Questions and Answers of Fundamentals Of Analytical Chemistry

A 25.00-mL sample of a household cleaning solution was diluted to 250.0 mL in a volumetric flask. A 50.00-mL aliquot of this solution required 43.04 mL of 0.1776 M HCl to reach a bromocresol green
A dilute solution of an unknown weak acid required a 28.94-mL titration with 0.1062 M NaOH to reach a phenolphthalein end point. The titrated solution was evaporated to dryness. Calculate the
Air was bubbled at a rate of 30.0 L/min through a trap containing 75 mL of 1% H2O2 (H2O2 + SO2 → H2SO4). After 10.0 minutes, the H2SO4 was titrated with 10.95 mL of 0.00242 M NaOH. Calculate
A 0.9826-g sample containing dimethyl phthalate, C6H4(COOCH3)2 (194.19 g/mol), and unreactive species was refluxed with 50.00 mL of 0.1104 M NaOH to hydrolyze the ester groups (this process is called
The Merck Index indicates that 10 mg of guanidine, CH5N3, may be administered for each kilogram of body mass in the treatment of myasthenia gravis. The nitrogen in a 4-tablet sample that had a total
A 0.8835-g sample of a wheat flour was analyzed by the Kjeldahl procedure. The ammonia formed was distilled into 50.00 mL of 0.05078 M HCl; a 8.04-mL back-titration with 0.04829 M NaOH was required.
A 1.421-g sample of commercial KOH contaminated by K2CO3 was dissolved in water, and the resulting solution was diluted to 500.0 mL. A 50.00-mL aliquot of this solution was treated with 40.00 mL of
Calculate the volume of 0.06452 M HCl needed to titrate(a) 20.00 mL of 0.05522 M Na3PO4 to a thymolphthalein end point.(b) 25.00 mL of 0.05522 M Na3PO4 to a bromocresol green end point.(c) 40.00 mL
A series of solutions containing NaOH, Na3AsO4, and Na2HAsO4, alone or in compatible combination, was titrated with 0.08601 M HCl. In the following table are the volumes of acid needed to titrate
A 10.00-mL sample of vinegar (acetic acid, CH3COOH) was pipetted into a flask, two drops of phenolphthalein indicator were added, and the acid was titrated with 0.1008 M NaOH.(a) If 45.62 mL of the
Write chemical equations and equilibrium-constant expressions for the stepwise formation of(a) Ag(S2O3)23–.(b) Cd(SCN)3–.(c) Ni(CN)42–.
Write chemical formulas for the following complex ions:(a) Hexamminezinc(II)(b) Dichloroargentate(c) Disulfatocuprate(II)(d) Trioxalatoferrate(III)(e) Hexacyanoferrate(II)
Calculate E0 for the process Cu(NH3)42+ + Cu(NH3)2 + 2 NH; given that Cut + 2NH3Cu(NH3)2 B2 = 7.2 X 10¹⁰ 2+ Cu²+ + 4NH3 = Cu(NH3)42+ B4 = 5.62 × 10¹¹
Briefly explain why the sparingly soluble product must be removed by filtration before you back-titrate the excess silver ion in the Volhard determination of(a) Chloride ion.(b) Cyanide ion.(c)
Outline a method for the determination of K+ based on argentometry. Write balanced equations for the chemical reactions.
How does calculation of the electrode potential of the system at the equivalence point differ from that for any other point of an oxidation/reduction titration?
Why are solutions of KMnO4 and Na2S2O3 generally stored in dark reagent bottles?
What is the primary use of standard K2Cr2O7 solutions?
A standard solution of I2 increased in concentration with standing. Write a balanced net ionic equation that accounts for the increase.
Write balanced equations showing how K2Cr2O7 could be used as a primary standard for solutions of Na2S2O3.
How would you prepare 2.0 L of approximately 0.04 MI3- solution? Calculate the molar concentration of KMnO4 in this solution.
