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chemical engineering

Questions and Answers of Chemical Engineering

The wavelengths of maximum absorption and emission of anthracene in Figure 17-22 are approximately 357 and 402 nm. Molar absorptivities at these wavelengths are εex 9.0 × 103M-1 cm-1 and εem = 5
Calculate the frequency (Hz), wavenumber (cm-1), and energy (J/photon and J/[mol of photons]) of visible light with a wavelength of 562 nm.
Selenium from 0.108 g of Brazil nuts was converted into the fluorescent product in Reaction 17-15, which was extracted into 10.0 mL of cyclohexane. Then 2.00 mL of the cyclohexane solution were
Which molecular processes correspond to the energies of microwave, infrared, visible, and ultraviolet photons?
Characteristic orange light produced by sodium in a flame is due to an intense emission called the sodium D line, which is actually a doublet, with wavelengths (measured in vacuum) of 589.157 88 and
Color and absorption spectra. Color Plate 15 shows colored solutions and their spectra. From Table 17-1, predict the color of each solution from the wavelength of maximum absorption. Do observed
This problem can be worked by calculator or with the spreadsheet in Figure 18-5. Consider compounds X and Y in the example labeled "Analysis of a Mixture, Using Equations 18-6" in Section 18-1. Find
Figure 18-7 is a Scatchard plot for the addition of 0-20 nM antigen X to a fixed concentration of antibody P (P0 = 10 nM). Prepare a Scatchard plot from the data in the table and find K for the
Data in the table come from a student experiment to measure the binding constant of the radioactively labeled hormone estradiol (X) to the protein, bovine serum albumin (P). Estradiol (7.5 nM) was
Iodine reacts with mesitylene to form a complex with an absorption maximum at 332 nm in CCl4 solution:(a) Given that the product absorbs at 332 nm, but neither reactant has significant absorbance at
Now we use Solver to find K for the previous problem. The only absorbing species at 332 nm is the complex, so, from Beer's law, [complex] = A/Îµ (because pathlength = 1.000 cm). I2 is either free
Method of continuous variation. Make a graph of absorbance versus mole fraction of thiocyanate from the data in the table.(a) What is the stoichiometry of the predominant Fe(SCN)n3-n species?(b) Why
The indicator xylenol orange (Table 11-3) forms a complex with Zr(IV) in HCl solution. Prepare a Job plot from the data in the table and suggest the stoichiometry of the complex (xylenol
Simulating a Job's plot. Consider the reaction , for which K [AB2]/[A][B]2. Suppose that the following mixtures of A and B at a fixed total concentration of 104M are prepared:(a) Prepare a
A study was conducted with derivatives of the DNA nucleotide bases adenine and thymine bound inside micelles (Box 25-1) in aqueous solution.Sodium dodecyl sulfate forms micelles with the hydrocarbon
Explain what is done in flow injection analysis and sequential injection. What is the principal difference between the two techniques? Which one is called "lab-on-a-valve"?
Explain how signal amplification is achieved in enzymelinked immunosorbent assays.
The figure shows spectra of 1.00×10-4 M MnO-4, 1.00×10-4 M Cr2O72-, and an unknown mixture of both, all in 1.000-cm-pathlength cells. Absorbances are given in the table. Use the least-squares
What is the advantage of a time-resolved emission measurement with Eu3+ versus measurement of fluorescence from organic chromophores?
Here is an immunoassay to measure explosives such as trinitrotoluene (TNT) in organic solvent extracts of soil. The assay employs a flow cytometer, which counts small particles (such as living cells)
The graph shows the effect of pH on quenching of luminescence of tris(2,2 bipyridine)Ru(II) by 2,6-dimethylphenol. The ordinate, KSV, is the collection of constants, kq/(ke + kd), in the Stern-Volmer
Consider an aqueous solution with a high concentration of micelles (Box 25-1) and relatively low concentrations of the fluorescent molecule pyrene and a quencher (cetylpyridinium chloride, designated
When are isosbestic points observed and why?
