CHE 226 ANALYTICAL CHEMISTRY Spring 2005

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1 CHE 226 ANALYTICAL CHEMISTRY FINAL EXAM May 5, 2005 Name WRITE YOUR NAME ON EACH EXAM PAGE NOW. THERE ARE 10 QUESTIONS WORTH 155 POINTS TOTAL ON THIS EXAM. Show clearly all work on these pages. Use the proper number of significant figures and the correct units in all final answers. You must show your calculations and/or reasoning, including equations, on a question to obtain any credit; no credit for answers appearing out of the blue. Your work must be understandable at the time it is being graded to obtain any partial credit. Very little will be subtracted for routine arithmetic errors, but all numerical answers must be shown to the proper number of significant figures. Programmable calculators as well as a single 8.5 by 11 cheat sheet are allowed, but may not be shared with anyone else. Tables of data and other information that may be useful are appended to the back of the exam. Use the backs of the pages as scrap paper. Anything written on the backs of pages is totally irrelevant to the grading process. Unless otherwise stated, assume all solutions are aqueous, density = g/ml; activity coefficients are unity (i.e., activity = concentration); temperature, T = 298 K; K w = x QUESTION 1 /10 QUESTION 7 /32 QUESTION 2 /10 QUESTION 8 /20 QUESTION 3 /28 QUESTION 9 / 8 QUESTION 4 /10 QUESTION 10 /11 QUESTION 5 /12 QUESTION 6 /14 TOTAL /155

2 1. (10 points) Cyanate ion in waste solutions from gold mining operations can be destroyed by treatment with hypochlorite ion in basic solution. Write a balanced oxidation-reduction equation for this reaction: OCN -1 (aq) + OCl -1-2 (aq) CO 3 (aq) + N 2(g) + Cl -1 (aq) 2. (10 points) For the following electrochemical reaction: - 2 IO 3 (aq) + 5 SO 2(g) + 4 H 2 O (l) 8 H + -2 (aq) + 5 SO 4 (aq) + 1 I 2(s) a) (5 points) Calculate E o cell. Is this reaction spontaneous? b) (3 points) Calculate G o. c) (2 points) What type of electrochemical cell is this? CHE 226 FINAL EXAM 2

3 3. (28 points) A house is tested for radon once in the summer and again in the winter. The results, reported as parts per million of radon, are tabulated below. Sample # Summer (ppm) Winter (ppm) Sum Mean a) (2 points) What is the median winter measurement? b) (5 points) Calculate the standard deviation for the winter measurements. c) (3 points) Calculate the standard error of the mean for the winter measurements. d) (8 points) If it is assumed that radon is typically stays fairly evenly distributed throughout a house, can any of the summer measurements be rejected as an outlier at the 90% confidence level? At the 95% confidence level? CHE 226 FINAL EXAM 3

4 e) (3 points) When one moves from a confidence level of 90% to one of 95%, what does this do to the size of the confidence interval? f) (7 points) If s pooled is ±0.06 ppm, is there a statistically significant difference in the two means at the 99 % confidence level? 4. (10 points) Find the solubility of silver arsenate (Ag 3 AsO 4(s), K sp = 6.0 x ) ignoring any complex equilibria that might arise from dissolution of the solid or autoprotolysis of water in: a) (6 points) Pure water. b) (4 points) M AgNO 3. CHE 226 FINAL EXAM 4

5 5. (12 points) A ml portion of M Ca(NO 3 ) 2 (aq) is added to ml of M Na 2 CO 3(aq), forming CaCO 3(s) with a K sp of 4.5 x Ignoring any acid-base equilibria that might arise from carbonate reacting with water and from water s autoprotolysis, a) (8 points) Find the Ca +2 concentration of the resulting solution, in moles/liter. b) (4 points) Express the Ca +2 concentration in parts per billion. (Helpful molar masses to consider: C g/mol, N g/mol, O g/mol, Na g/mol, Ca g/mol) 6. (14 points) If 3.00 grams of Ce(ClO 3 ) 4 (molar mass = g/mol) are dissolved in ml of deionized water, a) (8 points) Calculate the ionic strength of the resulting solution. b) (6 points) Calculate the activity coefficient for Ce +4 (γ cerium ) using the extended Debye-Huckel equation. What does this tell you about the cerium ion? CHE 226 FINAL EXAM 5

6 7. (32 points) Find the ph of the following: a) (8 points) 4.50 x 10-9 M Sr(OH) 2, a strong electrolyte b) (8 points) 175 ml of M KNO 3 mixed with 225 ml M HNO 3 c) (8 points) mol benzoic acid ( HBenz, K a = 6.28 x 10-5 ) and mol potassium benzoate ( KBenz ) diluted to 2.00 L. d) (8 points) A 5.00 x 10-5 M solution of sodium dihydrogen citrate ( NaH 2 Cit ). For citric acid, K a1 = 7.45 x 10-4, K a2 = 1.73 x 10-5, K a3 = 4.02 x CHE 226 FINAL EXAM 6

7 8. (20 points) For the following questions, consider a 1.00 x 10-3 M solution of formic acid (HCOOH, K a = 1.80 x 10-4 ), a weak monoprotic acid. a) (6 points) Write all of the relevant equilibrium expressions with their associated equilibrium K expressions. b) (6 points) Write all of the relevant mass and charge balance expressions for the system. Include actual numeric values where possible. c) (8 points) What is the ph of the system at equilibrium? 9. (8 points) Nickel (II) can complex up to six ammonia molecules as ligands. The β i values are , , , , , for i = 1-6. a) (4 points) Write out the equilibrium expression for β 4. b) (4 points) What is the value of K f4? CHE 226 FINAL EXAM 7

