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Edexcel Chemistry Unit 4 > 4.9 Spectroscopy & Chromatography > Flashcards

4.9 Spectroscopy & Chromatography Flashcards

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1
Q

Give the ranges of wavelengths for UV light.

A

Between visible light and X-rays, 400nm to 10nm.

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2
Q

How does UV light initiate reactions?

A

UV radiation has enough energy to split molecules, producing free radicals.

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3
Q

Give an example of an equation of a reaction where UV radiation splits a molecule into radicals. Describe the movement of electrons during the reaction.

A

Cl-Cl -UV→ Cl• + Cl• Each chlorine takes one atom from the convent bond.

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4
Q

What is homiletic fission?

A

When the electron pair from a bond goes to two different atoms.

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5
Q

Name of source of energy that initiates a reaction between chlorine and methane.

A

UV radiation from the sun.

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6
Q

What happens in an invitation step of a free radical reaction?

A

Free radicals are formed.

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7
Q

What happens in a propagation step?

A

A radical reacts with a molecule, producing another radical that can go on and react.

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8
Q

Give an example of two propagation steps where a Cl• is ultimately regenerated.

A

CH4 + Cl• → CH3• + HCl

CH3• + Cl2 → CH3Cl + Cl•

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9
Q

Give two examples of termination steps of a free radical mechanism.

A

Cl• + CH3• → CH3Cl

CH3• + CH3• → C2H6

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10
Q

Give the equation to show how chlorine radicals form from CFCs.

A

CF3Cl -UV→ CF3 + Cl•

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11
Q

Give the two propagation steps that show how one Cl• can destroy thousands of ozone molecules.

A

Cl• + O3 → O2 + ClO•

ClO• + O3 → Cl• + 2O2

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12
Q

Explain why CFCs are so damaging to the ozone layer.

A

A chlorine radical from one CFC can convert thousands of ozone molecules to oxygen molecules.

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13
Q

State the range of wavelengths that microwaves fall between.

A

1mm and 1m.

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14
Q

Give two uses for microwave radiation.

A

Communication and heating.

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15
Q

Give the wavelength of microwaves used in a microwave oven.

A

12.24cm.

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16
Q

In a covalent bond, where are the electrons pulled towards?

A

The more electronegative atom.

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17
Q

What is a polar bond?

A

A bond where electrons are pulled toward one atom.

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18
Q

Give three examples of polar chemicals.

A

Water, fats and sugars.

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19
Q

How do microwave ovens work?

A

Microwaves are passed through food, creating an electric field. Polar molecules try to line up with the field by rotating, causing them to collide with other molecules, generating heat.

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20
Q

Give three uses of microwaves other than heating food.

A

Killing cancer cells with narrow beams. For efficiently heating reactants in the chemical industry. Drying wood, paper and textiles.

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21
Q

What can a mass spectrometer show?

A

Relative amounts of ions with different mass-to-charge ratios.

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22
Q

Where is the M peak on a mass spectrum?

A

The second highest.

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23
Q

What causes the highest peak on a mass spectrum?

A

Carbon 13.

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24
Q

What does the M peak show?

A

Its m/e value is the molecular mass of the molecule being studied.

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25
Q

What is relative abundance?

A

The abundance of an ion in a mass spectrum compared to the most abundant ion in the same spectrum.

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26
Q

What does the m/e value represent?

A

The mass of an ion divided by it’s charge, which is usually +1.

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27
Q

What can the molecular ions be broken down into in a mass spectrometer?

A

A fragment ion and a free radical.

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28
Q

What would the m/e value of a CH3CH2+ ion be?

A

29.

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29
Q

Why don’t free radicals show up on mass spectra?

A

They are “lost”.

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30
Q

What is the use of fragmentation patterns?

A

They can show the structure of a molecule.

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31
Q

What cases a nucleus to have spin?

A

An odd number of nucleons.

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32
Q

What does spin cause an atom to have?

A

A weak magnetic field.

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33
Q

What does NMR observe?

A

How the tiny magnetic fields of atoms react when they are placed in a much larger external magnetic field.

34
Q

Which element does protons NMR observe?

A

Hydrogen.

35
Q

What can proton NMR find out?

A

How many hydrogens there are in an organic molecules and how they’re arranged.

36
Q

What happens to the magnetic field of protons of a molecule that are not place in an external magnetic field?

A

They spin in random directions, cancelling out their magnetic fields.

37
Q

In NMR, what happens when a strong external magnetic field is applied?

A

Protons align themselves either with the field or opposing it.

38
Q

Which protons are at a higher energy level, aligned protons or opposing protons?

A

Opposing protons.

39
Q

How do protons aligned with the external field move to the higher energy level, opposing the magnetic field.

A

Absorbing right waves of a certain frequency.

40
Q

How do protons opposing the external field move to the lower energy level, aligned with the magnetic field.

A

Emitting radio waves.

41
Q

What does NMR measure and why?

A

Overall absorption of radio wave energy since there are more aligned protons.

42
Q

Protons in different environments absorb…

A

different amounts of energy.

43
Q

What affects the environment of a proton?

