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engineering
chemical engineering
Questions and Answers of
Chemical Engineering
How would you prepare 1.00 L of a buffer with a pH of 7.00 from 0.200 M H3PO4 and 0.160 M NaOH?
Briefly explain why curve B cannot describe the titration of a mixture consisting of H3PO4 and NaH2PO4.
Formulate equilibrium constants for the following equilibria, and determine numerical values for the constants:(a)(b)
For pH values of 2.00, 6.00, and 10.00, calculate the alpha values for each species in an aqueous solution of*(a) Phthalic acid.(b) Phosphoric acid.*(c) Citric acid.(d) Arsenic acid.*(e) Phosphorous
Why is it impossible to titrate all three protons of phosphoric acid in aqueous solution?
Indicate whether an aqueous solution of the following compounds is acidic, neutral, or basic. Explain your answer.*(a) NH4OAc(b) NaNO2*(c) NaNO3(d) NaHC2O4*(e) Na2C2O4(f) Na2HPO4*(g) NaH2PO4(h) Na3PO4
Suggest an indicator that could be used to provide an end point for the titration of the first proton in H3AsO4.
Suggest a method for determining the amounts of H3PO4 and NaH2PO4 in an aqueous solution.
Suggest a suitable indicator for a titration based on each of the following reactions. Use 0.05 M if an equivalence point concentration is needed. *(a) H2CO3 + NaOH → NaHCO3 + H2O (b) H2P + 2NaOH
The concentration of a perchloric acid solution was established by titration against primary standard sodium carbonate (product: CO2); the following data were obtained.
A NaOH solution was 0.1019 M immediately after standardization. Exactly 500.0 mL of the reagent was left exposed to air for several days and absorbed 0.652 g of CO2. Calculate the relative carbonate
Calculate the molar concentration of a dilute Ba(OH)2 solution if (a) 50.00 mL yielded 0.1791 g of BaSO4. (b) Titration of 0.4512 g of primary standard potassium hydrogen phthalate (KHP) required
Calculate the relative standard deviation in the computed molar concentration of 0.0200 M HCl if this acid was standardized against the masses found in Example 16-1 for (a) TRIS, (b) Na2CO3, and (c)
A 50.00-mL sample of a white dinner wine required 24.57 mL of 0.03291 M NaOH to achieve a phenolphthalein end point. Express the acidity of the wine in grams of tartaric acid (H2C4H4O6; 150.09 g/mol)
Titration of a 0.7513-g sample of impure Na2B4O7 required 30.79 mL of 0.1129 M HCl. Express the results of this analysis in terms of percent (a) Na2B4O7. (b) Na2B4O7 ∙ 10H2O. (c) B2O3. (d) B.
The formaldehyde content of a pesticide preparation was determined by weighing 0.2985 g of the liquid sample into a flask containing 50.0 mL of 0.0959 M NaOH and 50 mL of 3% H2O2. Upon heating, the
The active ingredient in Antabuse, a drug used for the treatment of chronic alcoholism, is tetraethylthiuram disulfide,(296.54 g/mol). The sulfur in a 0.4169-g sample of an Antabuse preparation was
A 0.1401-g sample of a purified carbonate was dissolved in 50.00 mL of 0.1140 M HCl and boiled to eliminate CO2. Back-titration of the excess HCl required 24.21 mL of 0.09802 M NaOH. Identify the
A 3.00-L sample of urban air was bubbled through a solution containing 50.0 mL of 0.0116 M Ba(OH)2, which caused the CO2 in the sample to precipitate asBaCO3. The excess base was back-titrated to a
The boiling points of HCl and CO2 are nearly the same (285°C and 278°C). Explain why CO2 can be removed from an aqueous solution by boiling briefly while essentially no HCl is lost even after
The digestion of a 0.1417-g sample of a phosphorus-containing compound in a mixture of HNO3 and H2SO4 resulted in the formation of CO2, H2O, and H3PO4. Addition of ammonium molybdate yielded a solid
Neohetramine, C16H21ON4 (285.37 g/mol), is a common antihistamine. A 0.1247-g sample containing this compound was analyzed by the Kjeldahl method. The ammonia produced was collected in H3BO3-; the