A 0.1853-g sample of KBrO3 was dissolved in dilute HCl and treated with an unmeasured excess of KI. The liberated iodine required 44.36 mL of a sodium thiosulfate solution. Calculate the molar
The KClO3 in a 0.1791-g sample of an explosive was determined by reaction with 50.00 mL of 0.0873 M Fe2+When the reaction was complete, the excess Fe2+ was back-titrated with 14.95 mL of 0.06970 M
A 0.5690-g specimen of iron ore was dissolved and passed through a Jones reductor. Titration of the Fe(II) produced required 38.79 mL of 0.01926 M KMnO4. Express the results of this analysis in terms
The ethyl mercaptan concentration in a mixture was determined by shaking a 1.795-g sample with 50.00 mL of 0.01204 M I2 in a tightly stoppered flask:The excess I2 was back-titrated with 15.21 mL of
A 30.00-L air sample was passed through an absorption tower containing a solution of Cd2+, where H2S was retained as CdS. The mixture was acidified and treated with 10.00 mL of 0.0100 M I2. After the
A 2.552-g sample containing both Fe and V was dissolved under conditions that converted the elements to Fe(III) and V(V). The solution was diluted to 500.0 mL, and a 50.00-mL aliquot was passed
Use a spreadsheet to do the calculations and plot the titration curves for the following titrations. Calculate potentials after the addition of titrant corresponding to 10%, 20%, 30%, 40%, 50%, 60%,
What is meant by Nernstian behavior in an indicator electrode?
Why is it necessary for the glass in the membrane of a pH-sensitive electrode to be appreciably hygroscopic?
How does a gas-sensing probe differ from other membrane electrodes?
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,
What is the principle of micellar electrokinetic capillary chromatography? How does it differ from capillary zone electrophoresis?
Describe a major advantage of micellar electrokinetic capillary chromatography over conventional liquid chromatography.
What determines the elution order in sedimentation FFF?
Propose a complexometric method for the determination of the individual components in a solution containing In3+, Zn2+, and Mg2+.
Why is a small amount of MgY2– often added to a water specimen that is to be titrated for hardness?
A solution was prepared by dissolving about 3.0 g of Na2H2Y . 2H2O in approximately 1 L of water and standardizing against 50.00-mL aliquots of 0.00397 M Mg2+. An average titration of 30.27 mL was
A Fajans titration of a 0.7908-g sample required 29.32 mL of 0.1620 M AgNO3. Express the results of this analysis in terms of the percentage of(a) Cl-.(b) BaCl2 . H2O.(c) ZnCl2 . 2NH4Cl (243.28
An EDTA solution was prepared by dissolving approximately 4 g of the disodium salt in approximately 1 L of water. An average of 37.99 mL of this solution was required to titrate 50.00-mL aliquots of
A 24-hour urine specimen was diluted to 2.000 L. After the solution was buffered to pH 10, a 10.00-mL aliquot was titrated with 23.57 mL of 0.004590 M EDTA. The calcium in a second 10.00-mL aliquot
A 0.6004-g sample of Ni/Cu condenser tubing was dissolved in acid and diluted to 100.0 mL in a volumetric flask. Titration of both cations in a 25.00-mL aliquot of this solution required 45.81 mL of
A 0.3304-g sample of brass (containing lead, zinc, copper, and tin) was dissolved in nitric acid. The sparingly soluble SnO2 . 4H2O was removed by filtration, and the combined filtrate and washings
Why is it necessary to bubble hydrogen through the electrolyte in a hydrogen electrode?
Calculate conditional constants for the formation of the EDTA complex of Fe2+ at a pH of (a) 6.0, (b) 8.0,(c) 10.0.
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 in
Use activities to calculate the electrode potential of a hydrogen electrode in which the electrolyte is 0.0200 M HCl and the activity of H2 is 1.00 atm.
Calculate the potential of a platinum electrode immersed in a solution that is(a) 0.0513 M in K4Fe(CN)6 and 0.00589 M in K3Fe(CN)6.(b) 0.0300 M in FeSO4 and 0.00825 M in Fe2(SO4)3.(c) Buffered to a
The following half-cells are on the left and coupled with the standard hydrogen electrode on the right to form a galvanic cell. Calculate the cell potential. Indicate which electrode would be the
The solubility-product constant for Ni2P2O7 is 1.7 x 10-13. Calculate E0 for the process Ni₂P₂O7(s) + 4c = 2Ni(s) + P₂O₂¹ P₂0,4-
The solubility product for Pb3(AsO4)2 is 4.1 x 10-36. Calculate E0 for the reaction Pb₂(AsO4)2(s) + Ge = 3Pb(s) + 2AsO4²-
For a Pt | Fe3+, Fe2+ half-cell, find the potential for the following ratios of [Fe3+]/[Fe2+]: 0.001, 0.0025, 0.005, 0.0075, 0.010, 0.025, 0.050, 0.075, 0.100, 0.250, 0.500, 0.750, 1.00, 1.250, 1.50,
For an oxidation/reduction titration, briefly distinguish between(a) Equilibrium and equivalence.(b) A true oxidation/reduction indicator and a specific indicator.
What is unique about the condition of equilibrium in an oxidation/reduction reaction?
