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chemical engineering

Questions and Answers of Chemical Engineering

The "rule of three" states that the retention factor for a given solute decreases approximately threefold when the organic phase increases by 10%. In Figure 24-12, tm = 2.7 min. Find k for peak 5 at
(a) Make a graph showing retention times of peaks 6, 7, and 8 in Figure 24-12 as a function of %acetonitrile (%B). Predict the retention time of peak 8 at 45% B. (b) In Figure 24-12, tm = 2.7 min.
(a) Make a graph showing the retention time of each peak in Figure 24-25 in chromatograms B, F, and C as a function of position along the line BC. Predict the retention times for solvent compositions
Suppose that in Figure 24-25 the optimum concentrations of solvents at points A, B, and C are 50% acetonitrile, 60% methanol, and 40% tetrahydrofuran, respectively. What will be the solvent
(a) When you try separating an unknown mixture by reversedphase chromatography with 50% acetonitrile/50% water, the peaks are too close together and are eluted in the range k = 2-6. Should you use a
A mixture of 14 compounds was subjected to a reversedphase gradient separation going from 5% to 100% acetonitrile with a gradient time of 60 min. The sample was injected at t = dwell time. All peaks
(a) List ways in which the resolution between two closely spaced peaks might be changed.(b) After optimization of an isocratic elution with several solvents, the resolution of two peaks is 1.2. How
(a) Why is high pressure needed in HPLC? (b) What is a bonded phase in liquid chromatography?
(a) You wish to use a wide gradient from 5 vol% to 95 vol% B for the first separation of a mixture of small molecules to decide whether to use gradient or isocratic elution. What should be the
(a) Use Equation 24-1 to estimate the length of column required to achieve 1.0 × 104 plates if the stationary phase particle size is 10.0, 5.0, 3.0, or 1.5 μm.
If a 15-cm-long column has a plate height of 5.0 μm, what will be the half-width (in seconds) of a peak eluted at 10.0 min? If plate height = 25 μm, what will be w1/2?
Why are silica stationary phases generally limited to operating in the pH range 2-8? Why does the silica in Figure 24-8 have improved stability at low pH?
HPLC peaks should generally not have an asymmetry factor A/B in Figure 22-14 outside the range 0.9 - 1.5.(a) Sketch the shape of a peak with an asymmetry of 1.8.(b) What might you do to correct the
State the purpose of the separator and suppressor in suppressedion chromatography. For cation chromatography, why is the suppressor an anion-exchange membrane?
(a) Explain how anions and cations can be separated by hydrophilic interaction chromatography in Figure 25-5, using the zwitterionic stationary phase in Figure 24-14. Why does the gradient go from
In the separation of proteins by hydrophobic interaction chromatograpy, why does eluent strength increase with decreasing salt concentration in the aqueous eluent?
In ion-exclusion chromatography, ions are separated from nonelectrolytes by an ion exchange column. Nonelectrolytes penetrate the stationary phase, whereas half of the ions are repelled by the fixed
(a) Norepinephrine (NE) in human urine can be assayed by ion-pair chromatography by using an octadecylsilane stationary phase and sodium octyl sulfate as the mobile-phase additive. Electrochemical
Decomposition of dithionite (S2O2-4) was studied by chromatography on an anion exchange column eluted with 20 mM trisodium 1,3,6-naphthalenetrisulfonate in 90 vol% H2O/10 vol% CH3CN with ultraviolet
(a) Suppose that the reservoir in Figure 25-8 contains 1.5 L of 2.0 M K2PO4. For how many hours can the reservoir provide 20 mM KOH at a flow rate of 1.0 mL/min if 75% consumption of K+ in the
The system in Figure 25-8 can be adapted to produce the strong acid eluent methanesulfonic acid (CH3SO-3H+). For this purpose, the polarity of the electrodes is reversed and the reservoir can contain
(a) How can molecular exclusion chromatography be used to measure the molecular mass of a protein?(b) Which pore size in Figure 25-17 is most suitable for chromatography of molecules with molecular
A gel-filtration column has a radius, r, of 0.80 cm and a length, l, of 20.0 cm. (a) Calculate the volume, Vt, of the column, which is equal to πr2l. (b) The void volume, Vo, was 18.1 mL, and the
Ferritin (molecular mass 450 000), transferrin (molecular mass 80 000), and ferric citrate were separated by molecular exclusion chromatography on Bio-Gel P-300. The column had a length of 37 cm and
(a) The void volume in Figure 25-17 is the volume at which the curves rise vertically at the left. What is the smallest molecular mass of molecules excluded from the 10-nm-pore-size column?(b) What
A polystyrene resin molecular exclusion HPLC column has a diameter of 7.8 mm and a length of 30 cm. The solid portions of the gel particles occupy 20% of the volume, the pores occupy 40%, and the
The following substances were separated on a gel filtration column. Estimate the molecular mass of the unknown.
