L5 Rich: uv-visible spectroscopy

Question 1

when reds absorbed what’s wavelength and transmitted colour?

Answer 1

700-620

green

Question 2

when orange absorbed what’s wavelength and transmitted colour?

Answer 2

620-580

blue

Question 3

when yellow absorbed what’s wavelength and transmitted colour?

Answer 3

580-560

violet

Question 4

when greens absorbed what’s wavelength and transmitted colour?

Answer 4

560-490

red

Question 5

when blue absorbed what’s wavelength and transmitted colour?

Answer 5

490-430

orange

Question 6

when violet absorbed what’s wavelength and transmitted colour?

Answer 6

430-380

yellow

Question 7

what part can the human see?

Answer 7

the UV Vis region

Question 8

does UV vis tell us about the structure of a molecule?

Answer 8

no

Question 9

what does Uv vis tell us about?

Answer 9

quantity, absorption maximum.

Question 10

what does a commercial spectrophotometer over?

Answer 10

185 –900 nm range

Question 11

with a commercial spectrophotometer where can you get interference?

Answer 11

190, as water and oxygen in the air will cause peaks

Question 12

what is the origin absorption of Electronic Spectroscopy of Molecules?

Answer 12

Interaction of photons with ions or molecules

Question 13

what happens when a molecule absorbs a photon ?

Answer 13

when a molecule absorbs a photon form the Uv visible region, the energy is captured by the outer most electrons and leads to a change in electronic energy

Question 14

Does UV vis cause a change in vibrational energy?

Answer 14

no that happens in Raman spectroscopy

Question 15

what does the change in electronic energy levels cause?

Answer 15

Results in alteration of vibrational and rotational energy

Question 16

how many wave numbers do we need for UV vis spectroscopy ?

Answer 16

10,000 wave numbers in energy

Question 17

when carrying out Uv vis spectroscopy what peaks do we see?

Answer 17

mainly broad peaks

covers multiple peaks occurring ta the same time

Question 18

absorption of photons takes how long?

Answer 18

10-18 s

Question 19

in uv vis what stem axis of the graph

Answer 19

wavelength, transmittance/absorbance/reflectance

Question 20

what stem units of wavelength?

Answer 20

nm

Question 21

what is transmittance?

Answer 21

measure of intensities of transmitted and incident light

Question 22

in ramane and infrared the x axis is in?

Answer 22

wavenumber

Question 23

what’s transmittance equation?

Answer 23

I/i0

Question 24

what happens when UV vis is does on gases?

Answer 24

spectra shows fine structure, vibrational transitions - big peaks
rotational transitions - within big peaks

Question 25

For Uv vis whats the sample prep?

Answer 25

- dissolve sample into solution

Question 26

what can uV vis be done on?

Answer 26

gas liquid and solid

Question 27

water has a maximum absorption wavelength of?

Answer 27

190nm ( in UV)

Question 28

polar solid will need a ?

Answer 28

polar solvent

Question 29

when preparing for Uv vis you need to know?

Answer 29

the concentration

Question 30

cuvettes come in?

Answer 30

Quartz or glass or plastic

Question 31

is glass cuvettes used during UV?

Answer 31

no use quartz

Question 32

when using organic solvents, don't use?

Answer 32

plastic cuvette

Question 33

what's the beer lambert law equation?

Answer 33

A=ecl

Question 34

what is A?

Answer 34

absorbance

Question 35

what's E?

Answer 35

molar absorption coefficient | dm3 mol-1 cm-1

Question 36

what's c?

Answer 36

concentration in mol dm-3

Question 37

what's l?

Answer 37

path length in cm (usually 1 )

Question 38

what do you plot?

Answer 38

C against A (straight diagonal line)

Question 39

whats the other equation?

Answer 39

A= - log 10T T=10^-A

Question 40

Uv vis spectroscopy mainly uses ?

Answer 40

organic compounds

Question 41

How many transmissions do we need to know?

Answer 41

2 transmissions

Question 42

what are the 2 transmissions?

Answer 42

n →π* and π→π*

Question 43

n →π*

Answer 43

n electron to lowest π* anti bonding orbital

Question 44

when does n →π* happen?

Answer 44

heteroatom with lone pair of electrons

Question 45

π→π*

Answer 45

highest π orbital to lowest π* anti bonding orbital.

Question 46

which has a more intense peak?

Answer 46

π→π*

Question 47

which has a small peak?

Answer 47

n →π*

Question 48

in transition metal compounds what transition happens?

Answer 48

d → d

Question 49

for d → d what do you need?

Answer 49

partially filled d orbitals

Question 50

what colour is chlorophyll?

Answer 50

green

Question 51

what are chromophore groups functional for?

Answer 51

Functional groups responsible for absorption

Question 52

what happens to the band of a chromophore group ?

Answer 52

Position and intensity of absorption band constant for | isolated chromophore

Question 53

what is conjugation?

Answer 53

when the π character spreads out over carbon chain

Question 54

what do conjugated systems do?

Answer 54

change energy between highest π MO and lowest π* MO

Question 55

more conjugated bonds means?

Answer 55

less energy needed for transition.

Question 56

if energy for transition is lower than?

Answer 56

wavelength increases (red shift)

Question 57

more conjugated the system the...

Answer 57

smaller the gap between π and π* , leading to larger wavelegnth

Question 58

white powders only absorb in the?

Answer 58

UV region not coloured

Question 59

molecules with N--N?

Answer 59

shot absorption into visible section by reducing pie to pie star gap.

Question 60

what are molecules with N--N called?

Answer 60

Azo compound

Question 61

Azo compound are used as?

Answer 61

dyes

Question 62

what are Sudan dyes?

Answer 62

used as food colouring

Question 63

UV-Visible spectroscopy can be used with?

Answer 63

- Presumptive tests - Fibres - Dyes - Inks - Paints

Question 64

is Uv vis destructive?

Answer 64

partially

Question 65

Microspectrophotometry..

Answer 65

is the new major technique

Question 66

what san issue with Microspectrophotometry?

Answer 66

difficult to find the perfect spot of sample.