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2016 GAMSAT > Chemistry - Rings, Polymers and Analysis - F324 - Separation by Chromatography (3) > Flashcards

Chemistry - Rings, Polymers and Analysis - F324 - Separation by Chromatography (3) Flashcards

1
Q

What is the advantage of chromatography?

A

Chromatography can separate out components with similar physical properties in very complex mixtures.

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2
Q

Define a phase in chromatography?

A

A phase is a physically distinctive form of a substance, such as the solid, liquid and gaseous states of ordinary matter.

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3
Q

Define the mobile phase.

A

The mobile phase is the phase that moves in chromatography.

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4
Q

Define the stationary phase.

A

The stationary phase is the phase that does not move in chromatography.

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5
Q

On which basis does chromatography work?

A

Chromatography works on the basis that different components have different affinities for a stationary phase and for a mobile phase.

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6
Q

What is the stationary phase in thin layer chromatography?

A

In thin layer chromatography, the stationary phase is a solid.

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7
Q

What is the mobile phase in thin layer chromatography?

A

In thin layer chromatography, the mobile phase is a liquid.

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8
Q

What is the stationary phase in gas chromatography?

A

In gas chromatography, the stationary phase is a solid or a liquid mounted on a solid support.

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9
Q

What is the mobile phase in gas chromatography?

A

The mobile phase in gas chromatography is a gas.

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10
Q

What does a solid stationary phase separate via?

A

A solid stationary phase separates via adsorption.

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11
Q

What does a liquid stationary phase separate via?

A

A liquid stationary phase separates via relative solubility.

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12
Q

Define adsorption.

A

Adsorption is the process by which a solid holds more molecules of a gas or liquid or solute as a thin film on the surface of a solid or, more rarely, a liquid.

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13
Q

What is usually used as the stationary phase of thin layer chromatography?

A

The stationary phase of TLC is usually a thin layer of an adorbent such as silica gel (SiO2) or alumina (AlO3) coated on a flat, inert support, usually a sheet of glass.

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14
Q

How is the Rf value calculated?

A

Rf = distance moved by component / distance moved by the solvent front

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15
Q

What are some of the negatives of chromatography?

A
  • similar compounds will have similar Rf values
  • unknown compounds have no reference Rf value
  • it may be difficult to find a solvent that separates all the components in a mixture
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16
Q

What needs to be considered when choosing a suitable solvent for chromatography?

A
  • if the components are very soluble then they will be washed all the way up the plate
  • if the components are not very soluble then there will be very little movement
  • trial and error may be necessary to find a suitable solvent.
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17
Q

What type of compounds is gas chromatography most useful for separating?

A

Gas chromatography is particularly useful for organic compounds that have a low boiling point and evaporate easily

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18
Q

What is the stationary phase in gas chromatography?

A

The liquid for the stationary phase id often a long chain alkane with a high boiling point. e.g silicone polymers.

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19
Q

What is the tubing in gas chromatography referred to as?

A

The tubing in gas chromatography is referred to as the chromatography column.

20
Q

What is the mobile phase in gas chromatography?

A

The mobile phase is an inert or unreactive carrier gas such as helium or nitrogen.

21
Q

How can the separation in gas chromatography be improved?

A

The separation can be improved by using different oven temperatures and different flow rates for the carrier gas.

22
Q

What are some of the negatives of gas chromatography?

A
  • potentially thousands of chemicals have the same retention time, peak shape and detector response
  • not all parts of the mixture will necessarily be separated or detected.
  • unknown compounds have no reference retention time.
23
Q

What are the isotopes most commonly used in NMR spectroscopy?

A

1H, 13C, 19F and 31P

24
Q

What creates the magnetic field for NMR spectroscopy?

A

Unpaired nucleons and their residual spin creates the magnetic field.

25
Q

What is resonance?

A

The excitation and relaxation of the nucleus is called resonance.

26
Q

What is used as the reference peak in NMR?

A

Tetramethylsilane (TMS) (CH3)4Si is used as the reference peak.

27
Q

Why is TMS used as the reference?

A

TMS is used as the reference because it is chemically unreactive and volatile so it can easily be removed from the sample after running an NMR spectrum.

28
Q

Why are NMR spectra run with deuterated solvents?

A

Because you cannot use a regular organic solvent because the carbon and hydrogen within them also produce a signal. Deuterium has an even number of nucleons so produces no signal.

29
Q

What does the number of peaks in carbon-13 NMR tell you?

A

The number of peaks in carbon-13 NMR tells you the number of different carbon environments.

30
Q

What do the chemical shifts in carbon-13 NMR spectra tell you?

A

The chemical shifts in carbon-13 NMR tell you the types of carbon environment.

31
Q

What does the size of the peaks in carbon-13 NMR tell you?

A

The size of the peaks in carbon-13 NMR tells us nothing.

32
Q

Why does proton NMR require far less material than carbon NMR?

A

1H is the commonest isotope of hydrogen with a relative abundance of 99.9% compared with 13C which has a relative abundance of 1.1%.

33
Q

What does the number of peaks in proton NMR tell us?

A

The number of peaks in proton NMR tells us the number of proton environments.

34
Q

What does the chemical shift in proton NMR tell us?

A

The chemical shift in proton NMR gives the type of proton environment of each peak.

35
Q

What do the relative peak areas in proton NMR tell us?

A

The relative peak areas in proton NMR give the proportions of protons in each environment.

36
Q

What does spin-spin coupling tell us?

A

Spin-spin coupling gives us information about adjacent protons.

37
Q

What is the rule for predicting the splitting pattern due to spin-spin coupling?

A

We predict the splitting pattern using the n+1 rule.

38
Q

Why can it be difficult to identify the protons of OH and NH peaks?

A

It can be difficult to identify the OH and NH peaks as they can appear over a wide range of different chemical shift values depending on the solvent and concentration of the sample.

39
Q

What is the common name for deuterium oxide?

A

The common name for deuterium oxide is heavy water.

40
Q

How can OH and NH peaks be specifically identified?

A

A proton NMR is run, D2O is then added and shaken, then a second NMR is run which makes any peaks due to OH or NH disappear.

41
Q

How does an OH or NH peak usually show on a spectrum?

A

An OH or NH peak usually shows as a singlet which may be broad.

42
Q

What are the advantages of MRI scanners?

A

MRI scanners are harmless and non-invasive.

43
Q

Patients with what should not have MRI scans?

A

Patients with ferromagnetic implants should not undergo MRI scanning.

44
Q

What key information does mass spectrometry tell us?

A

Mass spectrometry tells us the percentage by mass of each element.

45
Q

What key information does infrared spectroscopy tell us?

A

Infrared spectroscopy gives information about bonds and functional groups that are likely to be present.

46
Q

What key information does C13 NMR tell us?

A

C13 NMR gives information about the number and types of carbon environments in each molecule.

47
Q

What key information does proton NMR tell us?

A

Proton NMR gives information about numbers and types of proton environment and the number of protons on adjacent carbon atoms.

2016 GAMSAT (19 decks)

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