Question: The reduced form of nicotinamide adenine
The reduced form of nicotinamide adenine dinucleotide (NADH) is an important and highly fluorescent coenzyme. It has an absorption maximum of 340 nm and an emission maximum at 465 nm. Standard solutions of NADH gave the following fluorescence intensities: 
a) Construct a spreadsheet, and use it to draw a calibration curve for NADH. b) Find the least-squares slope and intercept for the plot in (a). c) Calculate the standard deviation of the slope and the standard deviation about regression for the curve. d) An unknown exhibits a relative fluorescence intensity of 11.34. Use the spreadsheet to calculate the concentration of NADH. e) Calculate the relative standard deviation for the result in part (d). f) Calculate the relative standard deviation for the result in part (d) if the reading of 12.16 was the mean of three measurements.
> Why is the working electrode normally isolated from the counter electrode in a controlled-potential coulometric analysis?
> What is the purpose of a depolarizer?
> What is meant by Nernstian behavior in an indicator electrode?
> How do electro gravimetric and coulometric methods differ from potentiometric methods? Consider currents, voltages, and instrumentation in your answer.
> What is a supporting electrolyte, and what is its role in electrochemistry?
> Describe conditions that favor kinetic polarization in an electrochemical cell.
> How do concentration polarization and kinetic polarization resemble one another? How do they differ?
> Quinone can be reduced to hydroquinone with an excess of electrolytically generated Sn(II): The polarity of the working electrode is then reversed, and the excess Sn(II) is oxidized with Br2 generated in a coulometric titration: Sn2+ + Br2 ( Sn4+ + 2Br-
> Traces of aniline, C6H5NH2, in drinking water can be determined by reaction with an excess of electrolytically generated Br2: The polarity of the working electrode is then reversed, and the excess Br2 is determined by a coulometric titration involving t
> Construct a coulometric titration curve of 100.0 mL of a 1 M H2SO4 solution containing Fe(II) titrated with Ce(IV) generated from 0.075 M Ce(III). The titration is monitored by potentiometry. The initial amount of Fe(II) present is 0.05182 mmol. A consta
> At a potential of −1.0 V (versus SCE), CCl4 in methanol is reduced to CHCl3 at a mercury cathode: 2CCl4 + 2H+ + 2e- + 2Hg(l) ( 2CHCl3 + Hg2Cl2(s) At -1.80 V, the CHCl3 further reacts to give CH4: 2CHCl3 + 6H+ + 6e- + 6Hg(l) ( 2CH4 + 3Hg
> The phenol content of water downstream from a coking furnace was determined by coulometric analysis. A 100-mL sample was rendered slightly acidic, and an excess of KBr was introduced. To produce Br2 for the reaction a steady current of 0.0703 A for 5 mi
> You need to choose between determining an analyte by measuring an electrode potential or by performing a titration. Explain which you would choose if you needed to know (a) The absolute amount of the analyte to a few parts per thousand. (b) The activity
> A fluoride electrode was used to determine the amount of fluoride in drinking water samples. The results given in the table that follows were obtained for four standards and two unknowns. Constant ionic strength and pH conditions were used. (a) Plot a c
> A lithium ion-selective electrode gave the potentials given next for the following standard solutions of LiCl and two samples of unknown concentration: (a) Construct a calibration curve of potential versus log aLi+, and determine if the electrode follow
> The F− concentration of a solution was determined by measurements with a liquid-membrane electrode. The electrode system developed a potential of 0.5021 V when immersed in 25.00 mL of the sample, and 0.4213 V after the addition of 2.00 mL of 5.45 x 10−2
> The Na+ concentration of a solution was determined by measurements with a sodium ion-selective electrode. The electrode system developed a potential of −0.2462 V when immersed in 10.0 mL of the solution of unknown concentration. After addition of 1.00 mL
> The titration of Fe(II) with permanganate yields a particularly asymmetrical titration curve because of the different number of electrons involved in the two half-reactions. Consider the titration of 25.00 mL of 0.1 M Fe(II) with 0 1. MMnO−4. The H+ conc
> A 40.00-mL aliquot of 0.05000 M HNO2 is diluted to 75.00 mL and titrated with 0 0800 MCe4+ The pH of the solution is maintained at 1.00 throughout the titration; the formal potential of the cerium system is 1.44 V. (a) Calculate the potential of the indi
> Calculate the potential of a silver indicator electrode versus the standard calomel electrode after the addition of 5.00, 15.00, 25.00, 30.00, 35.00, 39.00, 39.50, 36.60, 39.70, 39.80, 39.90, 39.95, 39.99, 40.00, 40.01, 40.05, 40.10, 40.20, 40.30, 40.40,
> A 0.4021-g sample of a purified organic acid was dissolved in water and titrated potentiometrically. A plot of the data revealed a single end point after 18.62 mL of 0.1243 M NaOH had been introduced. Calculate the molecular mass of the acid.
