Question 1

Which of the following is TRUE for excitation spectra?

Accepted Answer

A)  Excitation wavelength is fixed and the emission wavelengths are scanned.
B)  Excitation wavelength is scanned and the emission wavelength is fixed.
C)  Excitation wavelength is fixed and the emission wavelength is fixed.
D)  Excitation wavelength is scanned and the emission wavelength is scanned.
E)  None of these answers is true. B

Question 2

A 10.00 mL sample is titrated with 0.50 mL of titrant.The observed absorbance is 0.3219.Calculate the corrected absorbance.

Accepted Answer

A)  0) 3066
B)  0) 3058
C)  0) 2912
D)  0) 3380
E)  0) 3558 D

Question 3

After 10.00 mL titrant has been added to 50.00 mL analyte the absorbance was measured to be 0.4639.Calculate corrected absorbance.

Accepted Answer

0.5567

Question 4

All of the following are TRUE for luminescence,except:

Accepted Answer

A)  luminescence is emission of light from an excited state of a molecule.
B)  luminescence is inherently more sensitive than absorption.
C)  at low concentration,emission intensity is proportional to analyte concentration.
D)  at high concentration,emission intensity decreases due to dilution.
E)  light emitted from a chemical reaction is called chemiluminescence.

Question 5

Which of the following is NOT true for light modeled as a particle?

Accepted Answer

A)  A particle of light is the photon.
B)  The energy of a photon is proportional to the photon's frequency.
C)  Wavenumber is inversely proportional to photon energy.
D)  As the wavelength increases,photon energy decreases.
E)  The product of frequency and Planck's constant equals photon energy.

Question 6

Which of the following are correct for Beers Law?
I Absorbance increases as concentration increases.
II Absorbance decreases as pathlength increases.
III The molar absorptivity value is chromophore and wavelength specific.
IV The absorption spectrum is a graph showing absorbance changes with wavelength.

Accepted Answer

A)  I,II,and III
B)  1,III,and IV
C)  II,III,and IV
D)  I and III
E)  I,II,III,and IV

Question 7

The iron content of a well water sample must be quantified.A 10.00 mL aliquot of well water is transferred to a 100.0-mL volumetric flask and 20 mL of 0.10 M nitric acid is added to oxidize iron(II)to iron(III).Next 30 mL of a 0.1 M sodium thiocyanate solution is added to form the deep red complex iron(III)thiocyanate.The solution is diluted to volume with distilled deionized water.A reagent blank is similarly prepared.If the absorbance of the iron thiocyanate solution is 0.5483 and the reagent blank absorbance is 0.0282,calculate the iron concentration for the water sample.The molar absorptivity for iron(III)thiocyanate is 3200 M⁻¹ cm⁻¹.Assume a pathlength of 1 cm and a 100% yield. Fe³⁺ (aq)+ SCN^- (aq)____________________ FeSCN²⁺ (aq)

Accepted Answer

The answer of The iron content of a well water...

Question 8

Which of the statements below is FALSE for the excited and ground states of molecules?

Accepted Answer

A)  Electron spins are opposed in the singlet,S0,excited state.
B)  Electron spins are parallel in the triplet,T1,excited state.
C)  Electrons release energy when transitioning from the S1 to the S0 state.
D)  Electrons gain energy when transitioning from the S0 to the S1 state.
E)  Molecular geometry in the excited state may be different than the molecular geometry in the ground state.

Question 9

A transmittance of 0.3847 is measured for a 0.00023 M solution.Assuming a pathlength of 1 cm,calculate the molar absorptivity of the solute.

Accepted Answer

The answer of A transmittance of 0.3847 is measured for...

Question 10

Quinine sulfate in 0.5 M sulfuric acid is excited at 310 nm and fluoresces at 450 nm.How many Joules were dissipated through nonradiative transitions on a per molecule basis?

Accepted Answer

The answer of Quinine sulfate in 0.5 M sulfuric acid...

Question 11

Beer's law works for____________________ radiation passing through a____________________ solution in which the absorbing species is____________________ in a concentration-dependent equilibrium.

Accepted Answer

A)  polychromatic ;dilute ;not participating
B)  monochromatic;concentrated;not participating
C)  monochromatic;concentrated;participating
D)  polychromatic ;dilute ;participating
E)  monochromatic;dilute;not participating

Question 12

Which of the following is NOT true for light modeled as a wave?

Accepted Answer

A)  Frequency is the number of waves that pass a given point in 1 second.
B)  Wavelength is the distance between the crest and the trough.
C)  Light travels slower through matter than a vacuum.
D)  In a vacuum the speed of light is 3.0 × 108 m/s.
E)  The product of a waves frequency and wavelength is the speed of light.

Question 13

Phosphorescence is:

Accepted Answer

A)  a nonradiative transition between states with the same spin,S1  S0.
B)  a nonradiative transition between states with different spin,T1  S0
C)  the emission of a photon during a transition between states with the same spin,S1  S0.
D)  the emission of a photon during a transition between states with different spin,T1  S0
E)  None of these answers defines phosphorescence.

Question 14

The basic spectrophotometer is composed of four components.Which component listed below is NOT one of the four?

Accepted Answer

A)  sample
B)  monochromator
C)  beam splitter
D)  light source
E)  light detector

Question 15

Which of the following is TRUE for emission spectra?

Accepted Answer

A)  Excitation wavelength is fixed and the emission wavelengths are scanned.
B)  Excitation wavelength is scanned and the emission wavelength is fixed.
C)  Excitation wavelength is fixed and the emission wavelength is fixed.
D)  Excitation wavelength is scanned and the emission wavelength is scanned.
E)  None of these answers is true.

Question 16

The part of a spectrophotometer that selects the wavelength to irradiate the sample is called the:

Accepted Answer

A)  polychromator.
B)  monochromator.
C)  beam splitter.
D)  light source.
E)  optode.

Question 17

Absorbance measured during a spectrophotometric titration must be corrected due to

Accepted Answer

A)  absorbing wavelength changes over time.
B)  dilution of the analyte by titrant.
C)  contaminants in the titrant.
D)  instrument drift.
E)  decomposition of analyte.

Question 18

Fluorescence is:

Accepted Answer

A)  a nonradiative transition between states with the same spin,S1  S0.
B)  a nonradiative transition between states with different spin,T1  S0
C)  the emission of a photon during a transition between states with the same spin,S1  S0.
D)  the emission of a photon during a transition between states with different spin,T1  S0
E)  None of these answers defines fluorescence.

Question 19

Calculate the energy of a photon with a frequency of 573.8 nm.

Accepted Answer

A)  3) 46 x 10−37 J
B)  3) 80 x 10−40 J
C)  3) 46 x 10−28 J
D)  3) 80 x 10−31
E)  3) 46 x 10−19 J

Question 20

Reagent blanks are primarily used to:

Accepted Answer

A)  align the optics to achieve maximum irradiance.
B)  compensate for any absorbance due to reagents or contamination.
C)  verify reagent purity.
D)  calibrate the spectrophotometer.
E)  test detector sensitivity.

Exam 19: Fundamentals of Spectrophotometry