Ch. 13 Instrumental Analysis questions with
verified answers
4 limitations to beer's law Ans✓✓✓ 1. concentration effects
2. chemical deviations
3. polychromatic radiation (instrumental)
4. presence of stray radiation (instrumental)
4 types of spectrometric instruments Ans✓✓✓ 1. single beam
2. double beam in space
3. double beam in time
4. multichannel
absorbance Ans✓✓✓ A=-log(P/Po)
beer's law Ans✓✓✓ A=ebc
- e is the molar absorbtivity (L/mol cm)
- b is the path length of the cuvette in which the sample is contained
(cm)
- c is the concentration of the compound in solution (mol/L)
Beer's law effectively states that the relationship between the
absorbance of a solution and the concentration of the absorbing
species in a solution is linear. This relationship is most likely to fail
, when: Ans✓✓✓ the absorbing species participates in a concentration-
dependent chemical equilibrium
chemical deviations of beer's law Ans✓✓✓ - *in many cases an analyte
dissociates or reacts to produce a product with a different absorption
spectrum than the analyte*
ex: the equilibrium of an indicator dye
Hln <-> H+ + ln-
- different concentrations of dye were dissolved in 0.1M HCl, beer's law
would be observed at 570nm for Hln
- different concentrations of dye were dissolved in 0.1M NaOH, beer's
law would be observed at 430nm for ln-
- at intermediate pH values, beer's law isn't followed for either 430 or
570nm
- position of the dissociation equilibrium is a function of concentration
Hln <-> H+ + ln-
- percent ionization increases as concentration decreases
concentration effects of beer's law Ans✓✓✓ - beer's law is only valid
to the absorption of media containing low analyte concentrations (<
0.01M)
- it is a "limiting law", not really valid at all concentrations
- when [A] > 0.01M solute-solute interactions can affect analyte photo-
physical properties
verified answers
4 limitations to beer's law Ans✓✓✓ 1. concentration effects
2. chemical deviations
3. polychromatic radiation (instrumental)
4. presence of stray radiation (instrumental)
4 types of spectrometric instruments Ans✓✓✓ 1. single beam
2. double beam in space
3. double beam in time
4. multichannel
absorbance Ans✓✓✓ A=-log(P/Po)
beer's law Ans✓✓✓ A=ebc
- e is the molar absorbtivity (L/mol cm)
- b is the path length of the cuvette in which the sample is contained
(cm)
- c is the concentration of the compound in solution (mol/L)
Beer's law effectively states that the relationship between the
absorbance of a solution and the concentration of the absorbing
species in a solution is linear. This relationship is most likely to fail
, when: Ans✓✓✓ the absorbing species participates in a concentration-
dependent chemical equilibrium
chemical deviations of beer's law Ans✓✓✓ - *in many cases an analyte
dissociates or reacts to produce a product with a different absorption
spectrum than the analyte*
ex: the equilibrium of an indicator dye
Hln <-> H+ + ln-
- different concentrations of dye were dissolved in 0.1M HCl, beer's law
would be observed at 570nm for Hln
- different concentrations of dye were dissolved in 0.1M NaOH, beer's
law would be observed at 430nm for ln-
- at intermediate pH values, beer's law isn't followed for either 430 or
570nm
- position of the dissociation equilibrium is a function of concentration
Hln <-> H+ + ln-
- percent ionization increases as concentration decreases
concentration effects of beer's law Ans✓✓✓ - beer's law is only valid
to the absorption of media containing low analyte concentrations (<
0.01M)
- it is a "limiting law", not really valid at all concentrations
- when [A] > 0.01M solute-solute interactions can affect analyte photo-
physical properties