> The cell SCE||H+(a = x)| glass electrode has a potential of 0.2106 V when the solution in the right-hand compartment is a buffer of pH 4.006. The following potentials are obtained when the buffer is replaced with unknowns: (a) −0.2902V and (b) +0.1241V.
> The cell SCE||Ag2CrO4(sat'd), (x M)|Ag is used for the determination of pCrO4. Calculate pCrO4 when the cell potential is 0.389 V.
> Briefly describe or define a) Liquid junction potential. b) Boundary potential. c) Asymmetry potential. d) Combination electrode
> Why is atomic emission more sensitive to flame instability than atomic absorption?
> Define (a) Atomization. (b) Pressure broadening. (c) Doppler broadening. (d) Aerosol. (e) Plasma. (f) Nebulization. (g) Hollow-cathode lamp. (h) Sputtering. (i) Additive interference. (j) Ionization interference. (k) Chemical interference. (l) Radiation
> Describe the basic differences among atomic emission, atomic absorption, and atomic fluorescence spectroscopy.
> Lead was determined in a brass sample by atomic absorption and the method of standard additions. The original sample was dissolved and diluted to 50.0 mL. This solution was introduced into an AA spectrometer and an absorbance of 0.42 was obtained. To the
> Calculate (a) pI if the cell in Problem 19-17(a) has a potential of -196 mV. (b) pCl if the cell in Problem 19-17(b) has a potential of -0.137 V. (c) pPO4 if the cell in Problem 19-17(c) has a potential of 0.211 V. (d) pCN if the cell in Problem 19-17(d)
> The copper in an aqueous sample was determined by atomic absorption flame spectrometry. First, 10.0 mL of the unknown were pipetted into each of five 50.0-mL volumetric flasks. Various volumes of a standard containing 12.2 ppm Cu were added to the flasks
> The chromium in a series of steel samples was determined by ICP emission spectroscopy. The spectrometer was calibrated with a series of standards containing 0, 2.0, 4.0, 6.0, and 8.0 μg K2Cr2O7 per milliliter. The instrument readings for th
> A 5.00-mL sample of blood was treated with trichloroacetic acid to precipitate proteins. After centrifugation, the resulting solution was brought to pH 3 and extracted with two 5-mL portions of methyl isobutyl ketone containing the lead-complexing agent
> In the atomic absorption determination of uranium, there is a linear relationship between the absorbance at 351.5 nm and concentration from 500 to 2000 ppm of U. At concentrations much lower than 500 ppm, the relationship becomes nonlinear unless about 2
> Discuss the differences that result in ICP atomic emission when the plasma is viewed axially rather than radially.
> Why is the ICP rarely used for atomic absorption measurements?
> Name four characteristics of inductively coupled plasmas that make them suitable for atomic emission spectrometry.
> In flame AA with a hydrogen/oxygen flame, the absorbance for calcium decreases in the presence of large concentrations of phosphate ion. a) Suggest an explanation for this observation. b) Suggest three possible methods for overcoming the potential inte
> Why are the lines from a hollow-cathode lamp generally narrower than the lines emitted by atoms in a flame?
