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19. Analytical Techniques II Flashcards

1
Q

What is infrared analysis used to identify?

A

the types of bond in a molecule

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2
Q

what are radio waves in NMR used to inform us of?

A

the arrangements of hydrogens in a molecule

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3
Q

what does NMR spectroscopy involve?

A

involves the interaction of materials with the low-energy radio wave region of the electromagnetic spectrum

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4
Q

Wat do the radio waves caused in proton NMR cause the hydrogen nucleus to do?

A

causes the hydrogen nucleus to change its spin state

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5
Q

What is the integration value (intensity of each signal) proportional to in a H NMR spectrum?

A

to the number of equivalent H atoms it represents

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6
Q

How many different groups of hydrogen atoms does ethanol have?

A

3

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7
Q

what is the ratio of equivalent hydrogens in CH3CH(CH3)CH2CH3?

A

6 : 1 : 2 : 3
CH3 (a) CH (b) (CH3) (a) CH2 (c) CH3 (d)

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8
Q

How many signals would CH3 - CO - CH3 have?

A

1 signal

CH3 (a) - CO - CH3 (a)

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9
Q

How many sets of equivalent H’s would CH3CH2COOCH3 have? and its ratio.

A

3 sets of equivalent H’s
ratio = 3 : 2 : 3

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10
Q

How many sets of equivalent H’s would CH3CH(Br)CH2CH3 have? and its ratio.

A

4 sets of equivalent H’s
ratio = 3 : 1 : 2 : 3

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11
Q

In NMR, the samples are dissolved in solvents without any what?

A

without any H1 atoms

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12
Q

What are some examples of solvents used to produce an NMR signal from a sample?

A

CCl4, CDCl3

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13
Q

What does it mean if the solvent does not have any H atoms (NMR)?

A

the solvent wont give any peaks

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14
Q

What type of molecule is CCl4 a good solvent for? why?

A

. for non-polar organic molecules
. because its a non-polar compound

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15
Q

What type of molecule is CDCl3 a good solvent for? why?

A

. for polar organic molecules
. because its a polar covalent molecule

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16
Q

What is TMS full name?

A

Tetramethylsilane

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17
Q

Why is a small amount of TMS added to the sample (NMR)?

A

to calibrate the spectrum

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18
Q

Why is TMS used? (6 things)

A

. its signal is away from all the others
. it only gives one signal
. gives a strong signal so only small amount is needed
. it’s non-toxic
. it’s inert
. it has a low boiling point and so can be removed from sample easily

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19
Q

what is the ppm (chemical shift) a relative scale for (NMR)?

A

how far the frequency of the proton signal has shifted away from that of TMS

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20
Q

what does the chemical shift depend on (NMR)?

A

on what other atoms/ groups are near the H

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21
Q

A more electronegative group gives a ______ chemical shift (NMR)?

A

greater

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22
Q

In high resolution H NMR each signal in the spectrum can be split into further lines dues to what?

A

inequivalent H’s on neighbouring C atoms

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23
Q

The splitting of peak means…. (NMR)?

A

the number of inequivalent H’s on neighbouring C atoms +1

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24
Q

When do nuclei not show coupling amongst themselves?

