Practice Final Exam

CH271 Practice Final Exam 1. In selecting a substance to serve as a primary standard, which always is essential?

a. The substance must have a high equivalent weight. b. The substance must be thermally stable at 110º C. c. The substance must be a strong acid or base. d. The substance must have an accurately known purity.

2. When the absorbance of a solution containing two non-reactive components is measured at a wavelength where both components absorb light,

a. the components absorb light in equal amounts. b. the components absorb light independently of each other. c. the absorbance is independent of concentration. d. the components must be chemically separated before the absorbance can be used in analysis.

3. The weak acid H3X has the following pKa values: pKa1 = 3.00, pKa2 = 5.00, pKa3 = 7.00. At pH 6.00 what is the predominate species?

a. H3X - b. H2X c. HX2- d. X3-

4. In replicate analyses on the same size sample, one buret reading is 40.88 ml. Which buret reading deviates by two parts per thousand from the first?

a. 40.08 b. 40.48 c. 40.80 d. 40.84

5. Precipitating agents used in gravimetric determinations should

a. be in the form of a dilute solution. b. be added all at once. c. form soluble complexes with the material being analyzed. d. contain the anion of a weak acid. 6. Which is the concentration of oxalate ion in equilibrium with a precipitate of silver -11 oxalate if the solution is 0.010 M in AgNO3? Ksp (Ag2C2O4) = 1.3 x 10

a. 1.3 x 10-15 M b. 1.0 x 10-10 M c. 1.3 x 10-7 M d. 2.6 x 10-9 M

7. It is desired to prepare 1 liter of a formic acid-formate buffer solution of pH = 3.75. Starting with 1 liter of a 0.200 M solution of formic acid how many grams of solid sodium formate would have to be added, assuming no volume change when the addition is made?

-4 Given: Ka for HCOOH = 1.76 x 10 Mol. Wt. HCOOH = 46.0 Mol. Wt. HCOONa = 68.0

a. 13.5 g b. 26.3 g c. 37.5 g d. 68.0 g

8. From the list of acids and their ionization constants select the best acid (and its salt) to produce a buffer solution of pH 6.0.

-3 a. phthalic acid, first ionization (Ka = 1.3 x 10 ) -4 b. formic acid (Ka = 1.7 x 10 ) -5 c. benzoic acid (Ka = 6.3 x 10 ) -6 d. phthalic acid, second ionization (Ka2 = 3.9 x 10 )

9. Given for H3PO4

-3 Ka1 = 7.00 x 10 ; pKa1 = 2.16 -8 Ka2 = 7.00 x 10 ; pKa2 = 7.16 -13 Ka3 = 5.00 x 10 ; pKa3 = 12.3

What is the pH of a 0.100 M Na2HPO4 solution?

a. 7.16 b. 9.73 c. 10.2 d. 12.3 10. A solution contains two weak acids, HY and H2Z, dissolved in water and made up to 500 ml in a volumetric flask. A single 50.0 ml aliquot titrated with 0.100 M NaOH yields two equivalence points, the first at 10.0 ml addition of standard base and the second at 35.0 ml total addition of titrant.

-8 Given: HY, Ka = 5.90 x 10 -2 H2Z, Ka1 = 1.20 x 10 -8 Ka2 = 6.10 x 10

How many millimoles of the acids H2Z and HY, respectively, were dissolved in the original 500 mL of solution?

a. 10.0 and 25.0 b. 10.0 and 35.0 c. 10.0 and 15.0 d. 0.0100 and 0.0150 e. None of these is correct.

11. Which is an essential requirement in order that a reaction be suitable for a quantitative titration?

a. A visual indicator must be available for signaling the arrival of the equivalence point. b. The reaction must be at least 99.9 percent complete. c. The reaction must not require more than fifteen minutes to reach equilibrium d. The end point must correspond exactly to the equivalence point.