> Why are higher resolution monochromators found in ICP atomic emission spectrometers than in flame atomic absorption spectrometers?
> Generate an equation that relates pAnion to Ecell for each of the cells in Problem 19-17. Cells in Problem 19-17: (a) pI. (b) pCl. (c) pPO4. (d) pCN.
> Why is source modulation used in atomic absorption spectroscopy?
> Why are ionization interferences usually not as severe in the ICP as they are in flames?
> Why do some absorbing compounds show no fluorescence?
> Which compound in each of the following pairs would you expect to have a greater fluorescence quantum yield? Explain. a) b)
> Why are fluorescence methods potentially more sensitive than absorption methods?
> Briefly describe or define (a) Fluorescence. (b) Non-radiative relaxation. (c) Internal conversion. (d) Chemiluminescence. (e) Stokes shift. (f) Secondary absorption. (g) Inner-filter effect. (h) Triplet state.
> The determination in Problem 25-12 was modified to use the standard additions method. In this case, a 2.196-g tablet was dissolved in sufficient 0.10 M HCl to give 1.000 L. Dilution of a 20.00-mL aliquot to 100 mL produced a solution that gave a reading
> Quinine in a 1.664-g antimalarial tablet was dissolved in sufficient 0.10 M HCl to give 500 mL of solution. A 15.00-mL aliquot was then diluted to 100.0 mL with the acid. The fluorescence intensity for the diluted sample at 347.5 nm provided a reading of
> The volumes of a 1.10 ppm standard solution of Zn2+ shown in the following table were pipetted into separatory funnels each containing 5.00 mL of an unknown zinc solution. Each was extracted with three 5-mL aliquots of CCl4 containing an excess of 8-hydr
> Use the shorthand notation to describe a cell consisting of a saturated calomel reference electrode and a silver indicator electrode for the measurement of (a) pI. (b) pCl. (c) pPO4. (d) pCN.
> Why are fluorometers often more useful than spectrofluorometers for quantitative analysis?
> Why are phosphorescence lifetimes much longer than fluorescence lifetimes?
> Describe the components of a filter fluorometer and a spectrofluorometer.
> Explain why fluoresence emission often occurs at a longer wavelength than absorption.
> Describe the characteristics of organic compounds that fluoresce.
> What is(are) advantage(s) of the multiple standard additions method over the single-point standard addition method?
> What experimental variables must be controlled to assure reproducible absorbance data?
> What minimum requirement is needed to obtain reproducible results with a single-beam spectrophotom?
> Describe the differences between the following pairs of terms, and list any particular advantages of one over the other: a) Spectrophotometers and photometers. b) Single-beam and double-beam instruments for absorbance measurements. c) Conventional and
> Predict the shape of photometric titration curves (after correction for volume change) if—at the wavelength selected—the molar absorptivities for the analyte A, the titrant T, and the product P are as follows:
> a) Calculate E0 for the process b) Use the shorthand notation to describe a cell consisting of a Ag/AgCl reference electrode and a lead indicator electrode that could be used for the measurement of pCl. c) Generate an equation that relates the potential
> The equilibrium constant for the conjugate acid-base pair is 8.00 x 10-5. From the additional information a) Calculate the absorbance at 430 nm and 600 nm for the following indicator concentrations: 3.00 × 10-4 M, 2.00 × 10-4
> Estimate the frequencies of the absorption maxima in the IR spectrum of methylene chloride shown in Figure 24F-2. From these frequencies, assign molecular vibrations of methylene chloride to each of the bands. Notice that some of the group frequencies th
> Mercury(II) forms a 1:1 complex with triphenyltetrazolium chloride (TTC) that exhibits an absorption maximum at 255 nm.21 The mercury(II) in a soil sample was extracted into an organic solvent containing an excess of TTC, and the resulting solution was d
> Palladium(II) forms an intensely colored complex at pH 3.5 with arsenazo III at 660 nm.20 A meteorite was pulverized in a ball mill, and the resulting powder was digested with various strong mineral acids. The resulting solution was evaporated to dryness
