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quantitative chemical analysis 9th edition
Quantitative Chemical Analysis 9th Edition Daniel C. Harris - Solutions
Cathodic stripping of ClO-4 in Figure 17-26 does not involve oxidation or reduction of ClO-4. Explain how this measurement works.In Figure 17-26 To potentiostat Teflon Spin entire electrodo rapidly holder Au electrode Oxidize polymor film Reduce polymer film Reduced Oxidized poly(3-octylthiophene)
In 1 M NH3/1 M NH4Cl solution, Cu2+ is reduced to Cu+ near 20.3 V (versus S.C.E.), and Cu+ is reduced to Cu(in Hg) near 20.6 V.(a) Sketch a qualitative sampled current polarogram for a solution of Cu+.(b) Sketch a polarogram for a solution of Cu2+.(c) Suppose that Pt, instead of Hg, were used as
Explain why each voltammogram from the rotating disk electrode in Figure 17-16 reaches a plateau at low potential and at high potential. What chemistry occurs in each plateau? Why do all the curves overlap at low potential? How might the current density in each plateau change if the rotation speed
In Figure 17-11, 2.00 nmol of fructose were introduced at the time of the arrow. How many electrons are lost in the oxidation of one molecule of fructose? Compare the theoretical number of coulombs with the observed number of coulombs for complete oxidation of the sample.In figure 17-11 10 8
(a) The cell in Figure 17-4 is: Cu(s) |1.0 M CuSO4(aq) A KCl (aq, 3 M) | AgCl(s) | Ag(s) Write half-reactions for this cell. Neglecting activity coefficients and the junction potential between CuSO4(aq) and KCl (aq), predict the equilibrium (zero-current) voltage expected when the Luggin capillary
The pathogenic bacterium Salmonella enterica uses tetrathionate found in the human gut as an oxidant— just as we use O2 to metabolize our food. 34 Write the half-reaction in which tetrathionate serves as an oxidant. Is tetrathionate as powerful an oxidant as O2?
Consider the titration of 25.0 mL of 0.010 0 M Sn2+ by 0.050 0 M Tl3+ in 1 M HCl, using Pt and saturated calomel electrodes to find the end point.(a) Write a balanced titration reaction.(b) Write two different half-reactions for the indicator electrode.(c) Write two different Nernst equations for
A 50.00-mL sample containing La3+ was treated with sodium oxalate to precipitate La2(C2O4)3, which was washed, dissolved in acid, and titrated with 18.04 mL of 0.006 363 M KMnO4. Write the titration reaction and find [La3+] in the unknown.
(a) Explain why the diffusion coefficient of CH3OH is greater than that of sucrose in Table 23-1.(b) Make an order-of-magnitude estimate of the diffusion coefficient of water vapor in air at 298 K.Table 23-1 TABLE 23-1 Representative diffusion coefficients at 298 K Solute Solvent Diffusion
Consider the titration of 100.0 mL of 0.010 0 M Ce4+ in 1 M HClO4 by 0.040 0 M Cu+ to give Ce3+ and Cu2+, using Pt and saturated Ag | AgCl electrodes to find the end point. (a) Write a balanced titration reaction. (b) Write two different half-reactions for the indicator electrode.(c)
A 20.0-mL solution of 0.005 00 M Sn2+ in 1 M HCl was titrated with 0.020 0 M Ce4+ to give Sn4+ and Ce3+. Calculate the potential (versus S.C.E.) at the following volumes of Ce4+: 0.100, 1.00, 5.00, 9.50, 10.00, 10.10, and 12.00 mL. Sketch the titration curve.
Explain how the device at the opening of this chapter measures the sequence of nucleotide bases in DNA. What is the purpose of the chemically sensitive field effect transistor in the device?