12. Which statement concerning the titration of a halide ion with silver nitrate using an adsorption indicator is not true?

a. The indicator anion, IN-, must not displace the primary adsorbed ion, X-, during the titration. b. Large particle size (small-surface area) is desirable. c. The pH must not be too low because of its effect upon the indicator equilibrium. d. Diffuse light is desirable to minimize photodecomposition of silver halide. 13. Butyl hydroperoxide (C4H9OOH, FW = 90.0 g/mol) is determined by reaction with excess potassium iodide followed by titration of the iodine formed with sodium thiosulfate:

- + C4H9OOH + 2I + 2H → C4H9OH + I2 + H2O

2- 2- - 2S2O3 + I2 → S4O6 + 2I

A 315.0 mg sample containing butyl hydroperoxide requires 18.20 mL of 0.1000 M sodium thiosulfate for the final titration. Calculate the percentage of butyl hydroperoxide in the sample.

a. 13.0 % b. 26.0 % c. 39.0 % d. 40.0 %

14. A chelate complex absorbs energy at 540 nm. Using a 1.00 cm cell one finds that a 2.50 x 10-5 M solution of the chelate has an absorbance of 0.755 and a 1.00 x 10-5 M solution has an absorbance of 0.302. What is the molar absorbtivity of the complex?

a. 1.89 x 10-5 b. 7.50 c. 15,100 d. 30,200

15. To prepare and standardize one liter of approximately 0.1 M KOH from an aqueous stock solution which is 50.0 per cent by weight in KOH ( FW = 56.1 g/mol) and has a density of 1.50 g/mL, approximately how much KOH solution should be taken for dilution? (mol. wt. KOH = 56.1)

a. 17 mL b. 8.0 mL c. 7.5 mL d. 5.6 mL

16. If 0.50 mole of Na3PO4 is mixed with 0.30 mole of BaCl2, the maximum number of moles of barium phosphate which can be formed is

a. 0.10 b. 0.15 c. 0.30 d. 0.50 17. In an experiment to study apparent deviation from Beer’s Law, two separate bands of polychromatic radiation were employed as indicated on the graph below.

BA 0.5

0.3 e c n a b

r 0.25 o s b A 0.2 A

0.05 B 0 400 420 440 460 480 500 520 540 560 580 600 620 Wavelength (nm)

Which statement correctly describes the resultant plots of absorbance as a function of concentration of the compound being studied?

a. A straight line plot is obtained in both cases as long as the species under study does not change as a function of concentration. b. Neither plot will give a straight line plot unless the absorbance values are converted to per cent transmittance before plotting. c. Only data obtained using band A will give a straight line plot. Data from the use of band B will show negative deviations from Beer’s law. d. The correct answer is not given.

18. According to the Bronsted theory, which species is most likely to function both as an acid and as a base?

a. Cl- + b. NH4 - c. HCO3 + d. H3O 19. In the given reaction, which substances are the bases according to the Bronsted definition?

+ - HC2H3O2 + H2O → H3O + C2H3O2

a. HC2H3O2 and H2O - b. HC2H3O2 and C2H3O2 - c. H2O and C2H3O2 + - d. H3O and C2H3O2

20. How many moles of pure NaOH must be used to prepare 10 liters of a solution that has a pH of 13?

a. 1.0 b. 0.10 c. 0.010 d. 0.0010

21. A 0.20 M solution of the hypothetical weak acid HZ is found to have a pH of exactly 3.0. The ionization constant, Ka, of the acid HZ is

a. 0.6 b. 1.0 x 10-3 c. 2.0 x 19-4 d. 5.0 x 10-6 22. The titration curve for an equimolar mixture of acetic acid (HOAc) and hydrochloric acid (HC1) with an aqueous sodium hydroxide (NaOH) solution would have which of the following shapes. a.

8 H p 6

0 0 10 20 30 40 50 60 70 b.

8 H p 6

0 0 10 20 30 40 50 60 70 c.

