ORGANIC CHEMISTRY- chromatography

Question 1

what are the basic principles of all kinds of chromatography?

Answer 1

A mixture is separated if it is dissolved in a solvent and this mobile phase is passed over a solid ( the stationary phase)

Question 2

what is the mobile phase?

Answer 2

carries the soluble components of the mixture

Question 3

what relationship between a sample and the mobile phase makes the sample move faster?

Answer 3

components with more affinity to the solvent move faster

Question 4

what does the stationary phase do?

Answer 4

Holds back components of the mixture that are attracted to it.

Question 5

what is the relationship between a sample and the stationary phase that make the sample move slower?

Answer 5

more affinity for the stationary phase means the component moves slower, often attracted by hydrogen bonding

Question 6

how are substances separated by chromatography?

Answer 6

each component have different affinities to the stationary and mobile phases so they move at different rates and are separated over time.

Question 7

why will different substances show different Rf values?

Answer 7

they are bonded differently and have different polarities
- more polar bonds = more retention time/ smaller rf value since hydrogen bonds are attracted more strongly to the stationary phase.

Question 8

what is the stationary phase in TLC?

Answer 8

plate coated in silica SiO2

Question 9

what are the advantages of TLC over paper chromatography?

Answer 9

runs faster
smaller amounts of mixture can be separated
TLC plates more robust than paper

Question 10

how can you observe colourless spots?

Answer 10

shine UV light on them
spray with ninhydrin (amino acids from colourless to purple)

Question 11

what does rf value stand for?

Answer 11

retention factor - measure of the rate of movement of a component

Question 12

how could you confirm the identity of a substance from its Rf value?

Answer 12

compare your rf value to accepted rf values for that substance

Question 13

what is column chromatography?

Answer 13

column packed with silica and has solvent run through it downwards

Question 14

stationary phase in column chromatography?

Answer 14

silica packed into a column

Question 15

mobile phase in chromatography?

Answer 15

solvent added at top and runs down
called “eluent”

Question 16

advantages of column chromatography?

Answer 16

more than one eluent can be used which leads to better separation
large amounts can be separated and collected after separation

Question 17

what is the stationary phase in gas-liquid chromatography?

Answer 17

powder coated with oil packed into long thin capillary tube. Coiled and placed in oven.

Question 18

mobile phase in gas-liquid chromatography?

Answer 18

carrier inert gas eg He

Question 19

what do you measure in gas-liquid chromatography?

Answer 19

retention time = diff components of the mixture takes different amounts of time to move through

Question 20

advantages of GLC?

Answer 20

GC- can detect minute traces of substances

Question 21

uses of GLC

Answer 21

test athletes blood and urine for drugs

Question 22

How can you use GC or GCMS to identify substances?

Answer 22

match gas chromatograph to that of a known substance under the same conditions = retention time should exactly match.

substances identity can be confirmed by mass spectrometry, NMR or IR spectroscopy.

Question 23

how does GCMS work?

Answer 23

gas chromatography is run = retention time recorded.
Mixture run through Mass spectrometer = fragmentation pattern confirms identity.

Question 24

will alcohol or aldehyde have a shortest retention time by column chromatography?

Answer 24

Aldehyde has shortest retention time = has less polar bond than alcohol so adsorbs less to stationary phase, moving down column quicker rate.