> The accompanying absorption data were recorded at 390 nm in 1.00-cm cells for a continuous-variations study of the colored product formed between Cd2+ and the complexing reagent R. a) Find the ligand-to-metal ratio in the product. b) Calculate an avera
> The accompanying data were obtained in a slope-ratio investigation of the complex formed between Ni2+ and 1-cyclopentene-1-dithiocarboxylic acid (CDA). The measurements were made at 530 nm in 1.00-cm cells. a) Determine the formula of the complex. Use l
> The sodium salt of 2-quinizarinsulfonic acid (NaQ) forms a complex with Al3+ that absorbs strongly at 560 nm19. The data collected on this system are shown in the accompanying table. a) Find the formula of the complex from the data. In all solutions, cA1
> The method developed in Problem 24-26 was used for the routine determination of iron in 25.0-mL aliquots of ground water. Express the concentration (as ppm Fe) in samples that yielded the accompanying absorbance data (1.00-cm cell). Calculate the relativ
> A standard solution was put through appropriate dilutions to give the concentrations of iron shown in the accompanying table. The iron(II)-1,10,phenanthroline complex was then formed in 25.0-mL aliquots of these solutions, following which each was dilute
> Use the data in Problem 24-24 to calculate the molar concentration of P and Q in each of the following solutions: Data from Problem 24-24: Solutions of P and Q individually obey Beer’s law over a large concentration range. Spectral dat
> a) Calculate E0 for the process (b) Use the shorthand notation to describe a cell consisting of a saturated calomel reference electrode and a silver indicator electrode that could be used to measure pIO3. (c) Develop an equation that relates the potenti
> Solutions of P and Q individually obey Beer’s law over a large concentration range. Spectral data for these species in 1.00-cm cells are a) Plot an absorption spectrum for a solution that is 6.45 × 10-5M in P and 3.21 &Ati
> Constr uct an absorption spectr um for a 7.00 × 10-5 M solution of the indicator of Problem 24-19 when measurements are made with 1.00-cm cells and a) b) c) Incicator of Problem 24-19: Indicator HIn
> Several buffer solutions were made 1.00 x 10-4M in the indicator of Problem 24-19. Absorbance data (1.00-cm cells) are Calculate the pH of each solution. Indicator of Problem 24-19: Indicator HIn
> What is the absorbance at 595 nm (1.00-cm cells) of a solution that is 1.25 × 10-4M in the indicator of Problem 24-19 and has a pH of a) 5.30, b) 5.70, c) 6.10? Indicator of Problem 24-19: The indicator HIn
> Calculate the absorbance (1.00-cm cells) at 450 nm of a solution in which the total molar concentration of the indicator described in Problem 24-19 is 8.00 × 10-5M and the pH is a) 4.92, b) 5.46, c) 5.93, d) 6.16.
> The indicator HIn has an acid dissociation constant of 4.80 × 10-6 at ordinary temperatures. The accompanying absorbance data are for 8.00 × 10-5 M solutions of the indicator measured in 1.00-cm cells in strongly acidic and stro
> Molar absorptivity data for the cobalt and nickel complexes with 2,3-quinoxalinedithiol are εCo = 36,400 and εNi = 5520 at 510 nm and εCo = 1240 and εNi = 17,500 at 656 nm. A 0.425-g sample was dissolved and diluted to 50.0 mL. A 25.0-mL aliquot was trea
> A. J. Mukhedkar and N. V. Deshpande (Anal. Chem., 1963, 35, 47, DOI: 10.1021/ac60194a014) report on a simultaneous determination for cobalt and nickel based on absorption by their 8-quinolinol complexes. Molar absorptivities (L mol-1 cm-1 ) are ï
> Iron(III) forms a complex with thiocyanate ion that has the formula Fe(SCN) 2+. The complex has an absorption maximum at 580 nm. A specimen of well water was assayed according to the following scheme. Calculate the concentration of iron in parts per mill
> A 5.24-g petroleum specimen was decomposed by wet ashing and subsequently diluted to 500 mL in a volumetric flask. Cobalt was determined by treating 25.00-mL aliquots of this diluted solution as follows: Assume that the Co(II)/ligand chelate obeys Beer&
> What is the “operational definition of pH”? Why is it used?