Calculate the theoretical potential of the following cells. Indicate whether the reaction will proceed spontaneously in the direction considered (oxidation on the left; reduction on the right) or
Under what circumstance is the curve for an oxidation/ reduction titration asymmetric about the equivalence point?
Write a balanced net ionic equation for the reduction of UO22+ in a Walden reductor.
Why are standard solutions of reductants less often used for titrations than standard solutions of oxidants?
Why are Ce4+ solutions never used for the titration of reductants in basic solutions?
Before glass electrodes and pH meters became widely used, pH was often determined by measuring the concentration of the acid and base forms of the indicator colorimetrically. If bromothymol blue is
The equilibrium constant for the conjugate acid-base pairis 8.00 x 10-5. From the additional information(a) Calculate the absorbance at 430 nm and 600 nm for the following indicator concentrations:
Three large proteins are ionized at the pH at which an electrical FFF separation is carried out. If the ions are designated A2+, B+, and C3+, predict the order of elution.
List the major advantages and limitations of FFF compared to chromatographic methods.
Give several advantages of a potentiometric titration over a direct potentiometric measurement.
What is the “operational definition of pH”? Why is it used?
A 40.00-mL aliquot of 0.05000 M HNO2 is diluted to 75.00 mL and titrated with 0.0800 M Ce4+. The pH of the solution is maintained at 1.00 throughout the titration; the formal potential of the cerium
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
Why is gas-solid chromatography not used as extensively as gas-liquid chromatography?
List the types of substances to which each of the following chromatographic methods is most applicable:(a) Gas-liquid.(b) Liquid-liquid.(c) Ion.(d) Adsorption.(e) Gel permeation.(f) Affinity.(g)
Indicate the order of elution of the following compounds from a normal phase packed HPLC column:(a) Ethyl acetate, acetic acid, dimethylamine.(b) Propylene, hexane, benzene, dichlorobenzene.
Describe the fundamental difference between ionexchange and size-exclusion chromatography.
What types of species can be separated by GC but not by HPLC?
Describe two types of pumps used in HPLC. What are the advantages and disadvantages of each?
Mass spectrometry is an extremely versatile detection system for gas chromatography. Describe the major reasons why it is more difficult to combine HPLC with mass spectrometry than it is to combine
Two components in an HPLC separation have retention times that differ by 22 s. The first peak elutes in 10.5 minutes, and the peak widths are approximately equal. The void time, tM, was 63 s. Use a
Describe the effect of pressure on supercritical fluid chromatography.
List some of the advantageous properties of supercritical CO2 as a mobile phase for chromatographic separations.
What important property of supercritical fluids is related to their densities?
Compare supercritical fluid chromatography with other column chromatographic methods.
What is the effect of pH on the separation of amino acids by electrophoresis? Why?
How could electroosmotic flow be repressed? Why would one want to repress it?
A certain inorganic cation has a electrophoretic mobility of 6.97 x 10-4 cm2 s-1 V-1. This same ion has a diffusion coefficient of 7.8 x 10-6 cm2 s-1. If this ion is separated by capillary zone
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
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
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
Describe three mechanisms responsible for the transport of dissolved species to and from an electrode surface.
How does a current in an electrochemical cell affect its potential?
What experimental variables affect concentration polarization in an electrochemical cell?
How do concentration polarization and kinetic polarization resemble one another? How do they differ?
What is a supporting electrolyte, and what is its role in electrochemistry?
What is the purpose of a depolarizer?
Why is the working electrode normally isolated from the counter electrode in a controlled-potential coulometric analysis?
Why is an auxiliary reagent always required in a coulometric titration?
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+
A solution is 0.0350 M in BiO+ and 0.0250 M in Co2+ and has a pH of 2.50.(a) What is the concentration of the more easily reduced cation at the onset of deposition of the less reducible one?(b) What
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
Electro gravimetric analysis with control of the cathode potential is proposed as a means for separating Bi31 and Sn21 in a solution that is 0.250 M in each ion and buffered to pH 1.95.(a) Calculate
Calculate the time needed for a constant current of 1.25 A to deposit 0.550 g of(a) Tl(III) as the element on a cathode.(b) Tl(I) as Tl2O3 on an anode.(c) Tl(I) as the element on a cathode.
At a potential of -1.0 V (versus SCE), CCl4 in methanol is reduced to CHCl3 at a mercury cathode:Several different 0.750-g samples containing CCl4, CHCl3, and inert organic species were dissolved in
The CN- concentration of 10.0 mL of a plating solution was determined by titration with electrogenerated hydrogen ion to a methyl orange end point. A color change occurred after 3 minutes and 55 s

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