8 10. (11 points) Boric acid (H 3 BO 4 ) has the following values for acid dissociation constants at 25 o C: K a1 = , K a2 = , and K a3 = a) (5 points) Write out the expression for the α 3 term. b) (3 points) What is the value of the α 3 term when the ph is 4.000? c) (3 points) What specifically does the value of α 3 tell you about the system when the ph is 4.000? CHE 226 FINAL EXAM 8

9 Confidence Levels for Various Values of z Confidence Levels, % Z Values of t for Various Levels of Probability Degrees of Factor for Confidence Interval Freedom 80% 90% 95% 99% 99.9% CHE 226 FINAL EXAM 9

10 Critical Values for the Rejection Quotient, Q Number of Observations 90% Confidence 95% Confidence 99% Confidence Q crit Ion-size parameters in Angstroms (10-10 m) 11: Ce 4+, Sn 4+, Th 4+, Zr 4+ 9: Al 3+, Cr 3+, Eu 3+, Fe 3+, H +, In 3+, La 3+, Sc 3+, Y 3+, 8: Be 2+, Mg 2+ 6: Ca 2+, Co 2+, Cu 2+, Li +, Mn 2+, Ni 2+, Zn 2+ 5: Ba 2+, Cd 2+, Hg 2+, Ra 2+, Sr 2+, S 2-4.5: CH 3 COO, Pb 2+, CO 2 3, SO 2 3, MoO 2 4, S 2 O 2 2 3, HPO 4 4: Na +, IO 3, HSO 3, SO 2 3 4, PO 4 3.5: OH, F SCN, OCN, SH ; ClO 3, ClO 4, BrO 3 ; IO 4 3: CN, K +, Cl ; Br, I ; NO 2, NO 3 2.5: Ag +, Cs +, NH + 4, Rb +, Tl + Selected Standard Electrode Potentials at 25 o C Reduction Half-Reaction E o, Volts F 2(g) + 2 e - 2 F -1 (aq) S 2 O 8 (aq) + 2 e - O 2(g) + H 2 O (l) H 2 O 2(aq) + 2 H + (aq) + 2 e - 2 H 2 O (l) Cr 2 O 7 (aq) + 14 H + (aq) + 6 e - 2 Cr +3 (aq) + 7 H 2 O (l) IO 3 (aq) + 12 H + (aq) + 10 e - 1 I 2(s) + 6 H 2 O (l) I 2(s) + 2 e - 2 I -1 (aq) SO 4 (aq) + 4 H + (aq) + 2 e - 2 H 2 O (l) + 1 SO 2(g) S(s) + 2 H + (aq) + 2 e - H 2 S (g) H + (aq) + 2 e - H 2(g) 0 Co +2 (aq) + 2 e - Co (s) H 2 O (l) + 2 e - H 2(g) + 2 OH -1 (aq) Li + (aq) + e Li (s) CHE 226 FINAL EXAM 10

11 SELECTED CONSTANTS, UNITS, AND CONVERSION FACTORS [The uncertainty in the last digit(s) is shown italicized in parentheses] Atomic mass constant: m u = x kg Avogadro s number: N = (47) x mol -1 Boltzmann constant: k = (24) x J/K Elementary charge: e = (63) x C Faraday constant: F = (39) C/mol Molar gas constant: R = (15) J/K-mol = cal/k-mol = L-atm/K-mol = m 3 /mol at STP Pi: π = Planck s constant: h = (52) x J-s Speed of light (in a vacuum): c = (exact) x 10 8 m/s Stefan-Boltzmann constant: σ = (40) x 10-8 W/m 2 -K 4 Standard acceleration of gravity: g n = (exact) m/s 2 Wein constant: k = (51) x 10-3 m-k Force: 1 N = 1 kg-m/s 2 Joule: 1 J = 1 N-m = 1 kg-m 2 /s 2 = 10 7 ergs = 1 V x 1 C = 1 V-C = (J/C)(C) Power: 1 W = 1 J/s = 1 V x 1 A = 1 V-A = (J/C)(C/s) Electron Volt: 1 ev = (63) x J = x cal Calorie (thermochemical): 1 cal = J [Food calorie = 1 Cal = 1000 cal] Length: 1 km = 1000 m = mi 1 in = 2.54 cm (exactly) Mass: 1 kg = 1000 g 1 pound = g Pressure: (exact) Pa = 1 atm = 760 mm Hg = lb/in Pa = 1 torr = 1 mm Hg 10 5 Pa = 1 bar 1 Pa = 1 N/m 2 Volume: 1 L = 10-3 m 3 = 1000 ml = 1000 cm 3 = quarts Nernst factor: (RT/nF) ln = ( V/n) log 10 at 25 o C nf/rt = n V -1 RT/nF = /n V G o = -nfe o = -RT(ln K eq ) G = -nfe = -RT(ln Q) µ = x + zσ/n 1/2 µ = x + ts/n 1/2 Ion Product for Water pk w = at 15 o C, at 25 o C, at 40 o C Some Less Common Multiplicative Prefixes: P = peta = T = tera = G = giga = 10 9 n = nano = 10-9 p = pico = f = femto = a = atto = z = zepto = y = yocto = [See for additional information.] CHE 226 FINAL EXAM 11

CHE 226 ANALYTICAL CHEMISTRY Spring 2005

CHE 226 ANALYTICAL CHEMISTRY Spring 2005 CHE 226 ANALYTICAL CHEMISTRY EXAM II March 10, 2005 Name WRITE YOUR NAME ON EACH EXAM PAGE NOW. THERE ARE 10 QUESTIONS AND 109 POINTS TOTAL IN THIS EXAM. Show clearly all work on these pages. Use the proper