Deck 20: Applications of Spectrophotometry

Question 1

Sequential injection differs from flow injection by:

A)flow programming.
B)flow reversal.
C)reagent mixing.
D)flow reversal and reagent mixing.
E)flow programming and flow reversal.

Answer 1

flow programming and flow reversal.

Question 2

The method of continuous variation was applied to the complex formed between P and X.A plot of mole fraction X versus P_aX_b absorbance is plotted.What is the stoichiometry for the complex?

A)P₂X₃
B)PX₄
C)PX₅
D)P₃X₂
E)P₄X

Answer 2

PX₄

Question 3

A student determines the concentration chloride in an unknown sample by pipetting 10 mL of the sample and 10 mL of 1.000 × 10⁻⁵ M quinine solution to a 100 mL flask and diluting to volume with 1 M H₂SO₄.A series of six chloride standards were prepared using a 0.0100 M standard chloride solution,adding an increasing volume of chloride to 100 mL volumetric flasks,in addition to 10 mL of 1.000 × 10⁻⁵ M quinine.Each solution was diluted to volume with 1 M H₂SO₄.Calculate the chloride concentration for the unknown using the collected fluorescence data and the Stern-Volmer graph below for the data.

Answer 3

0.01886 M Cl⁻

Question 4

Which is true for the relationship between quencher concentration and fluorescent intensity?

A)As quencher concentration increases,fluorescent intensity increases.
B)As quencher concentration decreases,fluorescent intensity decreases.
C)As quencher concentration increases,fluorescent intensity decreases.
D)As quencher concentration increases,fluorescent intensity remains constant.
E)As quencher concentration decreases,fluorescent concentration remains constant.

Question 5

The advantages of flow injection analysis include which of the following?
I the speed in sample analysis
II automation of solution handling
III reproducibility
IV low cost of analysis

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

Question 6

For the method of continuous variation,which is NOT true?

A)The method of continuous variation allows for the determination of stoichiometry of a complex.
B)Corrected absorbance is the measured absorbance for the complex less the absorbance for unreacted ligand and central metal.
C)Maximum absorbance is reached at the composition corresponding to the stoichiometry of the predominant complex.
D)The total concentration for various ratios of P and X must be constant.
E)Maximum absorbance when the mole fraction X equals 0.75 is indicative of a complex with the chemical formula of PX₃.

Question 7

________________________________________enhances the fluorescence of immunoassays by a factor of 100 by measuring the fluorescence of Eu³⁺ 200 s after excitation with a laser pulse.

A)Time-resolved fluorescence immunoassays
B)Time-dependent fluorescence immunoassays
C)Immunoassay fluorescence over time immunoassays
D)Weakly bound time fluorescence immunoassays
E)Europium-bound fluorescence immunoassays

Question 8

For the acid-base indicator bromothymol blue,the protonated form,HBB,is yellow and the deprotonated form,BB⁻,is blue.When both forms are present the indicator has a green color,the shade of green depends on the ratio of HBB:BB⁻.Use the information below to calculate the concentration of HBB and BB⁻ for a green solution of bromothymol blue.

Question 9

Which is NOT true for a Scatchard plot?

A)A Scatchard plot is a graph of [PX]/[X] versus [PX].
B)

C)The binding constant,K,is the absolute value for the reciprocal of the slope.
D)

E)

Question 10

The stoichiometry for the complex MX_n is investigated using the method of continuous variation.A series of 11 solutions are prepared using 0.0100 molar M and 0.0100 molar X with the volumes in the table below.Use the standard solution composition and corrected absorbance data to determine the stoichiometry for the complex.Assume that the absorbance is due only to the complex.Include a rough graph to support your answer.

Question 11

The Stern-Volmer equation relates quencher concentration to the ratio ₀/_Q.Which of the following is NOT true for the Stern-Volmer equation?

