spectrometry

Question 1

equation to calculate the energy of a photon

Answer 1

E=hv

Question 2

beer lambert law

Answer 2

A=ecl

Question 3

describe electromagnetic radiation diagram

Answer 3

electric field on y axis then magnetic field towards/away from me

Question 4

what is Hz

Answer 4

cycles per second/ s^-1

Question 5

equation with wavelength and frequency

Answer 5

wavelength is inversely proportional to frequency,
λ ∝1/ν

Question 6

wavelength symbol

Answer 6

λ

Question 7

frequency symbol

Answer 7

v

Question 8

speed of light equation

Answer 8

c = νλ
speed of light in a vacuum= 3x10^8 ms^-1

Question 9

describe the visible colour spectrum

Answer 9

purple————>red
higher frequency, shorter wavelength, higher energy

lower frequency, longer wavelength, lower energy

Question 10

how to calculate energy of a photon

Answer 10

E=hv
h is Planck’s constant
v is frequency

Question 11

what is h when calculating energy of a photon

Answer 11

Planck’s constant

Question 12

what is spectroscopy

Answer 12

study of interaction between electromagnetic radiation and matter

Question 13

explain spectroscopy in general terms

Answer 13

1. EMR with specific frequency is absorbed by molecule
2. molecule becomes excited
   (higher frequency=higher energy)

Question 14

explain UV/visible spectroscopy

Answer 14

1. EMR in uv/vis range of frequencies has energy corresponding to electronic transitions
2. when uv/vis radiation of specific frequency is absorbed, an electron is promoted to a higher energy level

Question 15

what is an orbital

Answer 15

region of space that can hold up to 2 electrons with opposite spin (know drawing)

Question 16

what are the shape of S and d orbitals

Answer 16

s- spherical
d- dumbbell (x y z)

Question 17

what is refraction

Answer 17

when light slows down

Question 18

photon energy diagram stuff

Answer 18

each transition has a different change in energy so absorbs a photon of different frequency, shorter wavelength=higher change in energy of photon

Question 19

what is the λmax

Answer 19

wavelength at which the sample has the highest absorbance

Question 20

describe a uv/vis spectrum graph

Answer 20

-absorbance on y axis and wavelength on x axis

-wavelength of uv light is varied

Question 21

difference between absorption and emission

Answer 21

absorption- energy absorbed from photon will increase energy

emission- photon given out so energy decreases

Question 22

why are broader absorptions observed when molecules are more complex

Answer 22

extra vibrational and rotational energy levels

Question 23

difference between atomic and molecule spectrums

Answer 23

atoms have sharp spectra and molecules have broader spectra due to vibrational and rotational energy levels

Question 24

why is the spectra of molecules broader than atoms

Answer 24

molecules have contribution of vibrational and rotational energy levels

Question 25

what is transmittance (T)

Answer 25

fraction of light intensity which passed through a sample unchanged

Question 26

how to calculate absorbance

Answer 26

absorbance= -log10(T)

Question 27

what is absorbance proportional to

Answer 27

concentration and path length of a sample

Question 28

what is e in beer lamberts law

Answer 28

molar absorptivity= absorbance of a 1 mol dm-3 sample with path length 1cm at a specific wavelength

Question 29

how to calculate transmittance through a sample

Answer 29

light after/light before

Question 30

what is beer lamberts law

Answer 30

A=ecl

Question 31

units of e

Answer 31

dm3mol-1cm-1

Question 32

how to find E on a beer lamberts graph

Answer 32

gradient/path length

Question 33

describe how infrared spectroscopy works

Answer 33

1. bonds/bond angles vibrate with a specific frequency 2. vibrational frequency depends on bond strength and atom mass 3. difference in energy between vibrational energy levels match the infrared part of the electromagnetic spectrum 4. when absorbing IR radiation, vibrations increase in amplitude (more vibrations=more energy)

Question 34

what is wave number and the symbol for it

Answer 34

number of waves per unit distance, ṽ

Question 35

what is wavenumber equivalent to

Answer 35

ṽ =1/λ wavenumber= 1/wavelength

Question 36

what happens to bond strength and size as frequency increases

Answer 36

bond strength increases and size decreases

Question 37

what is the wavenumber of OH

Answer 37

3200-3600

Question 38

what is the wavenumber of COOH

Answer 38

2500-3300

Question 39

what is the wavenumber of C-H

Answer 39

2850-3100

Question 40

what is the wavenumber of C=O

Answer 40

1630-1820

Question 41

what is Bo

Answer 41

magnetic field experienced by a nucleus

Question 42

what can cause a spin flip transition and where does the energy required come from

Answer 42

a photon of appropriate energy causes a spin flip, energy depends on the beff

Question 43

what is B elec

Answer 43

tiny magnetic field generated by electrons, B elec opposes the external magnetic field Bo

Question 44

describe the relationship between Bo and Belec and nucleus

Answer 44

Belec opposes Bo so the nucleus experiences a weaker magnetic field than Bo, electrons shield the nucleus from Bo, greater electron density, greater shielding effect

Question 45

what do electronegative elements do

Answer 45

attract electron density from adjacent groups

Question 46

what is beff

Answer 46

effective magnetic field, magnetic field felt by each atom, different for each atom therefore the change in energy is different and different energy photons absorbed, greater electron density lower beff

Question 47

how does electron density affect b eff

Answer 47

greater electron density=increased shielding=lower b eff because more b elec to oppose b o change in energy is lower and a lower energy photon is absorbed

Question 48

what is the ppm of aromatic protons

Answer 48

7-8

Question 49

what do the number of signals/peaks in H nmr represent

Answer 49

number of proton environments in a molecule

Question 50

what is integration number in H nmr

Answer 50

ratio of number of protons in each environment, area under signal, number of H in the environment

Question 51

what is multiplicity

Answer 51

signal shape (singlet,doublet,triplet), tells you number of protons in adjacent environments, N+1, if 2 protons in adjacent environment then it is a triplet

Question 51

what does mass spectrometry measure and how do is work

Answer 51

measures the mass to charge ratio of ions 1. ionise sample which may cause molecule to fragment 2. ions separated according to m/z 3. ions detected

Question 51

what are coupling constants

Answer 51

3J 4J, how many jumps it takes to reach next proton (?)

Question 51

things to look at when interpreting H nmr

Answer 51

chemical shift, integration, splitting

Question 51

how to do an elemental analysis

Answer 51

percentage of each element divided by mass, divide by smallest value, ratio

Question 51

what is the molecular ion peak

Answer 51

peak with the highest m/z

Question 52

isotope pattern difference between chlorine and bromine

Answer 52

1:1 pattern indicates presence of bromine, 3:1 indicates presence of chlorine

Question 52

how to determine the molecular weight of a compound from a mass spec

Answer 52

the peak with the highest m/z value is the mass of the compound (molecular ion peak)