Chapter 17 Spectroscopy Flashcards

(32 cards)

1
Q

what is mass spectrometry

A

a scientific method used to determine the relative atomic mass of an element or the relative molecular mass of a molecule

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2
Q

describe the first stage of mass spectrometry

A

the sample is vaporised so that it is in a gaseous state before entering the vacuum

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3
Q

describe the second stage of mass spectrometry

A

the gaseous sample enters the ionisation chamber where an electron is removed to make the molecule/atom a positive ion

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4
Q

describe the third stage of mass spectrometry

A

the ions enter the acceleration chamber where their velocities are increased to the same KE

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5
Q

describe the fourth stage of mass spectrometry

A

the accelerated ions enter the drift region where they separate out due to their varying masses and strike a detector that is tuned to only detect 1+ ions as a mass to charge ration or m/z ration

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6
Q

what does M+ represent

A

the moecular ion peak

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7
Q

what is the molecular ion peak

A

the peak furthest to the right of the mass spectra that has a m/z value equal to the Mr/Ar of the whole molecule/atom

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8
Q

why is there sometimes a very small peak one unit to the right of the M+ peak called M+1

A

1.1% of carbon atoms are carbon-13 increasing the mass of the molecule by 1.

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9
Q

what is the name given to all peaks before the molecular ion peak

A

fragment ions

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10
Q

what causes fragmentation

A

when the molecule is vaporised and then ionised it sometimes breaks apart to form two smaller molecules one takes both electrons and one loses both electrons creating a radical and fragment ion

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11
Q

why are fragment ions useful

A

they allow us to determine the structure of a molecule

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12
Q

what energy can bonds absorb

A

infrared energy

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13
Q

what can absorbing infrared energy do to a bond

A

make it vibrate more

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14
Q

what are the two types of bond vibration

A

bond stretching

bond bending

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15
Q

what two factors affect how much a bond stretches or bends

A

mass of atoms in the bond

strength of bond

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16
Q

what are the ideal factors for maximum bond vibration

A

heavy atoms

strong bonds

17
Q

how does the frequency of infrared vary between bonds

A

different bonds absorb different frequencies of infrared energy

18
Q

what does the infrared spectra show

A

how much infrared of a certain frequency is transmitted through a sample

19
Q

why are wavenumbers used instead of frequencies

A

frequencies are extremely large values so using wavenumbers is more convenient

20
Q

what do the peaks in an infrared spectra mean

A

infrared energy of that wavenumber has been absorbed by the sample

21
Q

why is infrared spectroscopy useful

A

the wavenumbers absorbed correspond to a certain bond so we can determine the different bonds and functional groups present in a molecule

22
Q

what is the fingerprint region

A

part of IR spectra below 1500cm^-1 that has multiple peaks so is very complex

23
Q

why is the fingerprint region useful

A

because it is so complex every single molecule has its own unique fingerprint region which can be used to identify it

24
Q

describe the three Ir spectra you need to know and the homologous series they relate to (values not important)

A

> alcohol - has a broad peak left side for O-H bond
aldehyde/ketone - has a thin peak in the middle for C=O
carboxylic acid - has both thin peak in middle for C=O and broad peak left side for O-H

25
give two uses of IR spectroscopy
breathalyser | pollutant sensor
26
how does IR spectra work in breathalysers
they can detect the C-O bond which you shouldn't be exhaling unless you have an organic compound like alcohol in your system or a rare medical condition. This is indicated by a colour change
27
how does the IR spectra work in pollutant sensors
they can detect the C=O bonds in carbon dioxide, C-H bonds in methane and O-H bonds in water allowing us to monitor the level of greenhouse gas emissions in an area
28
what is the first stage of the greenhouse gas effect
UV and visible energy waves emitted by the sun and these high energy waves reach earth
29
what is the second stage of the greenhouse gas effect
some of the high energy waves absorbed by the ozone layer the rest is re-emitted from the earth into space in all directions as lower energy infrared waves
30
what is the third stage of the greenhouse gas effect
the IR is absorbed by molecules in the atmosphere increasing bond vibrations and putting the molecules into a higher energy state where they are unstable
31
what is the fourth stage of the greenhouse gas effect
the unstable molecules want to get rid of their extra and return to a relaxed stable state so emit infrared energy back to earth heating the planet up
32
give 5 sources of greenhouse gases
``` general pollution combustion of fossil fuels agriculture deforestation landfills ```