UV-Vis Spectroscopy

Question 1

UV-Vis Transitions

Answer 1

bonding to antibonding
sigma to sigma*
pie to pie*

nonbonding to antibonding
n to sigma*
n to pie*

Question 2

Forbidden UV-Vis Transitions

Answer 2

sigma to pie*
pie to sigma*

Question 3

Lowest to highest energy
pie, sigma, sigma, pie, n

Answer 3

sigma, pie, n, pie, sigma

Question 4

Functional groups that absorb in the UV and Vis regions

Answer 4

Chromophores

Question 5

functional groups that do not absorb in the UV and Vis region but have effect of shifting chromophore peaks to different wavelengths

Answer 5

Auxochromes

Question 6

absorbing species that shared pi and sigma electrons, unshared outer electrons

Answer 6

organic compounds

Question 7

absorbing species which have unfilled d and f orbitals

Answer 7

inorganic species

Question 8

Type of Shifts

Answer 8

Bathochromic
Hypsochromic
Hyperchromic
Hypochromic

Question 9

shift in lamba max to longer wavelength

Answer 9

bathochromic shift

Question 10

shift in lamba max to shorter wavelength

Answer 10

hypsochromic shift

Question 11

increase in the intensity of UV maxima

Answer 11

hyperchromic shift

Question 12

decrease in intensity of UV maxima

Answer 12

hypochromic shift

Question 13

Basic Instrumentation (UV-Vis)

Answer 13

Radiation Source
Wavelength Selector
Sample Holder
Detector
*Computer for signal processing and output

Question 14

Common Radiation Source for UV-Vis

Answer 14

Deuterium arc lamp
Tungsten halogen lamp

Question 15

radiation source that emits in one direction only and had a half-life; common for UV

Answer 15

deuterium arc lamp

Question 16

Radiation source common for Vis; polychromatic light is required; low noise

Answer 16

Tungsten Halogen Lamp

Question 17

Device that uses filter as wavelength selector; for visible region; single wavelength

Answer 17

Photometer

Question 18

Uses monochromator as wavelength selector; multiple wavelength; for UV-Vis region (occ for IR)

Answer 18

Spectrometer/ Spectrophotometer

Question 19

small tube-like container with straight sides and a square cross-section

Answer 19

cuvette

Question 20

distance of light that goes through the interior walls of a cuvette; inner distance from front to back window

Answer 20

Cuvette Path Length

Question 21

Standard Cuvette Path Length

Answer 21

10mm

Question 22

Lowest in cost cuvette; not resistant to all solvents; for Vis region only

Answer 22

acrylic plastic cells

Question 23

Type of cell that is slightly more expensive than acrylic cells ; used in visible region only

Answer 23

Silicate glass cells

Question 24

type of cuvette characterized for being very expensive; used for both UV and Vis region

Answer 24

Fused quartz cells

Question 25

type of cell that can be used when sample volume is extremely limited (5microL)

Answer 25

microcells

Question 26

The loss of sensitivity of microcells depends on the ____ and __

Answer 26

degree of aperturing and optical geometry

Question 27

Do not touch the ____ with fingers, as oil can cause ___

Answer 27

optical surface; significant absorbance

Question 28

If optical surfaces get mild contamination, the cell can be wiped with ___

Answer 28

photographic tissue

Question 29

Remedy for serious contamination of optical surface

Answer 29

Using mild sulfonic detergent

Question 30

Remedy for severe contamination of optical surfaces

Answer 30

Treatment with hydrochloric acid or nitric acid

Question 31

Spectrophotometers usually contain either ___ or ___ detector

Answer 31

photomultiplier tube or photodiode detector

Question 32

contain several photodiode detectors instead of a single one

Answer 32

photodiode array

Question 33

Types of instruments (UV-Vis)

Answer 33

Single-beam Double-beam in space Double-beam in time multichannel

Question 34

type of instrument where there is only one light beam or optical path from source to detector

Answer 34

Single-beam

Question 35

two beams are formed in space by a V-shape mirror called beamsplitter simultaneously

Answer 35

double-beam in space

Question 36

beams are separated in time by a rotating sector mirror that directs the entire beam from monochromator first through the reference cell and then the sample cell alternately

Answer 36

double-beam in time

Question 37

type of instrument that able to scan an entire spectrum in 0.1 seconds

Answer 37

multichannel

Question 38

Problems in Measurement (UV-Vis)

Answer 38

Strong Absorbance Weak Absorbance Interference Sample Decomposition

Question 39

Remedy for strong Absorbance

Answer 39

dilute sample to an absorbance level within the linear dynamic range

Question 40

Reducing the noise level will?

Answer 40

directly improves the precision of results

Question 41

Increasing slit width will?

Answer 41

Allow more light, reduce the noise level, and improves the precision of results

Question 42

Types of interference

Answer 42

Scattering Fluorescence

Question 43

Scattering effect can be reduced by?

Answer 43

placing the sample as close as possible to detector

Question 44

Types of scattering

Answer 44

Rayleigh Tyndall

Question 45

occurs when the particles are small relative to the wavelength of light and is inversely proportional to the fourth power of wavelength

Answer 45

Rayleigh scattering

Question 46

occurs when the particles are large relative to wavelength of light and is inversely proportional to the square of wavelength

Answer 46

Tyndall scattering

Question 47

____ in the light can eliminate the error due to fluorescence

Answer 47

Placing a filter

Question 48

How to prevent sample decomposition?

Answer 48

Placing a filter to eliminate low-wavelength UV light

Question 49

Qualitative Analysis (UV-Vis) (4)

Answer 49

Detection of Impurities Detection of Isomers Detection of Functional Groups Determination of MW

Question 50

Quantitative Analysis

Answer 50

Determination of Concentration Multicomponent Analysis Spectrophotometric Titration

Question 51

UV wavelength range

Answer 51

200-380 nm

Question 52

Visible Light wavelength range

Answer 52

380 - 800 nm