A 0.917-g sample of canned tuna was analyzed by the Kjeldahl method. A volume of 20.59 mL of 0.1249 M HCl was required to titrate the liberated ammonia. Calculate the percentage of nitrogen in the
A 0.5843-g sample of a plant food preparation was analyzed for its N content by the Kjeldahl method, the liberated NH3 being collected in 50.00 mL of 0.1062 MHCl. The excess acid required an 11.89 mL
A 1.219-g sample containing (NH4)2SO4, NH4NO3, and nonreactive substances was diluted to 200 mL in a volumetric flask. A 50.00-mL aliquot was made basic with strong alkali, and the liberated NH3 was
A 0.5000-g sample containing NaHCO3, Na2CO3, and H2O was dissolved and diluted to 250.0 mL. A 25.00-mL aliquot was then boiled with 50.00 mL of 0.01255 M HCl. After cooling, the excess acid in the
Calculate the volume of 0.07731 M NaOH needed to titrate
A series of solutions containing NaOH, Na2CO3, and NaHCO3, alone or in compatible combination, was titrated with 0.1202 M HCl. Tabulated below are the volumes of acid needed to titrate 25.00-mL
Calculate the equivalent mass of oxalic acid dehydrate (H2C2O4 ∙ 2H2O, 126.066 g/mol) when it is titrated to (a) A bromocresol green end point and (b) A phenolphthalein end point.
Give two reasons why KH(IO3)2 is preferred over benzoic acid as a primary standard for a 0.010 M NaOH solution.
Briefly describe the circumstance where the concentration of a sodium hydroxide solution will apparently be unaffected by the absorption of carbon dioxide.
How would you prepare 2.00 L of (a) 0.10 M KOH from the solid? (b) 0.010 M Ba(OH)2 ∙ 8H2O from the solid? (c) 0.150 M HCl from a reagent that has a density of 1.0579 g/mL and is 11.50% HCl (w/w)?
Define (a) Ligand. (b) Tetradentate chelating agent. (c) Argentometric titration. (d) Edta displacement titration.
A solution contains 1.569 mg of CoSO4 (155.0 g/ mol) per milliliter. Calculate (a) The volume of 0.007840 M EDTA needed to titrate a 25.00-mL aliquot of this solution. (b) The volume of 0.009275 M
Calculate the volume of 0.0500 M EDTA needed to titrate (a) 29.13 mL of 0.0598 M Mg(NO3)2. (b) The Ca in a 0.4861-g mineral specimen that is 81.4% brushite, CaHPO4·2H2O (172.09 g/mol). (c) The Ca
The Zn in a 0.7457-g sample of foot powder was titrated with 22.57mL of 0.01639 M EDTA. Calculate the percent Zn in this sample.
A silver nitrate solution contains 14.77 g of primarystandard AgNO3 in 1.00 L. What volume of this solution will be needed to react with (a) 0.2631 g of NaCl? (b) 64.13 mg of Na3AsO4? (c) 25.00 mL of
What minimum volume of 0.09621 M AgNO3 will be needed to assure an excess of silver ion in the titration of (a) An impure NaCl sample that weighs 0.2513 g? (b) 25.00 mL of 0.01907 M AlCl3?
The Tl in a 9.57-g sample of rodenticide was oxidized to the trivalent state and treated with an unmeasured excess of Mg/EDTA solution. The reaction is Tl3+ + MgY2 → TlY- + Mg2+ Titration of the
A 50.00-mL aliquot of a solution containing iron(II) and iron(III) required 10.98 mL of 0.01500 M EDTA when titrated at pH 2.0 and 23.70 mL when titrated at pH 6.0. Express the concentration of each
A 1.509-g sample of a Pb/Cd alloy was dissolved in acid and diluted to exactly 250.0 mL in a volumetric flask. A 50.00-mL aliquot of the diluted solution was brought to a pH of 10.0 with a NH4+/NH3
Calamine, which is used for relief of skin irritations, is a mixture of zinc and iron oxides. A 1.056-g sample of dried calamine was dissolved in acid and diluted to 250.0 mL. Potassium fluoride was
A 3.650-g sample containing bromate and bromide was dissolved in sufficient water to give 250.0 mL. After acidification, silver nitrate was introduced to a 25.00-mL aliquot to precipitate AgBr, which
Describe three general methods for performing EDTA titrations. What are the advantages of each?