What is electroosmosis?
Electroosmotic velocities of buffered solutions are shown for a bare silica capillary and one with aminopropyl groups (silica - Si - CH2CH2CH2NH2) covalently attached to the wall. A positive sign
Fluorescent derivatives of amino acids separated by capillary zone electrophoresis had migration times with the following order: arginine (fastest)
What is the principal source of zone broadening in ideal capillary electrophoresis?
Consider the electrophoresis of heparin in Figure 25-21.(a) Electrophoresis was carried out at pH 2.8, at which sulfate groups are negative. Why was reverse polarity (detector end positive) used?(b)
(a) An electrophoresis channel etched into a glass plate has a rectangular 12 × 50 μm cross section. How long (mm) is the sample zone for a 100-pL sample?(b) If sample travels 24 mm in 8 s to reach
State three different methods to reduce electroosmotic flow. Why does the direction of electroosmotic flow change when a silica capillary is washed with a cationic surfactant?
What is deionized water? What kind of impurities are not removed by deionization?
Explain how neutral molecules can be separated by micellar electrokinetic chromatography. Why is this a form of chromatography?
(a) What pressure difference is required to inject a sample equal to 1.0% of the length of a 60.0-cm capillary in 4.0 s if the diameter is 50 μm? Assume that the viscosity of the solution is 0.001 0
(a) How many moles of analyte are present in a 10.0 - μM solution that occupies 1.0% of the length of a 25- μm 60.0-cm capillary? (b) What voltage is required to inject this many moles into a
Measure the number of plates for the electrophoretic peak in Figure 25-23. Use Equation 22-29 for asymmetric peaks to find the number of plates for the chromatographic peak.
(a) A long thin molecule has a greater friction coefficient than a short fat molecule. Predict whether fumarate or maleate will have greater electrophoretic mobility.(b) Electrophoresis is run with
(a) A particular solution in a particular capillary has an electroosmotic mobility of 1.3 × 10-8 m2/(V s) at pH2 and 8.1 × 10-8 m2/(V s) at pH 12. How long will it take a neutral solute to travel
The effect on resolution of increasing voltage from 28 to 120 kV. (a) What is the expected ratio of migration times (t120 kV/t28 kV) in the two experiments? Measure the migration times for peak 1 and
The observed behavior of benzyl alcohol (C6H5CH2OH) in capillary electrophoresis is given here. Draw a graph showing the number of plates versus the electric field and explain what happens as the
Measure the width of the 35Cl- peak at half-height in Figure 25-36 and calculate the plate number. The capillary was 40.0 cm in length. Find the plate height.
The migration time for Cl- in a capillary zone electrophoresis experiment is 17.12 min and the migration time for I- is 17.78 min. From mobilities in Table 14 - 1, predict the migration time of Br-.
The exchange capacity of an ion-exchange resin can be defined as the number of moles of charged sites per gram of dry resin. Describe how you would measure the exchange capacity of an anionexchange
Ferritin is a hollow iron-storage protein61 consisting of 24 subunits that are a variable mixture of heavy (H) or light (L) chains, arranged in octahedral symmetry. The hollow center, with a diameter
Electrophoretic mobility is proportional to charge. If members of a charge ladder (Figure 25-26) have the same friction coefficient (that is, the same size and shape), then the charge of the
Resolution. Suppose that the electroosmotic mobility of a solution is + 1.61 × 10-7 m2/(V ∙ s). How many plates are required to separate sulfate from bromide with a resolution of 2.0? Use Table
The water-soluble vitamins niacinamide (a neutral compound), riboflavin (a neutral compound), niacin (an anion), and thiamine (a cation) were separated by micellar electrokinetic chromatography in 15
When the following three compounds are separated by micellar electrokinetic chromatography at pH 9.6, three peaks are observed. When 10 mM Î± - cyclodextrin is added to the run buffer,
A van Deemter plot for the separation of neutral dyes by micellar electrokinetic chromatography is shown below.62(a) Explain why plate height increases at low and high velocities.(b) The irregular
To obtain the best separation of two weak acids in capillary electrophoresis, it makes sense to use the pH at which their charge difference is greatest. Prepare a spreadsheet to examine the charges
Optimizing a separation of acids. Benzoic acid containing 16O can be separated from benzoic acid containing 18O by electrophoresis at a suitable pH because they have slightly different acid
(a) Describe how ion mobility spectrometry works and state the analogies between this technique and capillary electrophoresis.(b) As in electrophoresis, the velocity, u, of a gas-phase ion is u =
Consider a negatively charged protein adsorbed on an anionexchange gel at pH 8.(a) How will a gradient of eluent pH (from pH 8 to some lower pH) be useful for eluting the protein? Assume that the
Propose a scheme for separating trim ethylamine, dim ethylamine, methylamine, and ammonia from one another by ion-exchange chromatography.