8 H p 6

0 0 10 20 30 40 50 60 70 d.

8 H p 6

0 0 10 20 30 40 50 60 70 23. What must be the acetate:acetic acid ratio in order to provide a solution of pH 5? -5 Ka of acetic acid = 1.8 x 10 .

a. 0.056 b. 1.0 c. 1.8 d. 5.0

24. What is the hydrogen ion concentration of a solution 0.100 M in HCN and -10 0.0500 M in KCN? Ka of HCN = 4.93 x 10

a. 9.86 x 10-5 M b. 9.86 x 10-10 M c. 4.93 x 10-10 M d. 2.46 x 10-10 M

25. Calculate the pH of a 0.150 M solution of the weak base trimethylamine, (CH3)3N, -5 for which Kb = 6.45 x 10 .

a. 13.2 b. 12.3 c. 11.5 d. 2.51

26. It is desired to titrate a mixture of hydrochloric, nitric, and hydrobromic acids (all of which are strong acids in water) to yield three distinct end points. Which of the following would represent the most suitable medium for performing such a titration?

a. Glacial acetic acid b. Anhydrous ammonia c. Anhydrous methanol d. Water

27. The strongest acid capable of existence in anhydrous HF is

a. HF + b. H2F + c. H3O d. HC1 28. A 50.0 mL aliquot of a sulfuric acid solution was treated with barium chloride and the resulting BaSO4 was isolated and weighed. If 0.667 gram of BaSO4 was obtained what is the molarity of the H2SO4? Mol.wt. BaSO4 = 233.

a. 0.00700 M b. 0.0286 M c. 0.0572 M d. 1.43 M

29. Barium ion is reacted with KIO3 solution to form Ba(IO3)2 precipitate which is to be weighed. The precipitate is filtered and washed with 100 mL of distilled water. How -9 many moles of precipitate are dissolved in the washing? Ksp of Ba(I03)2 is 1.5 x 10 .

a. 1.5 x 10-9 mole b. 7.2 x 10-5 mole c. 1.1 X 10-4 mole d. 7.2 X 10-4 mole

30. After 3 millimoles of Pb(NO3)2 are dissolved in water, 4 millimoles of K2CrO4 are added making a total volume of 100 mL. What is the equilibrium concentration of Pb2+ in the -14 solution if Ksp for PbCrO4 is 2 x 10 .

a. 2 x 10-16 M b. 5 x 10-13 M c. 2 x 10-12 M d. 1.4 x 10-7 M

31. The percent transmittance (%T) and the absorbance (A) scales of a spectrophotometer span the ranges

a. %T = 1 → 100 A = oo → 0 b. %T = 0 → 100 A = 100 → 1 c. %T = 0 → 100 A = oo → 0 d. %T = 1 → 100 A = oo → 1

32. A sample of iron ore, weighing 0.700 gram, is dissolved in nitric acid. The solution is then diluted with water, following which sufficient concentrated aqueous ammonia is added to quantitatively precipitate the iron as Fe(OH)3. The precipitate is filtered, ignited, and finally weighed as Fe2O3. If the weight of the ignited and dried precipitate is 0.541 grams, what is the weight percentage of iron in the original ore sample? (AW for Fe = 55.85, AW for O = 16.00, AW for H = 1.01 g/mol)

a. 81.1% b. 54.1% c. 48.1% d. 27.0% 33. Measurement of the milliequivalents of calcium per liter of blood produced the following data: 4.15, 4.18, 4.25, 4.26; with a standard deviation of 0.05. If the t-value at the 95% probability level for three degrees of freedom (four measurements) is 3.18, what are the 95% confidence limits for the data?

a. 4.21  0.16 meq/L b. 4.21  0.08 meq/L c. 4.21  0.04 meq/L d. 4.18  0.04 meq/L

34. Precision can be expressed in absolute or relative terms. If the analyses of a sample for mercury content showed the following results (in mg Hg/liter): 0.5015, 0.5020, 0.5023, 0.5032; what would the relative average deviation from the mean, in parts per thousand (ppt) be? (Note: You can solve this problem without a standard deviation function on your calculator. Think about it!)

a. 0.1 ppt. b. 1.0 ppt. c. 1.4 ppt. d. 3.4 ppt.

