6.3 analysis Flashcards
what are the 2 phases of chromatography?
stationary and mobile phases
what kind of chemical will move more in a non-polar solvent during chromatography?
a non-polar chemical
what kind of chemical will move more in a polar solvent during chromatography?
a polar chemical
in TLC what is the stationary and mobile phase?
paper = stationary solvent = mobile
how do you calculate Rf value?
how far chemical moved/how far solvent moved
in gas chromatography, what is the mobile and stationary phase?
gas = mobile liquid = stationary
describe how gas chromatography works in separating more soluble and least soluble compounds
more soluble compounds move the fastest and reach the detector first
in gas chromatography, what is the time taken to reach the detector called?
retention time
what does the area under each peak represent in gas chromatography?
area under peak links to concentration
bigger area = more concentrated
how can unknown concentrations be found from a gas chromatogram
putting known concentrations through the chromatogram will form a peak area of known concentration which you can compare to unknown peak areas
which other analytical technique can be paired with gas chromatography to identify the compounds in a sample?
mass spec
give two problems associated with chromatography
- similar compounds have similar retention times or Rf values
- new compounds cannot be identified in a database
how do impurities affect melting point?
LOWER melting point
how do impurities affect boiling point?
INCREASE boiling point
outline the test for unsaturation/alkenes
bromine water - add a few drop of br water to sample and shake
if it decolourises, it is unsaturated or an alkene
outline the test for haloalkanes
aqueous silver nitrate and ethanol AgX precipitate forms then halogen can be inferred from colour white - cl cream - br yellow - i
outline the test for carbonyls
brady’s reagent - orange precipitate forms
outline the test for aldehydes
tollen’s - silver mirror
acidified potassium dichromate - orange to green
outline the test for carboxylic acids
- using pH probe or universal indicator - check ph is that of weak acid
- react with effervescence with metal carbonates
outline the test for phenol
- pH probe/universal indicator - pH should be a weak acid
- no reaction with carbonate ion
what does NMR stand for and how does it work?
nuclear magnetic resonance
measures how radio waves interact
what three things can proton NMR tell you
the distinct hydrogen environments
relative number of hydrogens in each environment
number of hydrogens on adjacent carbons
what’s the splitting rule for proton NMR peaks?
peaks are split into n+1 peaks where n=number of hydrogens on adjacent hydrogens
what do you call a peak that is split into 1 2 3 4 >5 many peaks?
singlet doublet triplet quartet multiplet
what are 4 rules for OH and NH groups in proton NMR spec?
- they can appear anywhere on the spectrum
- they do not get split
- they do not cause splits
- they are always singlets
what can you use to distinguish the OH and NH peaks from the other peaks in proton NMR?
run dueterium oxide D₂O (isotope hydrogen)
the singlets caused by OH and NH should disappear, the remaining singlets are CH environments
