Instrumental analysis questions with verified
answers
Absorbance of Beer's Law Ans✓✓✓ -log(T)=log( I/I0)
absorbance spectroscopy relationship to Beer's Law Ans✓✓✓ -This
relationship is the basis of all quantitative work in absorbance
spectroscopy.
-It allows one to determine the concentration of an absorbing species
simply by measuring its absorbance.
absorption filters Ans✓✓✓ -dye impregnated glass on other material
-single absorption, Beer's Law works A=Ebc
-T=I/I0
-%T tends to be low
-used with fluorescence
allowed transitions Ans✓✓✓ -must involve the promotion of electrons
without a change in their spin (or the # of unpaired electrons)
assumptions to be careful of: Ans✓✓✓ 1)molar absorptivity- not
constant, the molar absorptivity depends on instrumental conditions
and the solvent conditions
,2)the wavelength of lambda max- not a constant, solvent conditions
must be known, polar solvents result in a shift of the lambda max to
longer wavelengths, nonpolar solvents shift to short wavelengths
averaging Ans✓✓✓ -measuring current-high light levels(lots of
photons)
-a lot of electrons traveling --> gives you a current=averaging
bandpass Ans✓✓✓ -a characteristic of the instrument that effects the
bandwidth
-Filter that can be used to isolate or filter out certain frequencies that
lie within a particular band or range of frequencies
-1/10 the bandwidth
bandwidth Ans✓✓✓ -compound +conditions
-refer to picture
Beer's Lambert Law assumptions: Ans✓✓✓ 1) incident radiation is
monochromatic (1 wavelength)- (molar absorptivity is single valued)
2)uniform cross section- (b is single valued)
3) absorption of a substance (absorber) is independent of the presence
of other absorbers- ( abs total= abs1 + abs2 + abs3)
Beer's Lambert Law Ans✓✓✓ log(I/I0)=Ebc
, Beer's Law Ans✓✓✓ A=abc
where: A is absorbance
a describes the ability of a molecule to absorb radiation at a particular
wavelength.
b is the length of sample through which the light beam passes.
c is the concentration of the absorbing species.
chemical limitations Ans✓✓✓ a)chemical effect
-self interaction at high concentrations which makes molar absorptivity
a function of concentration
-deviation from linearity at high concentrations-refer to graphs
b)shifting equilibria
-ex: dichromate -->dilution --> chromate
-absorb at different colors: dichromate=orange, chromate=yellow
chemiluminescence Ans✓✓✓ -excitation results from a chemical
reaction
chromophore Ans✓✓✓ -an atom or group whose presence is
responsible for the color of a compound.
-Visible light that hits the chromophore can thus be absorbed by
exciting an electron from its ground state into an excited state.
answers
Absorbance of Beer's Law Ans✓✓✓ -log(T)=log( I/I0)
absorbance spectroscopy relationship to Beer's Law Ans✓✓✓ -This
relationship is the basis of all quantitative work in absorbance
spectroscopy.
-It allows one to determine the concentration of an absorbing species
simply by measuring its absorbance.
absorption filters Ans✓✓✓ -dye impregnated glass on other material
-single absorption, Beer's Law works A=Ebc
-T=I/I0
-%T tends to be low
-used with fluorescence
allowed transitions Ans✓✓✓ -must involve the promotion of electrons
without a change in their spin (or the # of unpaired electrons)
assumptions to be careful of: Ans✓✓✓ 1)molar absorptivity- not
constant, the molar absorptivity depends on instrumental conditions
and the solvent conditions
,2)the wavelength of lambda max- not a constant, solvent conditions
must be known, polar solvents result in a shift of the lambda max to
longer wavelengths, nonpolar solvents shift to short wavelengths
averaging Ans✓✓✓ -measuring current-high light levels(lots of
photons)
-a lot of electrons traveling --> gives you a current=averaging
bandpass Ans✓✓✓ -a characteristic of the instrument that effects the
bandwidth
-Filter that can be used to isolate or filter out certain frequencies that
lie within a particular band or range of frequencies
-1/10 the bandwidth
bandwidth Ans✓✓✓ -compound +conditions
-refer to picture
Beer's Lambert Law assumptions: Ans✓✓✓ 1) incident radiation is
monochromatic (1 wavelength)- (molar absorptivity is single valued)
2)uniform cross section- (b is single valued)
3) absorption of a substance (absorber) is independent of the presence
of other absorbers- ( abs total= abs1 + abs2 + abs3)
Beer's Lambert Law Ans✓✓✓ log(I/I0)=Ebc
, Beer's Law Ans✓✓✓ A=abc
where: A is absorbance
a describes the ability of a molecule to absorb radiation at a particular
wavelength.
b is the length of sample through which the light beam passes.
c is the concentration of the absorbing species.
chemical limitations Ans✓✓✓ a)chemical effect
-self interaction at high concentrations which makes molar absorptivity
a function of concentration
-deviation from linearity at high concentrations-refer to graphs
b)shifting equilibria
-ex: dichromate -->dilution --> chromate
-absorb at different colors: dichromate=orange, chromate=yellow
chemiluminescence Ans✓✓✓ -excitation results from a chemical
reaction
chromophore Ans✓✓✓ -an atom or group whose presence is
responsible for the color of a compound.
-Visible light that hits the chromophore can thus be absorbed by
exciting an electron from its ground state into an excited state.