35. Calculate the pH of the solution formed by adding 31.25 mL of 0.060 M NaOH to 25.0 -5 mL of a 0.075 M solution of acid HZ (Ka = 1.0 x 10 ).

a. 8.76 b. 10.76 c. 11.02 d. 3.24

36. The Student-t test may be used to compare mean values of two sets of data at a predetermined probability level. The name of this comparison test is the Null- Hypothesis. If the hypothesis fails the analyst can

a. look for determinate errors in one set of the data. b. identify the poor set of data and discard it. c. conclude that there is a difference in the mean value of the two sets of data at the level compared for each set. d. conclude both sets of data conform to the Normal Error Law. 37. Concentrated NH3 (aq) (NH4OH) solution is good for cleaning AgCl precipitates from crucibles because

+ a. the NH3 forms Ag(NH3) n complexes, increasing AgCl solubility. b. it reduces the AgCl to free Agº and Cl-, thus solubilizing the AgCl. + c. it oxidizes the AgCl to Ag and free Cl2, thus solubilizing the AgCl. d. AgCl is soluble in basic solution.

38. An excess of EDTA (ethylenediaminetetraacetic acid) must be added to Cr3+ solutions for quantitative reaction. A 123.0 mg sample containing chromium was dissolved and the chromium was then converted to Cr3+. 25.00 mL of 0.01000 M EDTA solution was added and allowed to react. The excess EDTA was titrated with 0.00950 M Zn2+ solution, requiring 10.00 mL. (AW for Cr = 52.00, FW for Cr2O3 = 152.0 g/mol)

The sample contained

a. 38.31% Cr203 b. 19.2% Cr203 c. 9.58% Cr203 d. 6.55% Cr203

39. A characteristic of EDTA (ethylenediaminetetraacetic acid) that is important for controlling the selectivity in complexation titrations is that

a. EDTA is highly colored. b. EDTA complexes alkali metal ions quantitatively. c. EDTA is a self-indicator. d. the conditional stabilities of EDTA’s complexes with metal ions are pH dependent.

40. For the titration of a metal (M) with EDTA (Y) using the metallochromic indicator (Ind), which of the following conditions must be satisfied in order to achieve an accurate end point?

a. M must not form complexes of appreciable stability with Ind. b. The complex M(ind) must have a moderately large formation constant, but a smaller formation constant than MY. c. The complex M(ind) must have a larger formation constant than the complex MY. d. The Ind must form a very stable complex with Y.

41. Which half reaction best corresponds to a saturated calomel electrode (SCE)?

a. AgCl + e-  Agº + Cl- b. Hg2+ + 2e-  Hgº - - c. HgCl2 + 2e  Hgº + 2Cl - - d. Hg2Cl2 + 2e  2Hgº + 2Cl 42. Given the half reactions below, calculate Ksp at 298 K for the solubility equilibrium of AgCl. (Hint: Add the equations together in such a way as to get the chemical reaction representing the solubility equilibrium. Log K = nEo/0.0592)

AgCl + e- ↔ Ag + Cl- Eº = 0.222 V Ag+ + e- ↔ Ag Eº = 0.800 V

a. 5.4 x 10-8 b. 3.0 x 10-20 c. 1.7 x 10-10 d. 5.8 x 109

43. For divalent cations in aqueous solution, a certain solid-state ion-selective electrode responds according to the following equation:

E = constant + 0.0591 x log[M2+]1/2

The potential of the electrode was determined to be 0.2500 V for a solution of Cu2+ with a concentration of 2.0 x 10-4 M. The potential of the electrode in an unknown solution of Cu2+ was 0.2796 V. What is the concentration of the Cu2+ in the unknown solution?

a. 6.3 x 10-3 M b. 2.0 x 10-3 M c. 6.3 x 10-4 M d. 2.0 x 10-4 M e. None of these is correct.