A)The y-intercept for the Stern-Volmer equation is always 1.
B)The x-intercept for the Stern-Volmer equation is always 1.
C)The slope for the graph of quencher concentration versus I₀/I_Q is m =

)
D)I₀/I_Q is proportional to ₀/_Q.
E)(₀/_Q is greater than 1 for any concentration Q.)

Question 12

Which is true for spectroscopy of a mixture?

A)The absorbance for a mixture at a particular wavelength is the sum of the absorbances for the components that absorb at the particular wavelength.
B)Spectrophotometers can differentiate between mixture components that absorb at the same wavelength.
C)Each component in a mixture has the same molar absorptivity at the same wavelength.
D)The concentration for each component in the mixture is easily calculated with a set of simultaneous equations if there is significant overlap of individual spectra.
E)The concentration for each component in a mixture is easily calculated by least squares for guesses of each component when the individual spectra are well resolved.

Question 13

The technique in which a liquid sample is injected into a continuously flowing liquid carrier containing a reagent that reacts with the sample is called:

A)flow analysis.
B)sequential flow analysis.
C)sequential analysis.
D)sequential injection analysis.
E)flow injection analysis.

Question 14

When a molecule absorbs a photon,the molecule is promoted to an excited state,M^*.The rate at which M^* is created is proportional to the concentration of M.There are three pathways that M^* may take to return to the ground state.Which statement below is INCORRECT for these three pathways.

A)The rate at which the excited state returns to the ground state is independent of the pathway to the ground state and the concentration of excited state molecules.
B)The three possible pathways to return to the ground state are emission,deactivation,and quenching.
C)Quenching occurs when a second molecule,the quencher Q,collides with M^* to return M^* to the ground state.M^* + Q → M + Q^*
D)Deactivation returns M^* to the ground state by colliding with other molecules and releasing energy in the form of heat.M^* → M + heat
E)Emission returns M^* to the ground state by emitting a photon.M^* → M + hv.

Question 15

For the plot of absorbance versus wavelength for two compounds,which two wavelengths are most suited for mixture analysis?

A)515 nm,515 nm
B)445 nm,635 nm
C)380 nm,750 nm
D)515 nm,635 nm
E)445 nm,515 nm

Question 16

The advantages of sequential injection over flow injection analysis include all of the following,except:
I less waste generated.
II smaller volumes of expensive reagents are consumed.
III ability to handle large number of samples.
IV larger reaction volumes.

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

Question 17

An oxygen sensor is constructed from a fluorescent dye that is easily quenched by oxygen.The sensor is calibrated with a deoxygenated water sample and an oxygen saturated water sample,2.6 x 10⁻⁴ M.The sensor is deployed to a waste treatment plant to monitor dissolved oxygen in effluent.If the sensor records a fluorescent intensity of 322.928,what is the oxygen concentration?

Question 18

Which of the following is true for ELISA?
I An antibody,antibody 1,specific to the analyte of interest is dissolved in aqueous solution.
II Analyte is incubated with antibody 1,binding to form a complex.The fraction of antibody 1 sites bound to analyte is proportional to the concentration.
III Unbound substances are flushed from the ELISA surface and a second antibody,antibody 2,which binds to a different region of the analyte,is applied to the antibody 1-analyte complexes.
IV Antibody 2 is chemically modified to include an enzyme that converts a colorless reagent to a colored reagent.The more bound analyte,the more intense the color generated.

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

Question 19

The Scatchard plot for the reaction P + X ⇋ PX is below.What is the equilibrium constant for the reaction?

A)3)830 M⁻¹
B)1)478 × 10⁻⁴ M⁻¹
C)0)2611 M⁻¹
D)6765 M⁻¹
E)0)5832 M⁻¹

Question 20

For the UV-Vis absorption data below,calculate the concentration for the metals M²⁺ and N²⁺ in a river sample if the unknown solution was prepared by diluting 10.00 mL of river water with 10.00 mL of ligand solution and diluted to a final volume of 100.00 mL.Assume the absorbance was measured in a 1.00-cm cell.