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UK CHE 226 - ANALYTICAL CHEMISTRY FINAL EXAM
Course Che 226-
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CHE 226 ANALYTICAL CHEMISTRY Spring 2005 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 = 1.0000 g/mL; activity coefficients are unity (i.e., activity = concentration); temperature, T = 298 K; Kw = 1.008 x 10-14. 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 __________ /155Name __________________________________ 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(aq) CO3-2(aq) + N2(g) + Cl-1(aq) → 2. (10 points) For the following electrochemical reaction: 2 IO3-(aq) + 5 SO2(g) + 4 H2O(l) 8 H+(aq) + 5 SO4-2(aq) + 1 I2(s) → a) (5 points) Calculate Eocell. Is this reaction spontaneous? b) (3 points) Calculate ∆Go. c) (2 points) What type of electrochemical cell is this? CHE 226 FINAL EXAM Spring 2005 2Name __________________________________ 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) 1 0.26 0.37 2 0.27 0.48 3 0.17 0.33 4 0.30 0.50 5 0.28 0.42 Sum 1.28 2.10 Mean 0.26 0.42 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 Spring 2005 3Name __________________________________ 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 spooled 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 (Ag3AsO4(s), Ksp = 6.0 x 10-23) 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) 0.0200 M AgNO3. CHE 226 FINAL EXAM Spring 2005 4Name __________________________________ 5. (12 points) A 150.0 ml portion of 0.0300 M Ca(NO3)2(aq) is added to 100.0 ml of 0.0150 M Na2CO3(aq), forming CaCO3(s) with a Ksp of 4.5 x 10-9. 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 12.011 g/mol, N 14.007 g/mol, O 15.999 g/mol, Na 22.990 g/mol, Ca 40.078 g/mol) 6. (14 points) If 3.00 grams of Ce(ClO3)4 (molar mass = 473.9186 g/mol) are dissolved in 500.0 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 (γcerium) using the extended Debye-Huckel equation. What does this tell you about the cerium ion? CHE 226 FINAL EXAM Spring 2005 5Name __________________________________ 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 0.225 M KNO3 mixed with 225 ml 0.175 M HNO3 c) (8 points) 0.0495 mol benzoic acid (“HBenz,” Ka = 6.28 x 10-5) and 0.0335 mol potassium benzoate (“KBenz”) diluted to 2.00 L. d) (8 points) A 5.00 x 10-5 M solution of sodium dihydrogen citrate (“NaH2Cit”). For citric acid, Ka1 = 7.45 x 10-4, Ka2 = 1.73 x 10-5, Ka3 = 4.02 x 10-7. CHE 226 FINAL EXAM Spring 2005 6Name __________________________________ 8. (20 points) For the following questions, consider a 1.00 x 10-3 M solution of formic acid (HCOOH, Ka = 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 βi values are 10-2.80, 10-5.04, 10-6.77, 10-7.96, 10-8.71, 10-8.74 for i = 1-6. a) (4 points) Write out the equilibrium expression for β4. b) (4 points) What is the value of Kf4? CHE 226 FINAL EXAM Spring 2005 7Name __________________________________ 10. (11 points) Boric acid (H3BO4) has the following values for acid dissociation constants at 25oC: Ka1 = 10-9.24, Ka2 = 10-12.74, and Ka3 = 10-13.80. a) (5 points) Write out the expression


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UK CHE 226 - ANALYTICAL CHEMISTRY FINAL EXAM

Course: Che 226-
Pages: 11
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