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engineering
chemical engineering

Questions and Answers of Chemical Engineering

Determine the number of ions undergoing electron transfer at the surface of an electrode during each second that an electrochemical cell is operated at 0.0175 A at 100% current efficiency and the
Calculate the theoretical potential at 25°C needed to initiate the deposition of
Calculate the initial potential needed for a current of 0.065 A in the cell Co|Co2+ (5.90 ( 10-3 M) ||Zn2+ (2.95 3 10-3 M) |Zn if this cell has a resistance of 4.50 V.
Copper is to be deposited from a solution that is 0.250 M in Cu(II) and is buffered to a pH of 4.00. Oxygen is evolved from the anode at a partial pressure of 730 torr. The cell has a resistance of
A solution is 0.200 M in Co2+ and 0.0650 M in Cd2+. Calculate (a) The Co2+ concentration in the solution as the first cadmium starts to deposit. (b) The cathode potential needed to lower the Co2+
Briefly define (a) Ohmic potential. (b) Controlled-potential electrolysis. (c) Current efficiency.
Electrogravimetric analysis with control of the cathode potential is proposed as a means for separating Bi3+ and Sn2+ in a solution that is 0.250 M in each ion and buffered to pH 1.95. (a) Calculate
A solution is 0.200 M in each of two reducible cations, A and B. Removal of the more reducible species (A) is deemed complete when [A] has been decreased to 1.00 ( 10-5 M. What minimum difference in
Calculate the time needed for a constant current of 0.8510 A to deposit 0.250 g of Co(II) as (a) Elemental cobalt on the surface of a cathode. (b) Co3O4 on an anode. Assume 100% current efficiency
A 0.1330-g sample of a purified organic acid was neutralized by the hydroxide ion produced in 5 min and 24 s by a constant current of 300 mA. Calculate the equivalent mass of the acid in grams.
An excess of HgNH3Y2- was introduced to 25.00 mL of well water. Express the hardness of the water in terms of ppm CaCO3 if the EDTA needed for the titration was generated at a mercury cathode
The nitrobenzene in 300 mg of an organic mixture was reduced to phenylhydroxylamine at a constant potential of 20.96 V (versus SCE) applied to a mercury cathode: C6H5NO2 + 4H+ + 4e¯ ( C6H5NHOH +
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
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
Describe conditions that favor kinetic polarization in an electrochemical cell.
How do electrogravimetric and coulometric methods differ from potentiometric methods? Consider currents, voltages, and instrumentation in your answer.
Distinguish between (a) Voltammetry and amperometry. (b) differential-pulse voltammetry and square-wave voltammetry. (c) A limiting current and a diffusion current. (d) The standard electrode
It has been suggested that many polarograms can be obtained on a solution without depleting the electroactive analyte. Suppose that in a polarographic experiment we monitor the limiting current for
An unknown cadmium(II) solution was analyzed polarographically by the method of standard additions. A 25.00-mL sample of the unknown solution produced a diffusion current of 1.86 (A. Following
Why is a high supporting electrolyte concentration used in most electroanalytical procedures?
In a solution of pH 5.3, the indicator bromocresol purple exhibits a yellow color, but when the pH is 6.0, the indicator solution changes to purple. Discuss why these colors are observed in terms of
Calculate the wavelength of the sodium line at 589 nm in an aqueous solution with a refractive index of 1.35.
What are the units for absorptivity when the path length is given in centimeters and the concentration is expressed in (a) Parts per million? (b) Micrograms per liter? (c) Mass-volume percent? (d)
Express the following absorbances in terms of percent transmittance (a) 0.0356 (b) 0.895 (c) 0.379
Convert the accompanying transmittance data to absorbances. (a) 27.2% (b) 0.579 (c) 30.6% (d) 3.98% (e) 0.093 (f) 63.7%
Describe the differences between "real" deviations from Beer's law and those due to instrumental or chemical factors.
How does an electronic transition resemble a vibrational transition? How do they differ?
(a) An X-ray beam with a wavelength of 2.65 Å. (b) An emission line for copper at 211.0 nm.