The metal ion indicator xylenol orange (Table 11-3) is yellow at pH 6 (λmax = 439 nm). The spectral changes that occur as VO2+ is added to the indicator at pH 6 are shown here. The mole ratio
Infrared spectra are customarily recorded on a transmittance scale so that weak and strong bands can be displayed on the same scale. The region near 2 000 cm-1 in the infrared spectra of compounds A
Spectroscopic data for the indicators thymol blue (TB), semithymol blue (STB), and methylthymol blue (MTB) are shown in the table. A solution of TB, STB, and MTB in a 1.000-cm cuvet had absorbances
The spreadsheet gives the product b for four pure compounds and a mixture at infrared wavelengths. Modify Figure 18-5 to solve four equations and find the concentration of each compound. You can
A solution was prepared by mixing 25.00 mL of 0.080 0 M aniline, 25.00 mL of 0.060 0 M sulfanilic acid, and 1.00 mL of 1.23 × 10-4 M HIn and then diluting to 100.0 mL. (HIn stands for protonated
Chemical equilibrium and analysis of a mixture. (Warning! This is a long problem.) A remote optical sensor for CO2 in the ocean was designed to operate without the need for calibration.The sensor
Describe the role of each component of the spectrophotometer in Figure 19-1.
Show that a grating with 103 grooves/cm provides a dispersion of 5.8° per μm of wavelength if n = 1 and ɸ = 10° in Equation 19-4.
(a) What resolution is required for a diffraction grating to resolve wavelengths of 512.23 and 512.26 nm? (b) With a resolution of 104, how close in nm is the closest line to 512.23 nm that can
(a) The true absorbance of a sample is 1.500, but 0.50% stray light reaches the detector. Find the apparent transmittance and apparent absorbance of the sample. (b) How much stray light can be
Calculate the power per unit area (the exitance, W/m2) radiating from a blackbody at 77 K (liquid nitrogen temperature) and at 298 K (room temperature).
The exitance (power per unit area per unit wavelength) from a blackbody (Box 19-1) is given by the Planck distribution:where _ is wavelength, T is temperature (K), h is Planck's constant, c is the
In the cavity ring-down measurement at the opening of this chapter, absorbance is given bywhere L is the length of the cavity between mirrors, c is the speed of light,t is the ring down lifetime with
Light passes from benzene (medium 1) to water (medium 2) in Figure 19-19 at (a) θ1 = 30° or (b) θ1= 0°. Find the angle 2 in each case.
Explain how an optical fiber works. Why does the fiber still work when it is bent?
The photograph of upconversion in Color Plate 19 shows total internal reflection of the blue ray inside the cuvet. The angle of incidence of the blue ray on the wall of the cuvet is ≈ 55θ. We
Explain how a laser generates light. List important properties of laser light.
Explain how the attenuated total reflection sensor in Figure 19-23 works.
Consider a planar waveguide used for attenuated total reflection measurement of a film coated on one surface of the waveguide. For a given angle of incidence, the sensitivity of attenuated total
(a) Find the critical value of i in Figure 19-20 beyond which there is total internal reflection in a ZrF4-based infrared optical fiber whose core refractive index is 1.52 and whose cladding
Find the minimum angle i for total reflection in the optical fiber in Figure 19-20 if the index of refraction of the cladding is 1.400 and the index of refraction of the core is (a) 1.600 or (b)
The prism shown here is used to totally reflect light at a 90 angle. No surface of this prism is silvered. Use Snell's law to explain why total reflection occurs. What is the minimum refractive index
Here is an extremely sensitive method for measuring nitrite (NO2-) down to 1 nM in natural waters. The water sample is treated with sulfanilamide and N-(1 naphthylethylenediamine) in acidsolution to
(a) A particular silica glass waveguide is reported to have a loss coefficient of 0.050 dB/cm (power out/power in, defined in Problem 19-22) for 514-nm-wavelength light. The thickness of the
The variation of refractive index, n, with wavelength for fused silica is given bywhere is expressed in Î¼m. (a) Make a graph of n versus Î» with points at the following
The interferometer mirror of a Fourier transform infrared spectrophotometer travels 1 cm. (a) How many centimeters is the maximum retardation, ∆?