A

When the nuclei are in identical chemical environments

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25
What is the no. of neighbouring inequivalent H atoms on a singlet?
0
26
What is the no. of neighbouring inequivalent H atoms on a doublet?
1
27
What is the no. of neighbouring inequivalent H atoms on a triplet?
2
28
What is the no. of neighbouring inequivalent H atoms on a quartet?
3
29
What is the no. of neighbouring inequivalent H atoms on a multiplet?
4 +
30
What appearance will CH3-CH2-CO-O-CH3 have (NMR)?
triplet - 3 peaks quartet - 4 peaks singlet - 1 peak
31
Chromatography is an analytical technique that separates components in a mixture between what two phases?
. mobile phase . stationary phase
32
What type of state(s) can a mobile phase be?
liquid or gas
33
What type of state(s) can a stationary phase be?
. solid (as in thin-layer chromatography, TLC)) . or either liquid or solid on a solid on a solid support (as in gas chromatography, GC)
34
What does the separation by column chromatography depend on?
the balance between solubility in the moving phase and retention (act of retaining) in the stationary phase
35
What does a solid stationary phase separate by (chr)?
adsorption
36
What does a liquid stationary phase separate by (chr)?
relative solubility
37
Would polar or non-polar compounds pass through the column quicker if the stationary phase was polar and the moving phase was non-polar (chr)? why?
. the non-polar compounds would pass through the column more quickly than polar compounds . because they would have a greater solubility in the non-polar moving phase
38
What does HPLC stand for?
high performance liquid chromatography
39
When does HPLC occur in the stationary phase?
when it's a solid silica
40
When does HPLC occur in the mobile phase?
a liquid
41
In gas-liquid chromatography GC what state is the mobile phase in?
an inert gas (e.g. N, He, Ar)
42
In gas-liquid chromatography GC what state is the stationary phase in?
a (high b.p.t) liquid (absorbed) on an inert solid
43
What is gas-liquid chromatography used to separate?
separate mixtures of volatile liquids
44
What is the definition of retention time?
the time taken for a particular compound to travel from its injection on the sample to where it leave the column to the detector.
45
What can the retention time be used for?
to identify a substance
46
Why are some compounds not able to be distinguished?
because they have similar retention times
47
What will basic gas-liquid chromatography tell us? (2 things)
. how many components there are in a mixture . the abundance of each substance
48
How does basic gas-liquid chromatography tell us how many components there are in a mixture?
by the number of peaks
49
How does basic gas-liquid chromatography tell us the abundance of each substance?
the area under each peak will be proportional to the abundance of that component
50
How could you enable all the components in a mixture be identified using a gas-liquid chromatography machine?
connect the machine to a mass spectrometer, IR or NMR machine
51
commonly, a mass spectrometer is combined with GC to generate a what?
a mass spectrometer
52
What is GC-MS used in?
analysis, forensics, environmental analysis, airport security and space probes.
53
Write a method for thin-layer chromatography
1. draw a pencil line 1 cm above the bottom of a TLC plate and mark spots for each sample, equally spaced along line 2. use a capillary tube to add a tiny drop of each solution to a different spot and allow the plate to air dry 3. add solvent to a chamber or large beaker with a lid so that is no more than 1cm in depth 4. add the TLC plate into the chamber, making sure that the level of the solvent is below the pencil line. replace the lid to get a tight seal 5. when the solvent reaches about 1cm e) When the level of the solvent reaches about 1 cm from the top of the plate, remove the plate and mark the solvent level with a pencil. Allow the plate to dry in the fume cupboard. 6. Place the plate under a UV lamp in order to see the spots. Draw around them lightly in pencil. 7. Calculate the Rf values of the observed spots.
54
Why is the line in chromatography in pencil?
as it will not dissolve in the solvent
55
Why do we use a tiny drop of each solution in chromatography?
too big a drop will cause different spots to merge
56
Why do we use a 1cm depth of solvent in chromatography?
if solvent is too deep it will dissolve the sample spots from the plate
57
Why do we use a lid (to get a tight seal) in chromatography?
to prevent evaporation of toxic solvent
58
Why do we use a fume cupboard (chr)?
to dry the TLC plate, as the solvent is toxic
59
When is a UV lamp used in chromatography?
if the spots are colourless and not visible
60
If using amino acids, what can be used instead of a UV lamp to locate the spots?
ninhydrin spray
61
How do you calculate the Rf value?
distance moved by amino acid / distance moved by solvent
62
Why wont some substances not separate in TLC?
because similar compounds have similar Rf values. so some spots may contain more than one compound

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