44. Given the reduction potentials in aqueous solution:

+ + - 2+ VO2 + 2H + e  VO + H2O E = 1.00 V (in 1 M acid) Fe3+ + e-  Fe2+ E = 0.771 V

Which pair of substances will react spontaneously?

a. VO2+ and Fe3+ + 2+ b. VO2 and Fe + 3+ c. VO2 and Fe d. VO2+ and Fe2+ 45. The iodometric method for the determination of copper (AW = 63.5 g/mol) is summarized by the reactions below:

2+ - - 2Cu + 5I  2CuI(s) + I3 - 2- 2- - I3 + 2S2O3  S4O6 + 3I

A 0.200 g sample of copper ore was analyzed according to the iodometric method with 32.5 mL of 0.100 M Na2S2O3 (MW = 158 g/mol) required to reach the starch end point. Which of the following correctly calculates the percent copper in the ore? (AW for Cu = 63.5, MW for Na2S2O3 = 158 g/mol)

2(0.100)(32.5)(63.5)(100) a. (0.200)(1000)

215(0.100)(32.5)(63.5)(100) b. (0.200)(1000)

(0.100)(32.5)(63.5)(100) c. (0.200)(158)(1000)

(0.100)(32.5)(63.5)(100) d. (0.200)(1000)

46. A sample of potassium nitrate and inert materials weighing 1.500 grams is dissolved in 75.00 mL of water. A 15.00 mL aliquot of this solution is passed through a cation exchange resin (hydrogen form) column. Note that the K+ replaces the H+ on the resin. The effluent requires 12.00 mL of 0.1010 M sodium hydroxide for neutralization. The percentage of potassium nitrate, KNO3 (MW = 101.1 g/mol) in the sample is

a. 8.16% b. 10.2% c. 15.0% d. 40.8%

47. When a molecular substance in a solid or solution exhibits fluorescence, the light emitted is of

a. the same intensity as that absorbed. b. a shorter wavelength than that absorbed. c. a higher energy than that absorbed. d. a longer wavelength than that absorbed. 48. It is generally inadvisable to make a spectrophotometric measurement of an absorbance at a wavelength where the molar absorptivity changes rapidly with wavelength because of several reasons. One of the reasons is that

a. narrow spectral bandwidths are required from an instrument to avoid deviations from Beer’s Law behavior. b. the sample can generate fluorescence more efficiently so that the absorption measurement becomes erroneous. c. the sample will decompose more readily when one is exciting on the edge of an excited state energy surface. d. one is exciting into states that have poor Frank-Condon overlap factors with the ground state wave functions.

49. Compound A exhibits a molar absorptivity of 10,000 at 430 nm and 5000 at 500 nm while compound B has a molar absorptivity of 1000 at 430 nm and does not absorb at 500 nm. Calculate the concentration of A and B present in a solution having an absorbance in a 1.0 cm cell of 0.72 at 430 nm and of 0.30 at 500 nm.

a. A = 7.2 x 10-5 M; B = 7.2 x 10-4 M b. A = 6 x 10-5 M; B = 1.2 x 10-4 M c. A = 6 x 10-5 M; B = 7.2 x 10-4 M d. A = 6 x 10-4 M; B = 7.2 x 10-4 M e. None of these is correct. 50. Consider the spectrophotometric titration of, A + T → P, where A is the analyte and T is the titrant. If both T and A, but not P, absorb at the wavelength at which the absorbance is measured which of the following titration curves would result?

Volume T

Volume T c.