Describe three general types of noise that have a different dependence on frequency. Give an example of the source of each kind of noise.
Explain how beam chopping reduces line noise and noise from source drift.
Explain how the difference voltage in Figure 19-35 reduces noise from source flicker.
A measurement with a signal-to-noise ratio of 100/1 can be thought of as a signal, S, with 1% uncertainty, e. That is, the measurement is S ± e = 100 ± 1. (a) Use the rules for propagation of
Results of an electrochemical experiment are shown in the figure. In each case, a voltage is applied between two electrodes at time = 20 s and the absorbance of a solution decreases until the voltage
Which variables increase the resolution of a grating? Which variables increase the dispersion of the grating? How is the blaze angle chosen to optimize a grating for a particular wavelength?
Explain how the following detectors of visible radiation work: (a) photomultiplier tube, (b) photodiode array, and (c) charge coupled device.
Deuterated triglycine sulfate (abbreviated DTGS) is a common ferroelectric infrared detector material. Explain how it works.
Consider a reflection grating operating with an incident angle of 40 in Figure 19-7.(a) How many lines per centimeter should be etched in the grating if the first-order diffraction angle for 600-nm
In which technique, atomic absorption or atomic emission, is flame temperature stability more critical? Why?
What is the purpose of a matrix-matched standard in laserinduced breakdown spectroscopy?
Laser atomic fluorescence excitation and emission spectra of sodium in an air-acetylene flame are shown here. In the excitation spectrum, the laser (bandwidth 0.03 nm) was scanned through various
Concentrations (pg per g of snow) of metals by atomic fluorescence in the Agassiz Ice Cap in Greenland for the period 1988-1992 are 31 Pb, 1.04 (± 0.17) × 102; Tl, 0.43 0.087; Cd, 3.5 ± 0.87;
Calculate the emission wavelength (nm) of excited atoms that lie 3.371 × 10-19 J per molecule above the ground state.
Derive the entries for 500 nm in Table 20-3. Find N*/N0 at 6 000 K if g* = 3 and g0 = 1?
Calculate the Doppler linewidth for the 589-nm line of Na and for the 254-nm line of Hg, both at 2 000 K.
The first excited state of Ca is reached by absorption of 422.7-nm light. (a) Find the energy difference (kJ/mol) between ground and excited states. (b) The degeneracies are g*/g0 = 3 for Ca. Find
An electron volt (eV) is the energy change of an electron moved through a potential difference of 1 volt: eV (1.602 Ã— 10-19C)(1 V) 1.602 Ã— 10-19 J per electron 96.49 KJ
MgO prevents premature evaporation of Al in a furnace by maintaining the aluminum as Al2O3. Another type of matrix modifier prevents loss of signal from the atom X that readily forms the molecular
The 20-μm-radius laser ablation pit in Figure 20-28 was created by a laser pulse with a duration of 10 ns and an energy of 2.4 mJ. Express the laser power density in units of W/cm2. Recall that 1 W
To measure Ca in breakfast cereal, 0.521 6 g of crushed Cheerios was ashed in a crucible at 600ºC in air for 2 h.32 The residue was dissolved in 6 M HCl, quantitatively transferred to a
A solution was prepared by mixing 10.00 mL of unknown (X) with 5.00 mL of standard (S) containing 8.24 g S/mL and diluting the mixture to 50.0 mL. The measured signal quotient was (signal due to
Potassium standards gave the following emission intensities at 404.3 nm. Emission from the unknown was 417. Find [K+] and its uncertainty in the unknown.
