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Alevel Chemistry Edexcel > Topic 19 - Modern Analytical Techniques 2 > Flashcards

Topic 19 - Modern Analytical Techniques 2 Flashcards

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1
Q

What is high resolution mass spectrometry?

A

mass spectrometry which can measure Mr to 4 decimal places (more accurate)

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2
Q

What can high resolution mass spectrometry be used for?

A

to distinguish between compounds that appear to have same Mr when rounded to a whole number

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3
Q

What does NMR stand for?

A

nuclear magnetic resonance

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4
Q

What is NMR (nuclear magnetic resonance)?

A

an analytical technique which uses a magnetic field to align protons in the nucleus of hydrogen atoms and carbon-13 atoms
-is used to determine structure of a compound

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5
Q

What is used as a standard in NMR?

A

tetramethylsilane (TMS)

(CH3)4Si

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6
Q

Why is TMS used as a standard/comparative peak in NMR?

A
  • all 12 of its hydrogen atoms are in the same environment (no splitting pattern)
  • all of its hydrogen atoms are more heavily shielded in any other molecule (aka their e- lie closer to the hydrogens than in any other molecule)
  • it is inert
  • its peak is to the right so doesn’t overlap with other peaks
  • it has a low boiling temperature/is volatile so can be easily removed
  • gives a strong signal so only a small amount needed
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7
Q

What does C-13 NMR provide information about?

A

position of C-13 atoms in a molecule

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8
Q

What does proton NMR provide information about?

A

positions of H atoms in a molecle

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9
Q

What does low resolution NMR tell us?

A
  • number of hydrogen environments

- number of hydrogen atoms in each hydrogen environment

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10
Q

What does high resolution NMR tell us?

A
  • number of hydrogen environments
  • number of hydrogen atoms in each hydrogen environment
  • how many hydrogens are on adjacent carbon
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11
Q

What is the number of peaks on a NMR spectra equivalent to?

A

number of hydrogen environments

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12
Q

What is the height of a peak on a low resolution NMR spectra equivalent to?

A

how many hydrogen atoms are in that environment

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13
Q

What is the splitting pattern on a high resolution NMR spectra equivalent to?

A

the number of hydrogen atoms are on the adjacent carbon plus one
(N+1 rule)

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14
Q

What is the area under a cluster on a high resolution NMR spectra equivalent to?

A

number of hydrogen atoms in environment

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15
Q

How many hydrogens are on the adjacent carbon to a singlet?

A

0

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16
Q

How many hydrogens are on the adjacent carbon to a doublet?

A

1

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17
Q

How many hydrogens are on the adjacent carbon to a triplet?

A

2

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18
Q

How many hydrogens are on the adjacent carbon to a quartet?

A

3

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19
Q

How many hydrogens are on the adjacent carbon to a quintet?

A

4

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20
Q

What do you call the splitting pattern when there are 0 carbons on the adjacent carbon?

A

singlet

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21
Q

What do you call the splitting pattern when there is 1 carbon on the adjacent carbon?

A

doublet

22
Q

What do you call the splitting pattern when there are 2 carbons on the adjacent carbon?

A

triplet

23
Q

What do you call the splitting pattern when there are 3 carbons on the adjacent carbon?

A

quartet

24
Q

What is the N+1 rule?

A

the number of subpeaks within a cluster on a high resolution NMR is equivalent to the umber of hydrogen atoms on the adjacent carbon plus one

25
Q

What is the unit for chemical shift?

A

ppm

26
Q

What is chromatography?

A

a technique used to separate components of a mixture so that they can be identified
-uses a mobile and stationary phase

27
Q

What types of chromatography are there?

A
  • thin layer chromatography (TLC)
  • column chromatography
  • high performance liquid chromatography (HPLC)
  • gas chromatography (GC)
28
Q

What does TLC stand for?

A

thin layer chromatography

29
Q

What is the stationary phase in thin layer chromatography?

A

TLC plate coated in solid particles

30
Q

What is the mobile phase in thin layer chromatography?

A

solvent

31
Q

Rf =

A

distance moved by spot
_____________________
distance moved by solvent

32
Q

What does the height a component move up thin layer chromatography depend on?

A

its interactions with the stationary phase

-ie. if its moved higher up, it has greater interactions with plate

33
Q

What is the stationary phase in column chromatography?

A

solid (eg. silica) which is packed into column

34
Q

What is the mobile phase in column chromatography?

A

solvent (which runs down column with gravity)

35
Q

Name examples of a polar solvent that could be used with a non-polar silica in column chromatography

A

water
ethanol
ethanoic acid

36
Q

Name examples of a non-polar solvent that could be used with a polar silica in column chromatography

A

hexane
cyclohexane
hydrocarbons

37
Q

What does HPLC stand for

A

high performance/pressure liquid chromatography

38
Q

What is the stationary phase in high performance liquid chromatography?

A

solid packed into column

39
Q

What is the mobile phase in high performance liquid chromatography?

A

solvent

40
Q

What happens in high performance liquid chromatography (HPLC)?

A
  • solvent (and sample) are forced through horizontal column (packed with solid) under high pressure
  • detector at the end of column detects each compound and calculates its retention time (Rt)
41
Q

What does GC stand for?

A

gas chromatography

42
Q

What is the stationary phase in gas chromatography?

A

solid with high mp which is packed into column

43
Q

What is the mobile phase in gas chromatography?

A

inert gas (aka noble gas)

44
Q

What happens in gas chromatography (GC)?

A
  • an inert gas (eg. noble gas) acts as a solvent and is forced through column (packed with a solid) under high pressure by a pump
  • sample is injected into the column as a gas (sample may have been heated and vaporised first depending on its standard state) and is forced through column
  • detector detects each compound and calculates its retention time (Rt)
45
Q

Why is the column in an oven in gas chromatography?

A

to ensure sample is maintained as a vapour

46
Q

What must the gas used as a solvent in gas chromatography be?

A

inert/not reactive

ie. noble gas eg. helium

47
Q

What must the solid used as the stationary phase in gas chromatography be?

A

have a high mp

48
Q

What are the advantages of high performance liquid chromatography (HPLC) and gas chromatography (GC)?

A
  • faster
  • more accurate
  • can use smaller quantities
49
Q

What are the disadvantages of high performance liquid chromatography (HPLC) and gas chromatography (GC)?

A

-not so good at identifying components (∴ are used with mass spectrometry)

50
Q

Name two examples of when chromatography (HPLC/GC) is used with mass spectrometry

A
  • forensics

- drug testing

51
Q

Why are chromatography (HPLC/GC) and mass spectrometry used together?

A

mass spectrometry can be used to identify the substances HPLC/GC have separated (instead of using a detector)
as HPLC/GC are not so good at identifying

Alevel Chemistry Edexcel (19 decks)

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