Volume T

Volume T 51. Which operation would double the absorbance of an absorbing sample?

a. Decreasing the path length by a factor of log 2. b. Increasing the solute concentration by a factor of log 2. c. Increasing the path length by a factor of 2. d. Decreasing the solute concentration by a factor of 2.

52. A certain spectrophotometer is capable of detecting an absorbance of 0.001. If a trace analysis of a compound with a molar absorptivity of 1 x 105 is desired and a 1.0 cm path length cell will be used, what is the lowest concentration that can be detected with this instrument?

a. 102 M b. 10-2 M c. 10-6 M d. 10-8 M

53. What is the pH of the solution that results when 45.0 mL of 0.100 M NaOH(aq) are mixed with 50.0 mL of 0.100 M HNO3(aq).

a. 2.28 b. 2.97 c. 0.30 d. 1.00

54. Calculate the cell potential, Ecell, for a voltaic cell that utilizes the reaction below at 25C 3+ -7 2+ when [Sc ] = 6.3 x 10 M and [Cu ] = 1.2 M. The standard potential, Ecell, for the cell is 2.42 V.

3Cu2+(aq) + 2Sc(s)  3Cu(s) + 2Sc3+(aq)

a. 2.54 V b. 3.18 V c. 2.30 V d. 2.18 V

55. Which of the following compounds is the most soluble in water?

-27 a. CdS, Ksp = 8.0 x 10 -28 b. PbS, Ksp = 8.0 x 10 -36 c. CuS, Ksp = 6.3 x 10 -10 d. BaSO4, Ksp = 1.1 x 10 -5 56. The acid 4-aminobenzoic acid, HB, has Ka = 1.2 x 10 . The pH of a 0.23 M solution of HB in water is approximately:

a. 3.20 b. 2.78 c. 4.92 d. 5.56

57. Which of the statements below about the following redox reaction is correct?

- + 2+ 3Co(s) + 2NO3 (aq) + 8H (aq)  2NO(g) + 3Co (aq) + 4H2O(l)

- a. Co is the oxidizing agent and NO3 is the reducing agent. - b. Co is the reducing agent and NO3 is the oxidizing agent. c. Co is the reducing agent and H+ is the oxidizing agent. + - d. H is the reducing agent and NO3 is the oxidizing agent.

58. The glass electrode is used for the potentiometric measurement of

a. Cu2+ ion concentration. b. pH. c. Na+ ion concentration. d. Fe3+ ion concentration.

59. What is the approximate pH for a saturated solution of Mg(OH)2? The Ksp for Mg(OH)2 = 5.6 x 10-12.

a. 10.35 b. 10.87 c. 9.84 d. 10.04

60. Calculate the absorbance for an analyte solution that has a percent transmittance of 42.4 %.

a. 0.372 b. 1.627 c. 0.00424 d. 0.422

61. Which of the following is a Bronsted-Lowry conjugate acid-base pair?

+ - a. H3O /OH 2- b. H3PO4/HPO4 - c. CH3COOH/CH3COO 2- d. H2SO4/SO4 62. In a gravimetric precipitration, digestion is used to

a. generate the precipitating agent slowly. b. prevent certain impurities from reacting with the precipitant. c. change the chemical form of the precipitate. d. increase particle size and expel impurities from precipitate crystals. e. pass the time after eating a candy bar for a snack.

63. A 315.0 mg sample of impure calcium carbonate, CaCO3 (FW = 100.1 g/mol), was analyzed by addition of 50.00 mL of 0.1120 M HCl. The excess unreacted HCl was then backtitrated with 11.05 mL of 0.05513 M NaOH. Calculate the percent CaCO3 in the sample.

a. 26.8 % b. 79.3 % c. 55.2 % d. 85.8 %

-9 64. Calculate the molar solubility of Ba(IO3)2 in water if Ksp = 1.57 x 10 .