Tin is leached (dissolved) into canned foods from the tin-plated steel can.33 For analysis by inductively coupled plasma-atomic emission, food is digested by microwave heating in a Teflon bomb
Titanocene dichloride, (-C5H5)2TiCl2, is a potential antitumor drug thought to be carried to cancer cells by the protein transferring (Figure 17-7). To measure the Ti(IV) binding capacity of
Figure 20-10 shows a temperature profile for a furnace atomic absorption experiment. Explain the purpose of each different part of the heating profile.
State the advantages and disadvantages of the inductively coupled plasma compared with a flame in atomic spectroscopy.
Explain what is meant by the Doppler effect. Rationalize why Doppler broadening increases with increasing temperature and decreasing mass in Equation 20-5.
Explain how the following background correction techniques work: (a) beam chopping; (b) deuterium lamp; (c) Zeeman.
Explain what is meant by spectral, chemical, ionization, and isobaric interference.
(a) Explain the purpose of the collision cell in Figure 20-30.(b) Explain the purpose of a dynamic reaction cell, which can replace the collision cell.(c) In geologic strontium isotopic analysis,
Briefly describe how a magnetic sector mass spectrometer works.
Referring to Exercise 21-C, predict the relative amounts of C2H2 79Br2, C2H2 79Br81Br, and C2H2 81Br2 in 1,2-dibromoethylene. Compare your answer with Figure 21-7.Figure 21-7
Referring to Exercise 21-C, predict the relative abundances of 10B2H6, 10B11BH6, and 11B2H6 for diborane (B2H6).
Find the number of rings plus double bonds in molecules with the following compositions and draw one plausible structure for each: (a) C11H18N2O3; (b) C12H15BrNPOS; (c) Fragment in a
(Each part of this problem is quite long and best worked by groups of students.) Peak intensities of the molecular ion region are listed in parts (a) - (g) and shown in the figure. Identify which
Suggest a composition for the halogen compound whose mass spectrum is shown in the figure. Assign each of the major peaks.
Box 21-3 (page 509) shows that CO2 in human breath in the United States has a value of δ13C different from that of CO2 in human breath in mainland Europe. Suggest an explanation.
(a) The mass of 1H in Table 21-1 is 1.007 825 Da. Compare it with the sum of the masses of a proton and an electron given in the table.(b) 2H (deuterium) contains one proton, one neutron, and one
From the natural abundance of 79Br and 81Br, predict the relative amounts of CH79Br3, CH79Br2 81Br, CH79Br81Br2, and CH81Br3. As in Exercise 21-C, the fraction of each isotopic molecule comes
This problem could lead to serious brain injury.) For an element with three isotopes with abundances a, b, and c, the distribution of isotopes in a molecule with n atoms is based on the expansion of
Explain how a double-focusing mass spectrometer achieves high resolution.
How are ions created for each of the mass spectra in Figure 21-4? Why are the two spectra so different?Figure 21-4
A limitation on how many spectra per second can be recorded by a time-of-flight mass spectrometer is the time it takes the slowest ions to go from the source to the detector. Suppose we want to scan
What is the purpose of the reflectron in a time-of-flight mass spectrometer?
(a) The mean free path is the average distance a molecule travels before colliding with another molecule. The mean free path,λ, is given λ = KTI (√2σP) by where k is Boltzmann's constant, T is
What is collisionally activated dissociation? At what points in a mass spectrometer does it occur?
What is the difference between a reconstructed total ion chromatogram, an extracted ion chromatogram, and a selected ion chromatogram?
What is selected reaction monitoring? Why is it also called MS/MS? Why does it improve the signal/noise ratio for a particular analyte?
(a) To detect the drug ibuprofen by liquid chromatography/ mass spectrometry, would you choose the positive or negative ion mode for the spectrometer? Would you choose acidic or neutral
An electrospray/transmission quadrupole mass spectrum of the α-chain of hemoglobin from acidic solution exhibits nine peaks corresponding to Mn+n. Find the charge, n, for peaks A-I. Calculate the

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