spectroscopy

Question 1

what is spectroscopy ?

Answer 1

the use of radiation to observe changes in moclules

Question 2

what is within the methods of spectroscopy ?

Answer 2

• use a tiny amount of sample
• are non destructive

Question 3

how will the infrared radiation be absorbed by ?

Answer 3

by the bonds in molecules causing vibrations

Question 4

what are the two common vibrations ?

Answer 4

stetches and bends

Question 5

a molecule will only absorb a significant amount of infrared radiation if what ?

Answer 5

there is a change in the dipole moment (polarity) following a vibration

Question 6

what do greenhouse gases do ?

Answer 6

absorb infrared and reemit it toward the Earth ( trapping heat )

Question 7

what is the power as a greenhouse gas - nitrogen / oxygen ? Reason ?

Answer 7

no effect at all - no polarity so symmetrical and no polar bond

Question 8

what is the power as a greenhouse gas - water vapour ? Reason ?

Answer 8

very strong but short lived - polar so asymmetrical and polar bond but will condense and rain

Question 9

what is the power as a greenhouse gas - methane ? Reason ?

Answer 9

moderate - not polar so weakly polar bonds, symmetrical and has more bonds and can stretch and bend asymmetrically

Question 10

what is the power as a greenhouse gas - nitrogen oxides ? Reason ?

Answer 10

strong - polar bonds and asymmetrical

Question 11

what is the power as a greenhouse gases - carbon dioxide? Reason ?

Answer 11

weak - non polar can stretch asymmetrically so bending is unlikely due to pi bonding

Question 12

what is the power as a greenhouse gas - CFCs and SF6? Reason ?

Answer 12

very strong - strong polar bonds and asymmetrical

Question 13

what two pieces of information does an IR spectrometer hep determine the identity of a molecule ?

Answer 13

transmittance of IR
wavenumber - energy

Question 14

what is the transmittance ?

Answer 14

the amount of infrared radiation that passes through the analyte

Question 15

the lower the transmittance the more of what is present

Answer 15

bond

Question 16

what does the wavenumber describe ?

Answer 16

the energy of the infrared radiation

Question 17

the higher the wavenumber, …

Answer 17

the higher the energy

Question 18

what is a change in dipole moment ?

Answer 18

following the vibration the delta positive / negative of the molecule will change

Question 19

when will there be a change in dipole moment ?

Answer 19

the molecule needs to polar so has to have a polar bond and lack symmetry

Question 20

what are the five stages of mass spectrometry called ?

Answer 20

stage 1: vaporisation
stage 2: ionisation
stage 3 : acceleration
stage 4 : deflection
stage 5: detection

Question 21

Stage 1: vaporisation

Answer 21

in order to pass through the spectrometer the sample must be vaporised using heat or electrical energy

Question 22

Stage 2 : ionisation

Answer 22

a beam of high energy electrons are fired at the analyte molecules - knock electrons from the molecule

Question 23

ionisation:
M -> M+ (e-)
what is this called ?

Answer 23

molecular or parent ion

Question 24

what is fragmentation ?

Answer 24

the energy from the electron can also cause fragmentation of the molecular ion

Question 25

Stage 3 : acceleration

Answer 25

an electric field is then used to accelerate any ions formed ionisation and fragmentation

Question 26

stage 4 : deflection

Answer 26

a magnetic field is used to deflect ions toward detector

Question 27

what does the mass and charge of the ion determine ?

Answer 27

if it reaches the detector

Question 28

Stage 5 : detection

Answer 28

the ions hit a metal copper plate which emits electrons - creates a current which detects the ion

the relative intensity number of that mass/ charge ion is then recorded

Question 29

what is mass/ charge called ?

Answer 29

m/z of a ion

Question 30

how is mass spectrometry identify its molecules by their mass to charge ratio achieved by ?

Answer 30

-ionising the unknown molecule
-accelerating the ions using an electric field
-deflecting the ions using a magnetic field
-detecting the ions to calculate their mass/ charge

Question 31

ionisation

Answer 31

m + e- -> [M]+. + 2e-
unknown molecule + high energy electron -> parent ion

C3H8 + e- -> [C3H8]+. + 2e-

Question 32

what does the size of a peak show ?

Answer 32

how stable the ion is

Question 33

the more stable ions typically be secondary / tertiary carbocations

Answer 33

these make larger peaks on mass spectra

Question 34

when fragmenting your molecule how many bonds would you break ?

Answer 34

only one bond - starts with single bond