a. 1.57 x 10-9 M b. 7.32 x 10-4 M c. 3.96 x 10-5 M d. 1.98 x 10-5 M

65. Which of the following methods is best suited for determining trace amounts (ppm levels) of iron in a sample of well water?

a. infrared spectroscopy b. titration with NaOH c. precipitation with NH3 d. atomic absorption

66. Calculate the pCl for a solution prepared by mixing 50.0 mL of 0.050 M NaCl and 75.0 mL of 0.050 M BaCl2.

a. 1.60 b. 1.10 c. 1.30 d. 1.80 67. According to Beer’s law, the absorbances from all species in a sample solution that absorb at the same wavelength are

a. averaged to give an average absorbance. b. subtracted to give a net absorbance. c. added to give a total absorbance. d. subtracted to give the apparent absorbance.

68. How many electrons are transferred in the overall redox reaction below?

2- + 2+ 3+ 3Ni(s) + Cr2O7 + 14H  3Ni + 2Cr (aq) + 7H2O(l) a. 2 b. 12 c. 6 d. 8

69. Calculate the cell potential, Ecell, for the galvanic cell that utilizes the reaction below when [Cr3+] = 0.10 M and [Ag+] = 0.00020 M. (E for Cr3+(aq) + 3e-  Cr(s) is –0.74 V; E for Ag+ + e-  Ag(s) is 0.80 V.)

Cr(s) + 3Ag+(aq)  3Ag(s) + Cr3+(aq)

a. 1.41 V b. 1.54 V c. 0.26 V d. None of these is correct

70. A solution of K4Fe(CN)6 (FW = 368.347 g/mol), was prepared by dissolving 0.02278 g of the solid into enough water to give a solution volume of 1.200 x 103 mL. Calculate the ppm of K+ (AW = 39.0983 g/mol) in the solution.

a. 19.0 ppm b. 76.0 ppm c. 8.06 ppm d. 32.4 ppm

71. Calculate the concentration of a solution prepared by diluting 50.0 mL of 0.200 M HCl to a total volume of 375.0 mL.

a. 0.0267 M b. 0.0235 M c. 1.50 M d. 0.0312 M 72. Titration of 35.00 mL of 0.06251 M Na2C2O4 (FW = 134.00 g/mol) required 43.63 mL of KMnO4 (FW = 158.03) solution. Calculate the molarity of the KMnO4 solution.

2- - + 2+ 5C2O4 + 2MnO4 + 16H  10CO2 + 2Mn + 8H2O

a. 0.02006 M b. 0.01550 M c. 0.03224 M d. 0.02621 M

73. One advantage of the single-beam spectrophotometer compared to the double-beam spectrophotometer is that

a. it compensates for drift in the source intensity. b. it compensates for the drift in detector response. c. it is significantly less expensive. d. it covers a wider range of wavelengths.

74. Calculate the equilibrium constant for the redox reaction below, given that E for Ag+ + e-  Ag = 0.80 V, and E for Ni2+ + 2e-  Ni = -0.23 V.

Ni(s) + 2Ag+(aq)  Ni2+(aq) + 2Ag(s) a. 11 b. 5.4 x 1024 c. 1.2 x 1019 d. 6.6 x 1034

75. What is the correct shorthand notation for the voltaic cell that utilizes the reaction below. Fe(s) + Cu2+(aq)  Fe2+(aq) + Cu(s)

a. Fe(s)/Fe2+(aq)//Cu2+(aq)/Cu(s) b. Cu(s)/Cu2+(aq)//Fe2+(aq)/Fe(s) c. Fe(s)/Cu2+(aq)//Fe2+(aq)/Cu(s) d. Pt(s)/Fe2+(aq)//Cu2+(aq)/Pt(s)

76. Calculate the pH at the point in the titration at which 13.0 mL of 0.0980 M NaOH has -4 been added to 25.0 mL of a 0.121 M solution of diprotic acid H2M (Ka1 = 1.3 x 10 , Ka2 = 2.5 x 10-7).

a. 4.02 b. 3.75 c. 4.77 d. 2.61 77. The following Beer’s law plot (calibration curve) was obtained for a series of standards containing the analyte R. The absorbance of an unknown test solution of the analyte was found to be 0.763. The test solution was prepared by diluting the original sample solution by a factor of 50 to form a second solution which was diluted by a factor of 15 to prepare the test solution. Calculate the concentration of the analyte in the original sample solution.

