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

L5 Rich: uv-visible spectroscopy Flashcards

1
Q

when reds absorbed what’s wavelength and transmitted colour?

A

700-620

green

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2
Q

when orange absorbed what’s wavelength and transmitted colour?

A

620-580

blue

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3
Q

when yellow absorbed what’s wavelength and transmitted colour?

A

580-560

violet

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4
Q

when greens absorbed what’s wavelength and transmitted colour?

A

560-490

red

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5
Q

when blue absorbed what’s wavelength and transmitted colour?

A

490-430

orange

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6
Q

when violet absorbed what’s wavelength and transmitted colour?

A

430-380

yellow

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7
Q

what part can the human see?

A

the UV Vis region

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8
Q

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

A

no

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9
Q

what does Uv vis tell us about?

A

quantity, absorption maximum.

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10
Q

what does a commercial spectrophotometer over?

A

185 –900 nm range

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11
Q

with a commercial spectrophotometer where can you get interference?

A

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

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12
Q

what is the origin absorption of Electronic Spectroscopy of Molecules?

A

Interaction of photons with ions or molecules

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13
Q

what happens when a molecule absorbs a photon ?

A

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

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14
Q

Does UV vis cause a change in vibrational energy?

A

no that happens in Raman spectroscopy

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15
Q

what does the change in electronic energy levels cause?

A

Results in alteration of vibrational and rotational energy

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16
Q

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

A

10,000 wave numbers in energy

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17
Q

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

A

mainly broad peaks

covers multiple peaks occurring ta the same time

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18
Q

absorption of photons takes how long?

A

10-18 s

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19
Q

in uv vis what stem axis of the graph

A

wavelength, transmittance/absorbance/reflectance

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20
Q

what stem units of wavelength?

A

nm

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21
Q

what is transmittance?

A

measure of intensities of transmitted and incident light

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22
Q

in ramane and infrared the x axis is in?

A

wavenumber

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23
Q

what’s transmittance equation?

A

I/i0

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24
Q

what happens when UV vis is does on gases?

A

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

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25
Q

For Uv vis whats the sample prep?

A
  • dissolve sample into solution
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26
Q

what can uV vis be done on?

A

gas liquid and solid

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27
Q

water has a maximum absorption wavelength of?

A

190nm ( in UV)

28
Q

polar solid will need a ?

A

polar solvent

29
Q

when preparing for Uv vis you need to know?

A

the concentration

30
Q

cuvettes come in?

A

Quartz or glass or plastic

31
Q

is glass cuvettes used during UV?

A

no use quartz

32
Q

when using organic solvents, don’t use?

A

plastic cuvette

33
Q

what’s the beer lambert law equation?

A

A=ecl

34
Q

what is A?

A

absorbance

35
Q

what’s E?

A

molar absorption coefficient

dm3 mol-1 cm-1

36
Q

what’s c?

A

concentration in mol dm-3

37
Q

what’s l?

A

path length in cm (usually 1 )

38
Q

what do you plot?

A

C against A (straight diagonal line)

39
Q

whats the other equation?

A

A= - log 10T

T=10^-A

40
Q

Uv vis spectroscopy mainly uses ?

A

organic compounds

41
Q

How many transmissions do we need to know?

A

2 transmissions

42
Q

what are the 2 transmissions?

A

n →π*
and
π→π*

43
Q

n →π*

A

n electron to lowest π* anti bonding orbital

44
Q

when does n →π* happen?

A

heteroatom with lone pair of electrons

45
Q

π→π*

A

highest π orbital to lowest π* anti bonding orbital.

46
Q

which has a more intense peak?

A

π→π*

47
Q

which has a small peak?

A

n →π*

48
Q

in transition metal compounds what transition happens?

A

d → d

49
Q

for d → d what do you need?

A

partially filled d orbitals

50
Q

what colour is chlorophyll?

A

green

51
Q

what are chromophore groups functional for?

A

Functional groups responsible for absorption

52
Q

what happens to the band of a chromophore group ?

A

Position and intensity of absorption band constant for

isolated chromophore

53
Q

what is conjugation?

A

when the π character spreads out over carbon chain

54
Q

what do conjugated systems do?

A

change energy between highest π MO and lowest π* MO

55
Q

more conjugated bonds means?

A

less energy needed for transition.

56
Q

if energy for transition is lower than?

A

wavelength increases (red shift)

57
Q

more conjugated the system the…

A

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

58
Q

white powders only absorb in the?

A

UV region not coloured

59
Q

molecules with N–N?

A

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

60
Q

what are molecules with N–N called?

A

Azo compound

61
Q

Azo compound are used as?

A

dyes

62
Q

what are Sudan dyes?

A

used as food colouring

63
Q

UV-Visible spectroscopy can be used with?

A
  • Presumptive tests
  • Fibres
  • Dyes
  • Inks
  • Paints
64
Q

is Uv vis destructive?

A

partially

65
Q

Microspectrophotometry..

A

is the new major technique

66
Q

what san issue with Microspectrophotometry?

A

difficult to find the perfect spot of sample.

1st Year sem 2 : Forensic Analysis (7 decks)

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