A

Shielding by surrounding electrons or other groups of atoms near a nucleus.

44
Q

What does a proton’s environment affect?

A

The amount of energy aboard by a proton and the frequency they absorb at.

45
Q

What is the requirement for two protons to be in the same environment?

A

They must be joined to exactly the same thing.

46
Q

How many different hydrogen environments does 2-chloropropane have?

A

2

47
Q

How many different hydrogen environments does 1-chrlorobutane have?

A

4

48
Q

What are the differences in absorption measured relative to?

A

TMS, tetramethylsilane.

49
Q

What is chemical shift measured in?

A

Parts per million, ppm.

50
Q

What do the number of peaks on an NMR spectra represent?

A

The number of different hydrogen environments.

51
Q

What do relative areas under NMR peaks represent?

A

How many protons are in that environment.

52
Q

What can you use to identify the proton causing chemical shift?

A

The table given in the data booklet.

53
Q

What effect does spin-spin coupling have on NMR peaks?

A

It splits the peaks.

54
Q

Which protons cause spin-spin coupling and therefore peak splitting?

A

Protons that are on adjacent carbon atoms.

55
Q

What is the n+1 rule?

A

If there are n neighbouring single protons, the peak will be split into n+1.

56
Q

What does MRI stand for?

A

Magnetic Resonance Imagery.

57
Q

How does MRI work?

A

Humans are place in a large magnet and irradiated with radio waves. The hydrogen nuclei in water molecules in their bodies absorb different frequencies deepening on what tissue they are in. A series of images are taken to produce a 3D model.

58
Q

What is the advantage of using MRI rather than X-rays machines?

A

X-rays can cause cancer.

59
Q

Explain one use of NMR.

A

It is used in the pharma industry to monitor the purity of products by camping readings to a know “fingerprint” of a molecule.

60
Q

What is the purpose of infrared spectroscopy?

A

It helps you identify organic molecules.

61
Q

How does infrared spectroscopy work?

A

A bean of IR radiation goes through a sample. The IR energy is absorbed by the bonds in the molecules, increasing their vibrational energies. Different bonds in different places absorb different wavelengths, so bonds can be identified from absorption spectra.

62
Q

What does a peak on a transmittance vs wavenumber graph represent.

A

A wavelength of light that is being absorbed by bonds in the sample.

63
Q

How can IR spectroscopy be used while a reaction is in process?

A

It can show the progress of the reaction as peaks from functional groups in reactants disappear whilst peaks from products appear.

64
Q

What are the commercial uses of IR spectroscopy?

A

Measuring the progress of a reaction in the chemical industry. Measuring the degree of polymerisation in polymer manufacture, the number of double bonds changes. Spotting invisible cracks in polymers where why have been oxidised.

65
Q

What is chromatography used for?

A

Separating and identify chemicals.

66
Q

Give two types of chromatography.

A

Gas chromatography and high-pressure liquid chromatography.

67
Q

Briefly outline the two phases of chromatography.

A

The mobile phase, where molecules can move (always gas or liquid). The stationary phase, where molecules can’t move (a solid or liquid held in a solid).

68
Q

What is the stationary phase in gas chromatography?

A

A vicious liquid, such as oil, that coats the inside of a long tube in an oven.

69
Q

What is the mobile phase in gas chromatography?

A

An uncreative carrier gas such as nitrogen.

70
Q

How does gas chromatography work?

A

The sample gets injected into carrier stream as a gas. The amount that each component of the sample absorbs to the stationary phase is different, meaning they have different retention times.

71
Q

What is retention time of a sample?

A

The time taken between being injected and recorded at the other end.

72
Q

What does a gas chromatography detector measure?

A

Thermal conductivity of the gasses leaving the tube.

73
Q

What graph does a gas chromatography recorder produce?

A

Detector response vs time. Area under the peak show amount of each component and time show retention time.

74
Q

What is the stationary phase in HPLC?

A

Small particles of a solid packed into a tube. Often silica bonded to other hydrocarbons.

75
Q

What is the mobile phase in HPLC?

A

A polar mixture such as methanol and water, forced through the tube under high pressure.

76
Q

How does high-performance liquid chromatography work?

A

The sample is injected into the stream solvent and is carried though the tube as a solution (the tube isn’t heated). A mass spectrometer analyses each component as it is collected.

77
Q

How is the mixture separated in HPLC?

A

Different parts of the mixture are attracted by different amounts to the solid, so they take different times to travel through the tube.

78
Q

How is retention time measured?

A

Measuring absorption of UV light.

79
Q

Give examples of circumstances where HPLC can be whilst and GC can’t.

A

When the sample is heat sensitive or has a high boiling point.

80
Q

Explain the industrial use of gas chromatography.

A

It is used to check the purity of products in a continuous process. A small amount of product is diverted to GC apparatus at regular time intervals. If impurities are too high the process can be automatically shut down.

81
Q

Explain the industrial use of high-performance liquid chromatography.

A

It can be used to check that industrial equipment is clean because it is a very sensitive method of analysis.

Edexcel Chemistry Unit 4 (6 decks)

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