6.3 analysis

Question 1

what are the 2 phases of chromatography?

Answer 1

stationary and mobile phases

Question 2

what kind of chemical will move more in a non-polar solvent during chromatography?

Answer 2

a non-polar chemical

Question 3

what kind of chemical will move more in a polar solvent during chromatography?

Answer 3

a polar chemical

Question 4

in TLC what is the stationary and mobile phase?

Answer 4

paper = stationary 
solvent = mobile

Question 5

how do you calculate Rf value?

Answer 5

how far chemical moved/how far solvent moved

Question 6

in gas chromatography, what is the mobile and stationary phase?

Answer 6

gas = mobile
liquid = stationary

Question 7

describe how gas chromatography works in separating more soluble and least soluble compounds

Answer 7

more soluble compounds move the fastest and reach the detector first

Question 8

in gas chromatography, what is the time taken to reach the detector called?

Answer 8

retention time

Question 9

what does the area under each peak represent in gas chromatography?

Answer 9

area under peak links to concentration

bigger area = more concentrated

Question 10

how can unknown concentrations be found from a gas chromatogram

Answer 10

putting known concentrations through the chromatogram will form a peak area of known concentration which you can compare to unknown peak areas

Question 11

which other analytical technique can be paired with gas chromatography to identify the compounds in a sample?

Answer 11

mass spec

Question 12

give two problems associated with chromatography

Answer 12

• similar compounds have similar retention times or Rf values
• new compounds cannot be identified in a database

Question 13

how do impurities affect melting point?

Answer 13

LOWER melting point

Question 14

how do impurities affect boiling point?

Answer 14

INCREASE boiling point

Question 15

outline the test for unsaturation/alkenes

Answer 15

bromine water - add a few drop of br water to sample and shake
if it decolourises, it is unsaturated or an alkene

Question 16

outline the test for haloalkanes

Answer 16

aqueous silver nitrate and ethanol 
AgX precipitate forms then halogen can be inferred from colour
white - cl
cream - br
yellow - i

Question 17

outline the test for carbonyls

Answer 17

brady’s reagent - orange precipitate forms

Question 18

outline the test for aldehydes

Answer 18

tollen’s - silver mirror

acidified potassium dichromate - orange to green

Question 19

outline the test for carboxylic acids

Answer 19

• using pH probe or universal indicator - check ph is that of weak acid
• react with effervescence with metal carbonates

Question 20

outline the test for phenol

Answer 20

• pH probe/universal indicator - pH should be a weak acid

- no reaction with carbonate ion

Question 21

what does NMR stand for and how does it work?

Answer 21

nuclear magnetic resonance

measures how radio waves interact

Question 22

what three things can proton NMR tell you

Answer 22

the distinct hydrogen environments
relative number of hydrogens in each environment
number of hydrogens on adjacent carbons

Question 23

what’s the splitting rule for proton NMR peaks?

Answer 23

peaks are split into n+1 peaks where n=number of hydrogens on adjacent hydrogens

Question 24

what do you call a peak that is split into 
1
2
3
4
>5
many peaks?

Answer 24

singlet
doublet
triplet
quartet
multiplet

Question 25

what are 4 rules for OH and NH groups in proton NMR spec?

Answer 25

• they can appear anywhere on the spectrum
• they do not get split
• they do not cause splits
• they are always singlets

Question 26

what can you use to distinguish the OH and NH peaks from the other peaks in proton NMR?

Answer 26

run dueterium oxide D₂O (isotope hydrogen)

the singlets caused by OH and NH should disappear, the remaining singlets are CH environments