Suppose that an ion-exchange resin (R-Na+) is immersed in a solution of NaCl. Let the concentration of R in the resin be 3.0 M.(a) What will the ratio [Cl-]o/[Cl-]I be if [Cl-]o is 0.10 M?(b) What
Material balance. If you intend to measure all the anions and cations in an unknown, one sanity check on your results is that the total positive charge should equal the total negative charge.
(a) What is the difference between absorption and adsorption?(b) How is an inclusion different from an occlusion?
A 50.00-mL solution containing NaBr was treated with excess AgNO3 to precipitate 0.214 6 g of AgBr (FM 187.772). What was the molarity of NaBr in the solution?
To find the Ce4+ content of a solid, 4.37 g were dissolved and treated with excess iodate to precipitate Ce(IO3)4. The precipitate was collected, washed well, dried, and ignited to produce 0.104 g of
Marie Curie dissolved 0.091 92 g of RaCl2 and treated it with excess AgNO3 to precipitate 0.08890 g of AgCl. In her time (1900), the atomic mass of Ag was known to be 107.8 and that of Cl was 35.4.
A 0.05002-g sample of impure piperazine contained 71.29 wt% piperazine (FM 86.136). How many grams of product (FM 206.240) will be formed when this sample is analyzed by Reaction 26-6?
Name the product obtained in Figure 26-4 when calcium salicylate monohydrate is heated to 550°C and to 1000°C. Using the formula masses of these products, calculate what mass is expected to remain
A method to measure soluble organic carbon in seawater includes oxidation of the organic materials to CO2 with K2S2O8, followed by gravimetric determination of the CO2 trapped by a column of
How many milliliters of 2.15% alcoholic dimethylglyoxime should be used to provide a 50.0% excess for Reaction 26-7 with 0.9984g of steel containing 2.07 wt% Ni? Assume that the density of the
Twenty dietary iron tablets with a total mass of 22.131 g were ground and mixed thoroughly. Then 2.998 g of the powder were dissolved in HNO3 and heated to convert all iron into Fe3+. Addition of NH3
Finely ground mineral (0.632 4 g) was dissolved in 25 mL of boiling 4 M HCl and diluted with 175 mL H2O containing two drops of methyl red indicator. The solution was heated to 100C, and 50 mL of
Man in the vat problem.11 Long ago, a workman at a dye factory fell into a vat containing hot, concentrated sulfuric and nitric acids. He dissolved completely! Because nobody witnessed the accident,
A 1.475-g sample containing NH4Cl(FM 53.492), K2CO3 (FM 138.21), and inert ingredients was dissolved to give 0.100 L of solution. A 25.0-mL aliquot was acidified and treated with excess sodium
A mixture containing only Al2O3 (FM 101.96) and Fe2O3 (FM 159.69) weighs 2.019 g. When heated under a stream of H2, Al2O3 is unchanged, but Fe2O3 is converted into metallic Fe plus H2O(g). If the
A solid mixture weighing 0.5485 g contained only ferrous ammonium sulfate hexahydrate and ferrous chloride hexahydrate. The sample was dissolved in 1M H2SO4, oxidized to Fe3+ with H2O2, and
Propagation of error. A mixture containing only silver nitrate and mercurous nitrate was dissolved in water and treated with excess sodium cobalticyanide, Na3[Co(CN)6] to precipitate both
The thermo gravimetric trace below shows mass loss by Y2(OH)5Cl ˆ™ xH2O upon heating. In the first step, waters of hydration are lost to give 8.1% mass loss. After a second decomposition step,
Thermogravimetric analysis and propagation of error.12 Crystals of deuterated potassium dihydrogen phosphate, K(DxH1 - x)2PO4, are used in optics as a light valve, as a light deflector, and for
When the high-temperature superconductor yttrium barium copper oxide (see Chapter 15 opening and Box 15-3) is heated under flowing H2, the solid remaining at 1 000C is a mixture of Y2O3, BaO, and Cu.