1.4 y = 1.128x + 0.07 1.2

n 0.8 a b r o

s 0.6 b A

0 0.00 0.20 0.40 0.60 0.80 1.00 1.20 ppm

a. 461 ppm b. 355 ppm c. 30.7 ppm d. 507 ppm

78. How many significant figures are contained in the following measurement: 0.005160 g?

a. 6 b. 2 c. 4 d. 3 e. 7

79. The pH for an amphiprotic salt derived from a diprotic acid may be calculated using which of the following equations?

a. pH = -log[(Ka1 + Ka2)/2] b. pH = pKa1/2 c. pH = (pKa1 + pKa2)/2 d. pH = -log(Ka1 + Ka2) e. pH = (pKa1 – pKa2)/2 80. A primary standard solution of silver nitrate solution is made by dissolving 12.25 g of solid AgNO3 (FW = 169.87 g/mol) into 1.00 L solution. How many mL of this solution will react with 0.1197 g BaCl2.2H2O (FW = 244.263 g/mol)?

a. 13.6 b. 6.80 c. 3.40 d. 27.2

81. Calculate the concentration of Co2+ in a solution that is prepared by mixing 1.50 millimoles Co2+ and 2.50 millimoles EDTA into 1000 mL of solution that has been 2- 16 -11 buffered to a pH of 3.0. (Kf for CoY = 2.0 x 10 , α4 = 3.30 x 10 )

a. 7.5 x 10-17 M b. 2.3 x 10-6 M c. 0.0015 M d. 4.1 x 10-9 M

82. Which of the following is most likely to affect the volume of water measured from a glass volumetric buret?

a. change in the volume of glass with temperature b. refractive index of water c. conductivity of the aqueous solution d. change in the volume of water with temperature

83. In reverse-phase chromatography, the stationary phase is nonpolar and the mobile phase is polar. As a result, the most polar compound in a sample comes off of the column first because it is the most soluble compound in the mobile phase, and the least polar compound comes off last. Based on this, which of the following compounds would come off of the column last in a reverse-phase separation, assuming all four compounds were present in a sample?

a. C4H9COOH b. C5H12 c. C2H5COC2H5 d. C2H5CHOHC2H5

84. The Q-test provides a means for deciding if an outlier can be rejected or should be retained in a set of data. When the Q-test indicates that a suspected outlier can be rejected with a certain degree of confidence, the implication is that

a. there is a significant random error present. b. there could be an undetected gross error. c. the standard used for rejection was too strict and the Q-test needs to be applied again with a new degree of confidence. d. the experiment should be repeated. Key

Question # Answer Question # Answer 1 D 43 B 2 B 44 B 3 C 45 D 4 C 46 D 5 A 47 D 6 C 48 A 7 A 49 B 8 D 50 B 9 B 51 C 10 A 52 D 11 B 53 A 12 B 54 A 13 B 55 D 14 D 56 B 15 C 57 B 16 A 58 B 17 C 59 A 18 C 60 A 19 C 61 C 20 A 62 D 21 D 63 B 22 B 64 B 23 C 65 D 24 B 66 B 25 C 67 C 26 C 68 C 27 B 69 D 28 C 70 C 29 B 71 A 30 C 72 A 31 C 73 C 32 B 74 D 33 B 75 A 34 B 76 B 35 A 77 A 36 C 78 C 37 A 79 C 38 C 80 A 39 D 81 B 40 B 82 D 41 D 83 A 42 C 84 B