Chromel is an alloy composed of nickel, iron, and chromium. A 0.6553-g sample was dissolved and diluted to 250.0 mL. When a 50.00-mL aliquot of 0.05173 M EDTA was mixed with an equal volume of the
Titration of Ca2+ and Mg2+ in a 50.00-mL sample of hard water required 23.65 mL of 0.01205 M EDTA. A second 50.00-mL aliquot was made strongly basic with NaOH to precipitate Mg2+ as Mg(OH)2(s). The
Write chemical equations and equilibrium-constant expressions for the stepwise formation of Ag(S2O3)23-
Explain how stepwise and overall formation constants are related.
In what respect is the Fajans method superior to the Volhard method for the titration of chloride ion?
Why are multidentate ligands preferable to unidentate ligands for complexometric titrations?
Write equations in terms of the acid dissociation constants and [H+] for the highest alpha value for each of the following weak acid ligands: (a) Acetate (α1). (b) Tartrate (α2). (c) Phosphate
Given an overall complex formation reaction of M + nL ⇆ MLn, with an overall formation constant of βn, show that the following relationship holds: log βn = pM + npL - pMLn
Write a conditional overall formation constant for [Fe (ox)3]3- in terms of a2 for oxalic acid and the b value for the complex. Also express the conditional constant in terms of concentrations as in
Briefly describe or define (a) Oxidation. (b) Salt bridge. (c) Nernst equation.
Consider the following oxidation/reduction reactions:(a) Write each net process in terms of two balanced half-reactions. (b) Express each half-reaction as a reduction. (c) Arrange the half-reactions
Calculate the potential of a copper electrode immersed in (a) 0.0380 M Cu(NO3)2. (b) 0.0650 M in NaCl and saturated with CuCl. (c) 0.0350 M in NaOH and saturated with Cu(OH)2. (d) 0.0375 M in
If the following half-cells are the right-hand electrode in a galvanic cell with a standard hydrogen electrode on the left, calculate the cell potential. If the cell were shorted, indicate whether
Briefly describe or define (a) Electrode potential. (b) Standard electrode potential.
The solubility-product constant for Ag2SO3 is 1.5 Ã 10-14. Calculate E0 for the process
The solubility-product constant for Tl2S is 6 Ã 10-22. Calculate E0 for the reaction
Compute E0 for the process ZnY2- + 2e- ⇆ Zn(s) + Y4- Where Y4- is the completely deprotonated anion of EDTA, The formation constant for ZnY2- is 3.2 × 1016.
Given the formation constants Fe3+ + Y4- ⇆ FeY- Kf = 1.3 × 1025 Fe3+ + Y4- ⇆ FeY2- Kf = 2.1 × 1014 Calculate E0 for the process FeY- + e- ⇆ FeY2-
Make a clear distinction between (a) Oxidation and oxidizing agent. (b) The cathode of an electrochemical cell and the right-hand electrode. (c) The standard electrode potential and formal potential.
The following entries are found in a table of standard electrode potentials: I2(s) + 2e- ⇆ 2I- ................ E0 = 0.5355 V I2(aq) + 2e- ⇆ 2I- .............. E0 = 0.615 V
Write balanced net ionic equations for the following reactions. Supply H1 and/or H2O as needed to obtain balance. (a) Fe3+ + Sn2+ → Fe2+ + Sn4+ (b) Cr(s) + Ag+ → Cr3+ + Ag(s) (c) Ti3+ + Fe(CN)63-
Generate equilibrium constant expressions for the following reactions. Calculate numerical values for Keq.
Select an indicator from Table 19-3 that might be suitable for each of the titrations in Problem 19-11. Write NONE if no indicator listed in Table 19-3 is suitable.
How is an oxidation/reduction titration curve generated through the use of standard electrode potentials for the analyte species and the volumetric titrant?
