrow glass tube with taps and spouts called a column

Question 23

how is the mixture separated in column chromatography?

Answer 23

1. mixture loaded onto the top of the column
2. a solvent is poured onto the top
3. different components collected at the bottom in separate beakers at different rates

Question 24

what is the mobile phase in column chromatography?

Answer 24

solvent

Question 25

what is an advantage of column chromatography?

Answer 25

larger quantities can be separated