Calculate the wavelength in centimeters of (a) An airport tower transmitting at 118.6 MHz. (b) A VOR (radio navigation aid) transmitting at 114.10 kHz. (c) An NMR signal at 105 MHz. (d) An infrared
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
What minimum requirement is needed to obtain reproducible results with a single-beam spectrophotometer?
What is the purpose of (a) the 0% T adjustment and (b) the 100% T adjustment of a spectrophotometer?
What experimental variables must be controlled to assure reproducible absorbance data?
What are the major advantages of Fourier transform IR instruments over dispersive IR instruments?
Define the term effective bandwidth of a monochromator.
Why do quantitative and qualitative analyses often require different monochromator slit widths?
Why are photomultiplier tubes unsuited for the detection of infrared radiation?
Why is iodine sometimes introduced into a tungsten lamp?
Describe the differences between the following pairs of terms and list any particular advantages of one over the other: (a) Spectrophotometers and photometers. (b) Spectrographs and polychromators.
The Wien displacement law states that the wavelength maximum in micrometers for blackbody radiation is (max T = 2.90 ( 103 where T is the temperature in kelvins. Calculate the wavelength maximum for
Stefan's law states that the total energy emitted by a blackbody per unit time and per unit area is Et = (T4 where a is 5.69 3 10-8 W/m2K4. Calculate the total energy output in W/m2 for the
The relationships described in Problems 25-7 and 25-8 may be of help in solving the following. (a) Calculate the wavelength of maximum emission of a tungsten-filament bulb operated at 2870 K and at
Describe the differences between the following pairs of terms and list any particular advantages of one over the other: (a) Spectrophotometers and photometers. (b) Conventional and diode-array
A portable photometer with a linear response to radiation registered 75.5 (A with a blank solution in the light path. Replacement of the blank with an absorbing solution yielded a response of 23.7
Sketch a photometric titration curve for the titration of Sn2+ with MnO4¯. What color radiation should be used for this titration? Explain.
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
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
The accompanying data (1.00-cm cells) were obtained for the spectrophotometric titration of 10.00 mL of Pd(II) with M Nitroso R (O. W. Rollins and M. M. Oldham, Anal. Chem., 1971, 43, 262, DOI:
A 4.97-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
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 scheme below.
A. J. Mukhedkar and N. V. Deshpande (Anal. Chem., 1963, 35, 47, DOI: 10 . 1021 /ac 60 194a014) report on a simultaneous determination for cobalt and nickel based on absorption by their 8-quinolinol
What experimental variables must be controlled to assure reproducible absorbance data? Discuss.
What is (are) advantage(s) of the multiple standard addition method over the single-point standard addition method?
The molar absorptivity for the complex formed between bismuth (III) and thiourea is 9.32 ( 103 L cm21 mol-1 at 470 nm. Calculate the range of permissible concentrations for the complex if the
The molar absorptivity for aqueous solutions of phenol at 211 nm is 6.17 ( 103 L cm-1 mol-1. Calculate the permissible range of phenol concentrations if the transmittance is to be less than 85% and
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
The logarithm of the molar absorptivity of phenol in aqueous solution is 3.812 at 211 nm. Calculate the range of phenol concentrations that can be used if the absorbance is to be greater than 0.150
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
Briefly describe or define (a) Fluorescence. (b) Internal conversion. (c) Stokes shift. (d) Inner-filter effect.
Why do some absorbing compounds fluoresce while others do not?
Describe the characteristics of organic compounds that fluoresce.
Explain why molecular fluorescence often occurs at a longer wavelength than the exciting radiation.
Describe the components of a filter fluorometer and a spectrofluorometer.
Describe the basic differences among atomic emission, atomic absorption, and atomic fluorescence spectroscopy.
Define (a) Atomization. (b) Doppler broadening. (c) Plasma. (d) Hollow-cathode lamp. (e) Additive interference. (f) Chemical interference. (g) Protective agent.
Why is atomic emission more sensitive to flame instability than atomic absorption?
Why are ionization interferences usually not as severe in the ICP as they are in flames?
Why are higher resolution monochromators found in ICP atomic emission spectrometers than in flame atomic absorption spectrometers?
Name four characteristics of inductively coupled plasmas that make them suitable for atomic emission spectrometry.
Define (a) Dalton. (b) mass number. (c) time-of-flight analyzer.
What function does the ICP torch serve in mass spectrometry?