Calculate the theoretical cell potential of the following cells. If the cell is short-circuited, indicate the direction of the spontaneous cell reaction. (a) Zn ( Zn2+ (0.1000 M) (( Co2+ (5.87 ( 10-4
Calculate the potential of the following two half-cells that are connected by a salt bridge: (a) A galvanic cell consisting of a lead electrode (right electrode) immersed in 0.0220 M Pb2+ and a zinc
Write balanced net ionic equations to describe(a) The oxidation of Mn2+ to MnO4- by ammonium peroxydisulfate.(b) The oxidation of U4+ to UO22+ by H2O2.(c) The titration of H2O2 with KMnO4.
Suggest a way in which a solution of KIO3 could be used as a source of known quantities of I2.
In the titration of I2 solutions with Na2S2O3, the starch indicator is never added until just before chemical equivalence. Why?
A solution prepared by dissolving a 0.2541-g sample of electrolytic iron wire in acid was passed through a Jones reductor. The iron(II) in the resulting solution required a 36.76-mL titration.
How would you prepare 1.000 L of 0.05000 M KBrO3?
A 0.2219-g sample of pure iron wire was dissolved in acid, reduced to the +2 state, and titrated with 34.65 mL of cerium(IV). Calculate the molar concentration of the Ce4+ solution.
Calculate the percentage of MnO2 in a mineral specimen if the I2 liberated by a 0.1267-g sample in the net reactionMnO2(s) + 4H+ + 2I- ( Mn2+ + I2 + 2H2ORequired 29.62 mL of 0.08041 M Na2S2O3.
Why is a Walden reductor always used with solutions that contain appreciable concentrations of HCl?
Treatment of hydroxylamine (H2NOH) with an excess of Fe(III) results in the formation of N2O and an equivalent amount of Fe(II):2H2NOH + 4Fe3+ ( N2O(g) + 4Fe2+ +4H+ + H2O
An 8.13-g sample of an ant-control preparation was decomposed by wet-ashing with H2SO4 and HNO3. The As in the residue was reduced to the trivalent state with hydrazine. After removal of the excess
A sensitive method for I¯ in the presence of Cl¯ and Br¯ entails oxidation of the I¯ to IO3¯ with Br¯. The excess Br¯ is then removed by boiling or by reduction with formate ion. The IO3¯
A gas mixture was passed at the rate of 2.50 L/min through a solution of sodium hydroxide for a total of 59.00 min. The SO2 in the mixture was retained as sulfite ion: SO2( g) + 2OH¯ ( SO32- +
The Winkler method for dissolved oxygen in water is based on the rapid oxidation of solid Mn(OH)2 to Mn(OH)3 in alkaline medium. When acidified, the Mn(III) readily releases iodine from iodide. A
Why are KMnO4 solutions filtered before they are standardized?
Briefly describe or define (a) Indicator electrode. (b) Electrode of the first kind.
What is the source of(a) The boundary potential in a membrane electrode?(b) The potential of a crystalline membrane electrode used to determine the concentration of F¯?
How does information supplied by a direct potentiometric measurements of pH differ from that obtained from a potentiometric acid/base titration?
(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
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) pPO4.
Calculate (a) pI if the cell in Problem 21-17(a) has a potential of - 196 mV. (b) pPO4 if the cell in Problem 21-17(c) has a potential of 0.211 V.
Briefly describe or define (a) Liquid-junction potential. (b) Asymmetry potential.
The cellSCE((Ag2CrO4 (sat'd), (x M) (Agis used for the determination of pCrO4. Calculate pCrO4 when the cell potential is 0.389 V.
The cell SCE((H+ (( = x) ( glass electrode
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 mLof 0.1243 M NaOH had been introduced.
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
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
Describe the source of pH dependence in a glass membrane electrode.
List several sources of uncertainty in pH measurements with a glass/calomel electrode system.
Describe the alkaline error in the measurement of pH. Under what circumstances is this error appreciable? How are pH data affected by alkaline error?
Briefly distinguish between (a) Concentration polarization and kinetic (b) Diffusion and migration. (c) The electrolysis circuit and the control circuit for controlled-potential methods.
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