Standard addition with confidence interval. Ammonia in seawater was measured with an ammonia-selective electrode. A 100.0 mL aliquot of seawater was treated with 1.00 mL of 10 M NaOH to convert NH+4 to NH3. Therefore, V0 = 101.0 mL. A reading was then taken with the electrode. Then 10.00-mL
The selectivity coefficient, KPot Li+, H+, for a Li+ ion-selective electrode is 4 × 10-4. When this electrode is placed in 3.44 × 10-4 M Li+ solution at pH 7.2, the potential is 20.333 V versus S.C.E. What would be the potential if the pH were lowered to 1.1 and the ionic strength were kept
Why do the liquid junctions potentials 0.1 M HCl | 0.1 M KCl and 0.1 M NaOH | 0.1 M KCl have opposite signs in Table 15-2? Why is the junction potential for 0.1 M NaOH | 0.1 M KCl so much more negative than 0.1 M NaOH | KCl (saturated)? TABLE 15-2 Estimated liquid junction potentials at 25°C
Consider the cell S.C.E. i cell solution | Pt(s), whose voltage is 20.126 V. The cell solution contains 2.00 mmol of Fe(NH4)2(SO4)2, 1.00 mmol of FeCl3, 4.00 mmol of Na2EDTA, and lots of buffer, pH 6.78, in a volume of 1.00 L.(a) Write a reaction for the right half-cell.(b) Find the quotient
What is electroosmosis?
(a) What are the advantages and disadvantages of temperature programming in gas chromatography?(b) What is the advantage of pressure programming?
(a) What types of solutes are typically separated with a poly(dimethylsiloxane)-coated open tubular column?(b) What types of solutes are typically separated with a poly(ethylene glycol)-coated open tubular column?(c) What types of solutes are typically separated with a porous-layer open tubular
(a) What are the advantages and disadvantages of using a narrower open tubular column?(b) What are the advantages and disadvantages of using a longer open tubular column?(c) What are the advantages and disadvantages of using a thicker film of stationary phase?
Why do open tubular columns provide greater resolution than packed columns in gas chromatography?
In chromatography, why is the optimal flow rate greater if the stationary phase particle size is smaller?
Why is longitudinal diffusion a more serious problem in gas chromatography than in liquid chromatography?
In chromatography, resolution is governed by (a) The number of plates, (b) Relative retention, and (c) Retention factor. Construct a set of graphs to show the dependence of resolution on each of these three parameters. Comment on the nature of the dependence of resolution on
The partition coefficient for a solute in chromatography is K = cs /cm, where cs is the concentration in the stationary phase and cm is the concentration in the mobile phase. The larger the partition coefficient, the longer it takes a solute to be eluted. Explain why.
Match the terms in the first list with the characteristics in the second list.1. Adsorption chromatography2. Partition chromatography3. Ion-exchange chromatography4. Molecular exclusion chromatography5. Affinity chromatographyA. Ions in mobile phase are attracted to counterions covalently attached
The solute in Problem 23-8 is initially dissolved in 80.0 mL of water. It is then extracted six times with 10.0-mL portions of chloroform. Find the fraction of solute remaining in the aqueous phase.Data from Problem 23-8Solute S has a partition coefficient of 4.0 between water (phase 1) and
The three chromatograms shown here were obtained with 2.5, 1.0, and 0.4 mL of ethyl acetate injected on the same column under the same conditions. Explain why the peak becomes less symmetrical with increasing sample size. 2.5 μL 1.0 μL 0.4 μL Time -
A gas chromatogram of a mixture of toluene and ethyl acetate is shown here.(a) Use the width of each peak (measured at the base) to calculate the number of theoretical plates in the column. Estimate all lengths to the nearest 0.1 mm. (b) Using the width of the toluene peak at its base,
If you wish to extract aqueous acetic acid into hexane, is it more effective to adjust the aqueous phase to pH 3 or pH 8?
When performing liquid-liquid extraction, it is common practice to shake the separatory funnel to disperse one phase into the other.(a) Does shaking the separatory funnel change the partition coefficient?(b) Explain the purpose of shaking the funnel.
If you are extracting a substance from water into ether, is it more effective to do one extraction with 300 mL of ether or three extractions with 100 mL?
A solute with a partition coefficient of 4.0 is extracted from 10 mL of phase 1 into phase 2. (a) What volume of phase 2 is needed to extract 99% of the solute in one extraction?(b) What is the total volume of solvent 2 needed to remove 99% of the solute in three equal extractions instead?
Why does vacuum ultraviolet photoionization with |120-nmwavelength radiation produce less molecular fragmentation than does 70 eV electron ionization?
Which liquid chromatography/mass spectrometry interface, atmospheric pressure chemical ionization or electrospray, requires analyte ions to be in solution prior to the interface? How does the other interface create gaseous ions from neutral species in solution?
If ions are accelerated through 20 kV in the source of a time-of- flight mass spectrometer with a 2.00 m drift distance, what are the transit times of ions with m/z = 100 and m/z = 1 000 000?
