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Module 6
Chapter 29
PMT flashcards chapter 29
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Cards (51)
What is chromatography?
A family of
separation
techniques
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What principle does chromatography depend on?
Mixtures are separated when dissolved in a
solvent
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What is the mobile phase in chromatography?
It carries the soluble components of the
mixture
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What relationship makes a sample move faster in chromatography?
More
soluble
components move faster
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What does the stationary phase do in chromatography?
It holds back components attracted to it
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What relationship makes a sample move slower in chromatography?
More affinity for the
stationary phase
means slower movement
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What kind of bonding often slows down a sample in chromatography?
Often involves
hydrogen bonding
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How are substances separated by chromatography?
Different
affinities
for
mobile
and
stationary
phases
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Why do different substances show different Rf values?
They have different
polarities
and
bonding
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What does TLC stand for?
Thin Layer Chromatography
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What is the stationary phase in TLC?
Coated sheet of
silica
or
alumina
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What are the advantages of TLC over paper chromatography?
Runs
faster
Smaller
amounts
can be
separated
TLC
plates
are more
robust
than
paper
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How can you observe colourless spots in chromatography?
Shine
UV
light or use a
developing agent
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How do you calculate the Rf value?
Rf =
distance moved by spot
/
distance moved by solvent front
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What does Rf value stand for?
Retention factor
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How can you confirm the identity of a substance from its Rf value?
Compare Rf value to
accepted values
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What is the stationary phase in gas-liquid chromatography?
Powder coated with oil in a
capillary tube
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What is the mobile phase in gas-liquid chromatography?
Carrier gas
, inert like
N2
or
He
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What do you measure in gas-liquid chromatography?
Retention time
of components
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What are the advantages of GLC?
Very sensitive to
minute
traces of substances
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What are GLC’s uses?
Testing blood and urine for
drugs
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How can you use GC or GCMS to identify substances?
Match
retention time
to known substances
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How does GCMS work?
Run GC, record
retention time
, then use MS
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How do you test for alkenes and what is the result?
Shake with
bromine
water;
decolourised
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How do you test for haloalkanes and what is the result?
Add
NaOH
, acidify, add
AgNO3
; precipitate forms
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How do you test for alcohols and what is the result?
Add
acidified K2Cr2O7
;
orange to green
change
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How do you test for aldehydes and what are the results?
Warm with
Fehling’s
;
brick red
ppt forms
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How do you test for carboxylic acids and what is the result?
Add
Na2CO3
;
CO2
gas given off
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How do you test for phenols?
Neutralisation reaction with
NaOH
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How do you test for carbonyl compounds?
React with
2,4-DNP
;
orange precipitate
forms
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What does NMR stand for?
Nuclear Magnetic Resonance
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What are the basic principles of NMR?
It uses
magnetic fields
and radio waves to analyze
nuclei
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How does NMR determine the structure of complex molecules?
By placing them in a
magnetic field
and applying
EM waves
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What happens to nuclei in NMR when the right frequency of radio waves is absorbed?
The nuclei flip from
parallel
to
anti-parallel
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What is one use of NMR?
MRI
scans
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What kind of nuclei does NMR work with?
Nuclei with an uneven number of
nucleons
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What do the following indicate for 13C NMR: Number of signals, Chemical shift, Area under peak, Splitting?
Number of signals: One for each
carbon environment
Chemical shift: Greater indicates different environments
Area under peak:
Proportional to
number of carbon atoms
Splitting: Not applicable for 13C NMR
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Why is it easier to get a spectrum of 1H NMR than 13C NMR?
1H is more
abundant
than 13C
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What peaks would you expect to see for H NMR on a low resolution spectrum?
One peak for each set of
inequivalent
H atoms
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What does the area under the peak represent for H NMR?
It is proportional to the number of
1H
atoms
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