> The accompanying data (1.00-cm cells) were obtained for the spectrophotometric titration of 10.00 mL of Pd(II) with 2.44 × 10-4 M Nitroso R (O. W. Rollins and M. M. Oldham, Anal. Chem., 1971, 43, 262, DOI: 10.1021/ac60297a026): Calculate th
> Ethylenediaminetetraacetic acid displaces bismuth(III) from its thiourea complex: Bi(tu)63+ + H2Y2- → BiY- + 6tu + 2H+ where tu is the thiourea molecule, (NH2)2CS. Predict the shape of a photometric titration curve based on this process, given that the
> Iron(III) reacts with thiocyanate ion (SCN) to form the red complex, Fe(SCN)2+. Sketch a photometric titration curve for Fe(III) with thiocyanate ion when a photometer with a green filter is used to collect data. Why is a green filter used?
> Sketch a photometric titration curve for the titration of Sn2+ with MnO-4. What color radiation should be used for this titration? Explain.
> A portable photometer with a linear response to radiation registered 75.5 µA with a blank solution in the light path. Replacement of the blank with an absorbing solution yielded a response of 23.7 µA. Calculate (a) The percent transmittance of the sampl
> A photometer with a linear response to radiation gave a reading of 690 mV with a blank in the light path and 169 mV when the blank was replaced by an absorbing solution. Calculate a) The transmittance and absorbance of the absorbing solution. b) The ex
> The logarithm of the molar absorptivity of phenol in aqueous solution is 4.297 at 211 nm. Calculate the range of phenol concentrations that can be used if the absorbance is to be greater than 0.150 and less than 1.500 with a 1.25-cm cell.
> The logarithm of the molar absorptivity for acetone in ethanol is 2.75 at 366 nm. Calculate the range of acetone concentrations that can be used if the absorbance is to be greater than 0.100 and less than 2.000 with a 1.50-cm cell.
> The molar absorptivity for aqueous solutions of phenol at 211 nm is 5.28 × 103 L cm-1 mol-1. Calculate the permissible range of phenol concentrations if the transmittance is to be less than 85% and greater than 7% when the measurements are made in 1.00-c
> The molar absorptivity for the complex formed between bismuth (III) and thiourea is 9.32 × 103 L cm-1 mol-1 at 470 nm. Calculate the range of permissible concentrations for the complex if the absorbance is to be no less than 0.10 nor greater than 0.90 wh
> Give several advantages of a potentiometric titration over a direct potentiometric measurement.
> Define the term spectral bandpass of a monochromator.
> Describe the differences between the following pairs of terms, and list any particular advantages possessed by one over the other: (a) Solid-state photodiodes and phototubes as detectors for electromagnetic radiation. (b) Phototubes and photomultiplier
> The following data were taken from a diode-array spectrophotometer in an experiment to measure the spectrum of the Co (II)-EDTA complex. The column labeled Psolution is the relative signal obtained with sample solution in the cell after subtraction of th
> An interference filter is to be constructed for isolation of the CS2 absorption band at 4.54 µm. a) If the determination is to be based on first-order interference, how thick should the dielectric layer be (refractive index 1.54)? b) What other wavelen
> Define (a) Transducer. (b) Photocurrent. (c) N-type semiconductor. (d) Majority carrier. (e) Depletion layer. (f) Dynodes in a photomultiplier tube.
> What is the difference between an absorption filter and an interference filter?