Calculate Eo' for the reaction H2C204 + 2H+ + 2e 2HCO,H E° = 0.204 V Oxalic acid Formic acid
Evaluate Eo' for the half-reaction (CN)2(g) + 2H* + 2e = 2HCN(aq) Cyanogen Hydrogen cyanide
Explain what Eo' is and why it is preferred over Eo in biochemistry.
The following cell was constructed to fi nd the difference in Ksp between two naturally occurring forms of CaCO3(s), called calcite and aragonite.Each compartment of the cell contains a mixture of solid PbCO3 (Ksp = 7.4 × 10-14) and either calcite or aragonite, both of which have Ksp < 5
Given the following information, calculate the standard potential for the reaction FeY- + e- ⇋ FeY2-, where Y is EDTA. FeY + e = Fe?+ + Y4- E° = -0.730 V FeY?-: Kf = 2.1 x 1014 FeY: K = 1.3 x 1025
A solution contains 0.100 M Ce3+, 1.00 × 1024 M Ce4+, 1.00 × 1024 M Mn2+, 0.100 M MnO4- , and 1.00 M HClO4.(a) Write a balanced net reaction that can occur between species in this solution.(b) Calculate DGo and K for the reaction.(c) Calculate E for the conditions given.(d) Calculate DG for the
For the reaction CO + 1/2 O2 ⇋ CO2, DGo = -257 kJ per mole of CO at 298 K. Find Eo and the equilibrium constant for the reaction.
Cabin air in the Apollo spacecraft was circulated through a canister of solid LiOH to remove CO2 to prevent poisoning the astronauts with excess CO2. Write the chemical reaction between LiOH(s) and CO2(g). Why was LiOH used instead of the less expensive NaOH or KOH?
What must be the relation between Eo+ and Eo- if the species X+ is to diproportionate spontaneously under standard conditions to X3+ and X(s)? Write a balanced equation for the disproportionation.
Write a balanced chemical equation (in acidic solution) for the reaction represented by the question mark.22 As in Box 14-5, calculate Eo for the reaction. 1.441 1.491 1.584 1.098 BrO,- → HOB - НОВГ- Br,(aq) - » Br,(aq) Br
(a) Write the Nernst equations for the half-reactions in Demonstration 14-1. In which direction do electrons move through the circuit?(b) If you use your fingers as a salt bridge in Demonstration 14-1, will your body take in Cu2+ or Zn2+?
What is the difference between E and Eo for a redox reaction? Which one runs down to 0 when the complete cell comes to equilibrium?
Considering just acid-base chemistry, not ion pairing and not activity coefficients, use the systematic treatment of equilibrium to find the pH and concentrations of species in 1.00 L of solution containing 0.100 mol ethylenediamine and 0.035 mol HBr. Compare the pH to that found by the methods of
A 50.0-mL solution containing Ni2+ and Zn2+ was treated with 25.0 mL of 0.045 2 M EDTA to bind all the metal. The excess unreacted EDTA required 12.4 mL of 0.012 3 M Mg2+ for complete reaction. An excess of the reagent 2,3-dimercapto-1- propanol was then added to displace the EDTA from zinc.
Suppose that 0.010 0 M Mn2+ is titrated with 0.005 00 M EDTA at pH 7.00. (a) What is the concentration of free Mn2+ at the equivalence point?(b) What is the quotient [H3Y-]/[H2Y2-] in the solution when the titration is just 63.7% of the way to the equivalence point?
Why are many ionic precipitates washed with electrolyte solution instead of pure water?
A 25.00-mL sample containing Fe3+ and Cu2+ required 16.06 mL of 0.050 83 M EDTA for complete titration. A 50.00-mL sample of the unknown was treated with NH4F to protect the Fe3+. Then Cu21 was reduced and masked by thiourea. Addition of 25.00 mL of 0.050 83 M EDTA liberated Fe3+ from its fluoride
How does solid-supported liquid-liquid extraction differ from solid-phase extraction?
(a) Explain how dispersive liquid-liquid microextraction reduces the use of solvent in comparison with liquid-liquid extraction.(b) What is the purpose of the disperser solvent, which is used in much greater volume than the extraction solvent?
Explain what is meant by the statement, “Unless the complete history of any sample is known with certainty, the analyst is well advised not to spend his or her time in analyzing it.”
