Chromatography and functional group analysis

Question 1

what are the phases in chromotography?

Answer 1

stationary and mobile phase

Question 2

describe the stationary phase

Answer 2

does not move and is usually a solid or a liquid supported on a solid. Area in which material seperates

Question 3

describe the mobile phase

Answer 3

does move and is normally a liquid or a gas. It moves materials, seperating them over the stationary phase.

Question 4

what can chromatography be used for?

Answer 4

the analysis of drugs, plastic, flavourings, air sample and applications in forensic science.

Question 5

what is thin layer chromatography?

Answer 5

a quick and inexpensive analytical technique that indicates how many components are in a mixture. The technique usually uses a TLC plate (plastic sheet or glass) coated with solid adsorbent substance- silica.

Question 6

what is the stationary phase in TLC?

Answer 6

adsorbent

Question 7

what is adsorption?

Answer 7

process by which silica holds different substances in the mixture to its surface

Question 8

how is separation achieved in TLC?

Answer 8

by relative adsorptions of substances with stationary phase. Different components in mixture have different affinities for the absorbent.

Question 9

how do you carry out TLC?

Answer 9

-draw a base line using a pencil about 1cm from the plate end
-spot sample on base line using a capillary tube
-pour solvent into beaker at depth of 0.5cm and place watch glass on top
-place TLC plate in beaker with watch glass on top.
-allow solvent to rise until 1cm below top of plate
-remove plate and immediately mark solvent front with pencil
-circle the invisible and visible spots

Question 10

how do you calculate Rf value?

Answer 10

distance moved by component/ distance moved by solvent front

Question 11

what is gas chromatography used for?

Answer 11

it is useful for separating and identifying volatile organic compounds present in a mixture

Question 12

what is the stationary phase in gas chromatography?

Answer 12

high boiling liquid adsorbed into inert solid support

Question 13

what is the mobile phase in gas chromotography?

Answer 13

inert carrier gas such as helium or neon

Question 14

how does gas chromatography work?

Answer 14

-small amount of volatile mixture is injected into gas chromatograph.
-The mobile carrier gas carries the components in the sample through the capillary column which contains liquid stationary phase absorbed onto the solid support
-the components slow down as they interact with the liquid stationary phase.

Question 15

how are the components in a mixture separated in gas chromotography?

Answer 15

depending on solubility in the liquid stationary phase. The more soluble, the slower it moves through the capillary column.

Question 16

how are compound in a mixture detected in gas chromotography?

Answer 16

components in a mixture reach the detector at different times depending on solubility.

Question 17

what is retention time?

Answer 17

the time taken for each components to travel through the column

Question 18

what two pieces of information can be obtained from a gas chromatogram?

Answer 18

-retention time
-peak integrations

Question 19

what is paper made of?

Answer 19

cellulose

Question 20

what is the mobile phase in paper chromatography?

Answer 20

solvent

Question 21

what is the stationary phase in paper chromatography?

Answer 21

water molecules

Question 22

how are components separated in paper chromatography?

Answer 22

dependent on relative solubility. If the sample is more soluble in the mobile phase, it moves up. If more soluble in the stationary phase, it will stay towards the bottom

Question 23

how do you identify compounds using chromatography?

Answer 23

by comparing Rf values to a database

Question 24

how can you detect invisible solutes?

Answer 24

-use UV light
-spray with ninhydrin. When sprayed, the spots will turn purple.

Question 25

what are the disadvantages of paper chromatography?

Answer 25

-unknown compounds have no reference on database
-similar compounds have similar Rf values
-difficult to find a solvent that separates all compounds in a mixture

Question 26

what is the chemical test and observation for an alkene?

Answer 26

test: add bromine
observation: orange to colourless

Question 27

what is the chemical test and observation for an haloalkane?

Answer 27

test: add silver nitrate and ethanol and warm to 50 degrees in a water bath
observation: choloroalkane- white precipitate
bromoalkane- cream precipitate
iodoalkane- yellow precipitate

Question 28

what is the chemical test and observation for a carbonyl?

Answer 28

test: add 2,4-DNP
observation: orange precipitate

Question 29

what is the chemical test and observation for an aldehyde?

Answer 29

test: add Tollens reagent and warm
observation: silver mirror

Question 30

what is the chemical test and observation for a primary and secondary alcohol and aldehyde?

Answer 30

test: add acidified potassium dichromate (VI) and warm in a water bath
observation: orange to green

Question 31

what is the chemical test and observation for a carboxylic acid?

Answer 31

test: add aqueous sodium carbonate
observation: effervescene

Question 32

how do you identify a phenol?

Answer 32

-phenols are acidic compounds which can be tested using pH indicator paper
-phenols are not as acidic as carboxylic acids and do not react with sodium carbonate
-phenol undergoes an electrophilic addition reaction with bromine at room temperature. Bromine decolorises and a white precipitate is formed