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Chemistry Module 4 > Mass Spectrometry and Infrared Spectrometry > Flashcards

Mass Spectrometry and Infrared Spectrometry Flashcards

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1
Q

All molecules absorb….

A

infrared radiation

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2
Q

What does the amount of vibration of the bond depend on

A
  • bond strength
  • bond length
  • the mass of each atom involved in the bond
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3
Q

What do most bonds vibrate at

A

they vibrate at a frequency between 300-4000 which is the infrared part of the electromagnetic spectrum

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4
Q

What does absorbed infrared radiation do to the bonds

A

it makes the covalent bonds vibrate more with either a stretching or bending motion

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5
Q

What are the ways in which the bond vibrates

A

they either bend or stretch

- draw this

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6
Q

How can the absorbed energies of the bond be displayed

A

it is displayed on an infrared spectrum

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7
Q

What does the infrared spectrum help us determine

A

the infrared spectrum helps us determine details about a compounds chemical structure, it indicates the presence of functional groups in the compound under investigation

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8
Q

How does the infrared spectrometer work

A

A beam of infrared radiation is passed through a sample of the material under investigation, the beam contains a full range of frequencies in the infrared region
the molecules absorb some of the frequencies and the emerging beam is analysed to plot a graph of transmittance against frequency - this is the infrared spectrum of the molecule
- graph is plotted by a computer that analyses the radiation which passes through completely uninterrupted, and compare this with the radiation that has been passed through the material being investigated

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9
Q

How is the frequency of the infrared radiation measured

A

using wave numbers with the units of cm-1

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10
Q

Draw an infrared spectrum graph

A

DRAW IT

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11
Q

Describe the infrared spectrum graph

A
  • absorption is shown by peaks, this is where the radiation has been absorbed
  • these parts indicate the bonds present in the substance
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12
Q

Why do most organic compounds produce a peak at about 3000cm-1

A

due to absorption by C-H bonds - do not get this confused with O-H peak

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13
Q

How do you identify aldehydes and ketones

A
  • peak at 1680-1750cm-1 this represents a C=O bond in both aldehydes if this peak is present the substance contains a C=O bond
  • no O-H peak which makes it different from a carboxylic acid
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14
Q

How do you identify alcohols

A

peak at 3200-3500 represents an O-H group, if this peak is present then the substance analysed contains a O-H bond as part of the alcohol group

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15
Q

How do you identify carboxylic acids

A
  • has to have a broad peak at 2500-3300 cm-1 which indicates the presence of the O-H group is a carboxylic acid
  • strong sharp peak at 1680-1750 cm-1, this represents the C=O group in a carboxylic acid
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16
Q

What is a molecular ion

A

this is the positive ion formed in mass spectrometry when a molecule loses an electron

17
Q

What happens when an organic compound is driven through a mass spectrometer

A
  • it is vapourised and driven through the mass spectrometer - some molecules lose an electron each and are ionised, the resulting ion is called the molecular ion
  • sample then undergoes fragmentation
  • acceleration of ions
  • deflection of ions
18
Q

Describe concepts about molecular ions

A
  • the mass of the lost electron is negligible
  • the molecular mass ion has a molecular mass equal to the relative molecular mass of the compound
  • molecular ions can be detected an analysed
19
Q

Describe the breaking of molecular bonds by fragmentation

A

excess energy from the ionisation process can be transferred to the molecular ion making it vibrate

  • this causes the bonds to weaken and the molecular ion can split into pieces by fragmentation
  • this means that the original molecules break up into positive fragment ions and other neutral species
20
Q

WRITE A FRAGMENTATION REACTION

A

PG 220

21
Q

What is detected in a mass spectrometer

A
  • molecular ions

- fragment ions

22
Q

What produces the peak with the highest mass change (M/Z) value in the mass spectrum

A

the molecular ion

- other peaks are as a result of fragmentation

23
Q

What does high resolution mass spectrometry do

A
  • it produces a spectrum with extreme precise values for the molecular ion, making accurate molecular mass determination easy
24
Q

What is mass spectrometry used for

A
  • it is used to determine the structure of an unknown compound and give it its precise identity
25
Q

What do fragmentation patterns do

A
  • although the molecular ion peak of two isomers will have the same M/Z value the fragmentation patterns will be different
  • each organic compound produces a unique mass spectrum which can be used as a fingerprint for identification
  • mass spectra of isomers will have the same molecular ion peak but they will have different fragmentation patterns for each one
26
Q

How do you identify the organic structure using fragmentation patterns

A
  • can be used to work out some of the molecules structural detail
27
Q

DRAW AN MOLECULAR ION FRAGMENTED EQUATION

A

PG 222

28
Q

What is elemental analysis

A
  • gives scientists information about the numbers and types of elements present in a compound sample
29
Q

What is mass spectra

A

mass spectra is a destructive analytical technique because the sample can not be reclaimed after analysis

30
Q

What are the advantages for mass spectra

A
  • small quantities

- cheap method of analysis

31
Q

What is elemental analysis used for

A
  • works out empirical formula
  • relative molecular mass
  • molecular formula
32
Q

What is infrared spectroscopy used for

A
  • monitor gases causing air pollution
  • modern breathalysers to measure ethanol in the breath
  • detect toxic leaks from industrial plants
33
Q

What is the basis behind using infrared spectroscopy in breathalysers

A

O-H bond absorbs some of the infrared radiation and vibrates this creates a peak in the infrared spectroscopy and indicates that there is an alcohol present, the level of absorption Is related to the concentration of alcohol in the blood this is the beer-lambert law

34
Q

What is used alongside infrared spectroscopy in modern breathalysers

A

sometimes other substances in breath produce a similar spectra so they combined IS with other technology such as chemical reactions to allow more specific results to be obtained on the concentration present
- provides evidence for law courts

35
Q

why is infrared spectroscopy used in air pollution

A
  • can be measured and monitored the amount of air pollution
36
Q

What is the link between infrared spectroscopy and green house gases

A

C=O, O-H, C-H, are good at absorbing infrared radiation present in greenhouse gases, as we release more gases more infrared radiation is absorbed this leads to global warming, more infrared radiation is absorbed therefore the earth gets hotter than if less infrared radiation is absorbed
- it is in CFCs?,

Chemistry Module 4 (8 decks)

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