Why is it less desirable to wash AgCl precipitate with aqueous NaNO3 than with HNO3 solution?
Explain what is done in thermogravimetric analysis.
A mixture containing only aluminum tetrafl uoroborate, Al(BF4)3 (FM 287.39), and magnesium nitrate, Mg(NO3)2 (FM 148.31), weighed 0.282 8 g. It was dissolved in 1 wt% HF(aq) and treated with nitron solution to precipitate a mixture of nitron tetrafluoroborate and nitron nitrate weighing 1.322 g.
Why is high relative supersaturation undesirable in a gravimetric precipitation?
State four desirable properties of a gravimetric precipitate.
(a) What is the difference between absorption and adsorption?(b) How is an inclusion different from an occlusion?
Would molecular exclusion, affinity, or hydrophobic interaction chromatography be most appropriate for each of the following applications?(a) Purifying and concentrating a crude mixture of an antibody.(b) Desalting a solution containing a 30 kDa protein.(c) Finding the molecular mass distribution
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. The table lists concentrations of anions and cations measured in pond water in an undergraduate experiment and expressed in
What does the designation 200/400 mesh mean on a bottle of chromatography stationary phase? What is the size range of such particles? Which particles are smaller, 100/200 or 200/400 mesh?
State the effects of increasing cross-linking on an ion exchange column.
Human serum albumin (HSA) is an important protein ingredient in cryopreservation media used in procedures such as in vitro fertilization. Search the literature for a highperformance liquid chromatography method for the determination of human serum albumin and the stabilizer N-acetyltryptophan in
The purity of cocaine bought on the street varies dramatically. Cutting agents include levamisole, a compound normally used to kill parasites. Search the literature for a reversed-phase liquid chromatography method with diode array detection for the determination of the purity of street cocaine.(a)
A reversed-phase separation of a reaction mixture calls for isocratic elution with 48% methanol/52% water. If you want to change the procedure to use acetonitrile/water, what is a good starting percentage of acetonitrile to try?
To which kinds of analytes do these liquid chromatography detectors respond?(a) Ultraviolet(b) Refractive index(c) Evaporative light scattering(d) Charged aerosol(e) Electrochemical(f) Fluorescence(g) Nitrogen chemiluminescence(h) Conductivity
How do additives such as triethylamine reduce tailing of certain solutes?
(a) Why are HPLC particles porous?(b) Why are particles with 60- to 120-Å pores used for small molecules but wide-pore 300-Å stationary phases used to separate polypeptides and proteins?
(a) Why is high pressure needed in HPLC?(b) For a given column length, why do smaller particles give a higher plate number?(c) What is a bonded phase in liquid chromatography?
In hydrophilic interaction chromatography (HILIC), why is eluent strength increased by increasing the fraction of water in the mobile phase?
A known mixture of compounds A and B gave the following HPLC results:A solution was prepared by mixing 12.49 mg of B plus 10.00 mL of unknown containing just A and diluting to 25.00 mL. Peak areas of 5.97 and 6.38 were observed for A and B, respectively. Find the concentration of A (mg/mL) in the
Oxalate is a naturally occurring substance found in plant foods such as fruits and vegetables. Within the body it can combine with calcium to form kidney or urinary stones. Determination of oxalate in food is important because of the potential for harmful effects on health. Search the literature
(a) How can you improve the resolution between two closely spaced peaks in gas chromatography?(b) What approach from (a) would be most cost effective (not involve a purchase)?
The burning of fossil fuel by humans in 2012 introduced approximately 8 petagrams (Pg) of carbon per year into the atmosphere in the form of CO2.(a) How many kg of C are placed in the atmosphere each year?(b) How many kg of CO2 are placed in the atmosphere each year?(c) A metric ton is 1 000 kg.
A solution with a final volume of 500.0 mL was prepared by dissolving 25.00 mL of methanol (CH3OH, density = 0.791 4 g/mL) in chloroform.(a) Calculate the molarity of methanol in the solution.(b) The solution has a density of 1.454 g/mL. Find the molality of methanol.
(a) An aqueous solution contains 12.6 ppm of dissolved Ca(NO3)2 (which gives Ca2+ + 2NO-3). Find the concentration of NO-3 in parts per million.(b) How many ppm of Ca(NO3)2 are in 0.144 mM Ca(NO3)2?(c) How many ppm of nitrate (NO-3) are in 0.144 mM Ca(NO3)2?
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