L5 Rich: uv-visible spectroscopy Flashcards Preview

1st Year sem 2 : Forensic Analysis > L5 Rich: uv-visible spectroscopy > Flashcards

Flashcards in L5 Rich: uv-visible spectroscopy Deck (66):
1

when reds absorbed what's wavelength and transmitted colour?

700-620
green

2

when orange absorbed what's wavelength and transmitted colour?

620-580
blue

3

when yellow absorbed what's wavelength and transmitted colour?

580-560
violet

4

when greens absorbed what's wavelength and transmitted colour?

560-490
red

5

when blue absorbed what's wavelength and transmitted colour?

490-430
orange

6

when violet absorbed what's wavelength and transmitted colour?

430-380
yellow

7

what part can the human see?

the UV Vis region

8

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

no

9

what does Uv vis tell us about?

quantity, absorption maximum.

10

what does a commercial spectrophotometer over?

185 –900 nm range

11

with a commercial spectrophotometer where can you get interference?

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

12

what is the origin absorption of Electronic Spectroscopy of Molecules?

Interaction of photons with ions or molecules

13

what happens when a molecule absorbs a photon ?

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

14

Does UV vis cause a change in vibrational energy?

no that happens in Raman spectroscopy

15

what does the change in electronic energy levels cause?

Results in alteration of vibrational and rotational energy

16

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

10,000 wave numbers in energy

17

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

mainly broad peaks
(covers multiple peaks occurring ta the same time)

18

absorption of photons takes how long?

10-18 s

19

in uv vis what stem axis of the graph

wavelength, transmittance/absorbance/reflectance

20

what stem units of wavelength?

nm

21

what is transmittance?

measure of intensities of transmitted and incident light

22

in ramane and infrared the x axis is in?

wavenumber

23

what's transmittance equation?

I/i0

24

what happens when UV vis is does on gases?

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

25

For Uv vis whats the sample prep?

- dissolve sample into solution

26

what can uV vis be done on?

gas liquid and solid

27

water has a maximum absorption wavelength of?

190nm ( in UV)

28

polar solid will need a ?

polar solvent

29

when preparing for Uv vis you need to know?

the concentration

30

cuvettes come in?

Quartz or glass or plastic

31

is glass cuvettes used during UV?

no use quartz

32

when using organic solvents, don't use?

plastic cuvette

33

what's the beer lambert law equation?

A=ecl

34

what is A?

absorbance

35

what's E?

molar absorption coefficient
dm3 mol-1 cm-1

36

what's c?

concentration in mol dm-3

37

what's l?

path length in cm (usually 1 )

38

what do you plot?

C against A (straight diagonal line)

39

whats the other equation?

A= - log 10T

T=10^-A

40

Uv vis spectroscopy mainly uses ?

organic compounds

41

How many transmissions do we need to know?

2 transmissions

42

what are the 2 transmissions?

n →π*
and
π→π*

43

n →π*

n electron to lowest π* anti bonding orbital

44

when does n →π* happen?

heteroatom with lone pair of electrons

45

π→π*

highest π orbital to lowest π* anti bonding orbital.

46

which has a more intense peak?

π→π*

47

which has a small peak?

n →π*

48

in transition metal compounds what transition happens?

d → d

49

for d → d what do you need?

partially filled d orbitals

50

what colour is chlorophyll?

green

51

what are chromophore groups functional for?

Functional groups responsible for absorption

52

what happens to the band of a chromophore group ?

Position and intensity of absorption band constant for
isolated chromophore

53

what is conjugation?

when the π character spreads out over carbon chain

54

what do conjugated systems do?

change energy between highest π MO and lowest π* MO

55

more conjugated bonds means?

less energy needed for transition.

56

if energy for transition is lower than?

wavelength increases (red shift)

57

more conjugated the system the...

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

58

white powders only absorb in the?

UV region not coloured

59

molecules with N--N?

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

60

what are molecules with N--N called?

Azo compound

61

Azo compound are used as?

dyes

62

what are Sudan dyes?

used as food colouring

63

UV-Visible spectroscopy can be used with?

- Presumptive tests
- Fibres
- Dyes
- Inks
- Paints

64

is Uv vis destructive?

partially

65

Microspectrophotometry..

is the new major technique

66

what san issue with Microspectrophotometry?

difficult to find the perfect spot of sample.