Chapter 17 Spectroscopy

Question 1

what is mass spectrometry

Answer 1

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

Question 2

describe the first stage of mass spectrometry

Answer 2

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

Question 3

describe the second stage of mass spectrometry

Answer 3

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

Question 4

describe the third stage of mass spectrometry

Answer 4

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

Question 5

describe the fourth stage of mass spectrometry

Answer 5

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

Question 6

what does M+ represent

Answer 6

the moecular ion peak

Question 7

what is the molecular ion peak

Answer 7

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

Question 8

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

Answer 8

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

Question 9

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

Answer 9

fragment ions

Question 10

what causes fragmentation

Answer 10

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

Question 11

why are fragment ions useful

Answer 11

they allow us to determine the structure of a molecule

Question 12

what energy can bonds absorb

Answer 12

infrared energy

Question 13

what can absorbing infrared energy do to a bond

Answer 13

make it vibrate more

Question 14

what are the two types of bond vibration

Answer 14

bond stretching

bond bending

Question 15

what two factors affect how much a bond stretches or bends

Answer 15

mass of atoms in the bond

strength of bond

Question 16

what are the ideal factors for maximum bond vibration

Answer 16

heavy atoms

strong bonds

Question 17

how does the frequency of infrared vary between bonds

Answer 17

different bonds absorb different frequencies of infrared energy

Question 18

what does the infrared spectra show

Answer 18

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

Question 19

why are wavenumbers used instead of frequencies

Answer 19

frequencies are extremely large values so using wavenumbers is more convenient

Question 20

what do the peaks in an infrared spectra mean

Answer 20

infrared energy of that wavenumber has been absorbed by the sample

Question 21

why is infrared spectroscopy useful

Answer 21

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

Question 22

what is the fingerprint region

Answer 22

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

Question 23

why is the fingerprint region useful

Answer 23

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

Question 24

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

Answer 24

> 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

Question 25

give two uses of IR spectroscopy

Answer 25

breathalyser

pollutant sensor

Question 26

how does IR spectra work in breathalysers

Answer 26

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

Question 27

how does the IR spectra work in pollutant sensors

Answer 27

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

Question 28

what is the first stage of the greenhouse gas effect

Answer 28

UV and visible energy waves emitted by the sun and these high energy waves reach earth

Question 29

what is the second stage of the greenhouse gas effect

Answer 29

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

Question 30

what is the third stage of the greenhouse gas effect

Answer 30

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

Question 31

what is the fourth stage of the greenhouse gas effect

Answer 31

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

Question 32

give 5 sources of greenhouse gases

Answer 32

general pollution
combustion of fossil fuels
agriculture
deforestation
landfills