What are the ordinate and the abscissa of an ordinary mass spectrum?
What types of interferences are encountered in ICPMS?
What is the purpose of an internal standard in ICPMS?
Define the following terms as they are used in kinetic methods of analysis. (a) Order of a reaction (b) Enzyme (c) Michaelis constant (d) Integral method
Find the relative error associated with the assumption that k' is invariant during the course of a pseudo-first-order reaction under the following conditions:
Equation 30-19 can be rearranged to produce the EquationWhere vmax 5 k2[E]0, the maximum velocity when [S] is large. (a) Suggest a way to use this equation in the construction of a calibration
Copper (II) forms a 1:1 complex with the organic complexing agent R in acidic medium. The formation of the complex can be monitored by spectrophotometer at 480 nm. Use the following data collected
The enzyme monoamine oxidase catalyzes the oxidation of amines to aldehydes. For tryptamine, Km for the enzyme is 4.0 x 10-4 M, and vmax = k2[E]0 = 1.6 x 10-3 mM/min at pH 8. Find the concentration
Calculate the product concentrations versus time for a pseudo-first-order reaction with k9 5 0.015 s-1 and [A]0 5 0.005 M. Use times of 0.000 s, 0.001 s, 0.01 s, 0.1 s, 0.2 s 0.5 s, 1.0 s, 2.0 s, 5.0
List three advantages of kinetic methods. Can you think of two possible limitations of kinetic methods when compared to equilibrium methods?
Derive an expression for the half-life of the reactant in a first-order process in terms of the rate constant k.
Find the natural lifetime in seconds for first-order reactions corresponding to (a) k = 0.497 s-1. (b) [A]0 = 3.16 M, and [A]t 5 0.496 M at t 5 3876 s. (c) half-life, t1/2, 5 26.5 years.
Find the first-order rate constant for a reaction that is 75.0% complete in (a) 0.0100 s. (b) 1.00 s. (c) 26.8 ms.
Find the number of half-lives required to reach the following levels of completion: (a) 10%. (b) 90%. (c) 99.9%.
The distribution constant for X between n-hexane and water is 8.9. Calculate the concentration of X remaining in the aqueous phase after 50.0 mL of 0.200 M X is treated by extraction with the
What volume of n-hexane is required to decrease the concentration of X in Problem 31-11 to 1.00 x 10-4 M if 25.0 mL of 0.0500 M X is extracted with (a) 25.0-mL portions? (b) 10.0-mL portions? (c)
What is the minimum distribution coefficient that permits removal of 99% of a solute from 50.0 mL of water with (a) Two 25.0-mL extractions with toluene? (b) Five 10.0-mL extractions with toluene?
A 0.150 M aqueous solution of the weak organic acid HA was prepared from the pure compound, and three 50.0-mL aliquots were transferred to 100.0-mL volumetric flasks. Solution 1 was diluted to 100.0
The total cation content of natural water is often determined by exchanging the cations for hydrogen ions on a strong-acid ion-exchange resin. A 25.0-mL sample of a natural water was diluted to 100
An aqueous solution containing MgCl2 and HCl was analyzed by first titrating a 25.00-mL aliquot to a bromocresol green end point with 17.53 mL of 0.02932 M NaOH. A 10.00-mL aliquot was then diluted
A packed column in gas chromatography had an inside diameter of 5.0 mm. The measured volumetric flow rate at the column outlet was 48.0 mL/min. If the column porosity was 0.43, what was the linear
From the data in Problem 31-24, calculate for A, B, C, and DIn problem 31-24A chromatogram of a mixture of species A. B, C, and D provided the following data:(a) The retention factor. (b) The
Define (a) Elution. (b) Stationary phase. (c) Retention time. (d) Selectivity factor.
List the variables that lead to band broadening in chromatography.
How do gas-liquid and gas-solid chromatography differ?
What are the principal advantages and the principal limitations of each of the detectors listed in Problem 32-10?In Problem 32-10Describe the principle on which each of the followingGC detectors are
What are megabore open tubular columns? Why are they used?
Why are gas chromatographic stationary phases often bonded and cross-linked? What do these terms mean?
List the variables that lead to (a) Band broadening (b) Band separation in gas-liquid chromatography.

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