A reprecipitation was employed to remove occluded NO3-from BaSO4 prior to isotopic analysis of oxygen for geologic studies.13 Approximately 30 mg of BaSO4 crystals were mixed with 15 mL of 0.05 M
What is the difference between combustion and pyrolysis?
Why is tin used to encapsulate a sample for combustion analysis?
Why is sample dropped into the preheated furnace before the oxygen concentration reaches its peak in Figure 26-7?
Write a balanced equation for the combustion of benzoic acid, C6H5CO2H, to give CO2 and H2O. How many milligrams of CO2 and of H2O will be produced by the combustion of 4.635 mg of benzoic acid?
Combustion analysis of a compound known to contain just C, H, N, and O demonstrated that it is 46.21 wt% C, 9.02 wt% H, 13.74 wt% N, and, by difference, 100 - 46.21 - 9.02 -13.74 = 31.03% O. This
A mixture weighing 7.290 mg contained only cyclohexane, C6H12(FM 84.159), and oxirane, C2H4O (FM 44.053). When the mixture was analyzed by combustion analysis, 21.999 mg of CO2 (FM 44.010) were
Combustion analysis of an organic compound gave the composition 71.17 ± 0.41 wt% C, 6.76 ± 0.12 wt% H, and 10.34 ± 0.08 wt% N. Find the coefficients h and n and their uncertainties x and y in the
One way to determine sulfur is by combustion analysis. This procedure produces a mixture of SO2 and SO3 that can be passed through H2O2 to convert both into H2SO4, which is titrated with standard
In Experiment 1, 200.0 mL of solution containing 10.0 mg of SO42- (from Na2SO4) were treated with excess BaCl2 solution to precipitate BaSO4 containing some coprecipitated Cl_. To find out how much
What measures can be taken to decrease the relative super saturation during a precipitation?
Describe the chemistry that occurs in each of the following regions in curve (a) in Figure 26-10: (i) before the first equivalence point; (ii) at the first equivalence point; (iii) between the first
Consider the titration of 25.00 mL of 0.08230 M KI with 0.051 10 M AgNO3. Calculate pAg+ at the following volumes of added AgNO3: (a) 39.00 mL; (b) Ve; (c) 44.30 mL.
The text claims that I- precipitation is not complete before Cl- begins to precipitate in Figure 26-10. Calculate [Ag+] at the equivalence point in the titration of I- alone. Show that this
A 25.00-mL solution containing 0.03110 M Na2C2O4 was titrated with 0.02570 M Ca(NO3)2 to precipitate calcium oxalate:.Find pCa2+ at the following volumes of Ca(NO3)2: (a) 10.00; (b) Ve; (c) 35.00 mL.
In precipitation titrations of halides by Ag+, the ion pairAgX(aq) (X = Cl, Br, I) is in equilibrium with the precipitate. Use Appendix J to find the concentrations of AgCl(aq), AgBr(aq), and AgI(aq)
A 0.238 6-g sample contained only NaCl and KBr. It was dissolved in water and required 48.40 mL of 0.048 37 M AgNO3 for complete titration of both halides [giving AgCl(s) and AgBr(s)]. Calculate the
A procedure15 for determining halogens in organic compounds uses an argentometric titration. To 50 mL of anhydrous ether is added a carefully weighed sample (10 - 100 mg) of unknown, plus 2 mL of
Derive an expression analogous to Equation 26-18 for the titration of M+ (concentration C0M, volume = V0M ) with X- (titrant concentration = C0X ). Your equation allows you to compute the volume of
Consider precipitation of Xx- with Mm+:xMm+ + mXx- ‡Œ MxXm Ksp = [Mm+]x[Xx-]mWrite mass balance equations for M and X and derive the equationwhere [Xx-] = (Ksp/[Mm+]x)1/m.
Use the equation in the Problem 26-49 to calculate the titration curve for 10.0 mL of 0.100 M CrO42- titrated with 0.100 M Ag+ to produce Ag2CrO4(s).
Why does the surface charge of a precipitate change sign at the equivalence point?
Describe how to analyze a solution of NaI by using the Volhard titration.

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