UK CHE 226 - CHE 226 Final Exam
Course Che 226-
Pages 10

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CHE 226 ANALYTICAL CHEMISTRY Fall 2004 FINAL EXAM – December 14, 2004 Name ______________________________ WRITE YOUR NAME ON EACH EXAM PAGE NOW. THERE ARE 11 QUESTIONS AND 145 POINTS TOTAL IN THIS EXAM. FINAL % SCORE = # POINTS/135. 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. You do not have to do the final arithmetic on a question unless you need to have a numerical value for the next part of a question or for a statistical test, as long as the answer is expressed in its final form and all algebraic manipulations have been made. 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 must have all memory erased. A calculator may be used, but not 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 will be ignored unless you add an explanatory note on the front of the page. 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 ___________ /20 QUESTION 7 ___________ /5 QUESTION 2 ___________ /10 QUESTION 8 ___________ /10 QUESTION 3 ___________ /10 QUESTION 9 ___________ /15 QUESTION 4 ___________ /10 QUESTION 10 __________ /10 QUESTION 5 ___________ /30 QUESTION 11 __________ /10 QUESTION 6 ___________ /15 TOTAL __________ /145Name __________________________________ 1. (20 Points) Tripolyphosphoric acid, H5P3O10 was a common ingredient in high-phosphate detergents as its penta-sodium salt. It was relatively cheap, would make the washing solution quite basic, and was also a good complexing agent for sequestering ions in the tap water used and those extracted from the soiled clothes. It has largely been replaced in modern detergents because of concerns about excessive phosphate pollution of natural waters. For simplicity, designate the fully protonated acid as H5TPP. The acid’s five pKa’s are listed as ~1, ~2, 2.79, 6.47, and 9.24, respectively. (a) (10 Points) What would be the predominant chemical form of H5TPP in natural waters, assuming the pH = 7.00? What fraction of the total TPP-containing forms present would this form constitute? [Remember, you do not need to do the final arithmetic.] (b) (10 Points) It was stated that the penta-sodium salt of TPP makes a clothes-washing solution quite basic. Assume that you have a 0.50 M solution of Na5TPP. Calculate the pH of that solution. CHE 226 Final Exam Fall 2004 2Name __________________________________ 2. (10 Points) Write the mass-balance equations for a solution that is saturated in calcium phosphate Ca3(PO4)2 and also contains 0.050 M CaCl2. Let the molar solubility be represented by S. Assume no complexation of the calcium ion takes place. 3. (10 Points) Write the charge-balance equation for a solution that is 0.05 M in lead dibromide, PbBr2. The lead ion can complex up to two bromide ions to form soluble complexes. 4. (10 Points) Auric chloride, AuCl3, is relatively insoluble, Ksp = 3.2 x 10-25. Calculate the theoretical solubility, S, of auric chloride. Assume that no hydrolysis or complexation reactions occur. CHE 226 Final Exam Fall 2004 3Name __________________________________ 5. (30 Points) Manufacturers of blood-glucose meters routinely test large lots of the “test strips” used in their meters with standard glucose solutions for quality-control purposes. The analysis report included in one lot of the test strips for an Accu-Chek CompactTM glucometer is shown in the small table below. Answer the questions posed. [I believe that the actual unit involved is the clinically common, but weird, unit of mg/dL.] Control Range Mean Low 35-65 50 High 323-437 380 (a) (5 Points) Assume that the “Range” indicated for the Low and High glucose Control standards represent ± 3σ for a rather large number of replicate measurements on this lot of test strips. What fraction (or %) of all measurements should fall within the assumed Range of ± 3σ around the Mean. (b) (15 Points) Let the general term “error” in this problem mean plus or minus one standard deviation, ± s or ± σ. Calculate both the relative (± erel) and the absolute (± eabs) errors for both the “Low” and the “High” standard solutions. [Hint: Construct a 2 x 2 table showing your calculations and the resultant values.] (c) (10 Points) Consider your results from (b). If someone asked you, what is the single, “best estimate” of the “error” in a blood-glucose measurement over the entire measurement range of 50-380, what would you say? Why? You’ve got to give them one simple value: “It’s about plus and minus ...” CHE 226 Final Exam Fall 2004 4Name __________________________________ 6. (15 Points) Ferric ion can be complexed by up to three chloride ions to form soluble complexes. The values of the stepwise formational constants, Kf’s, are equal to 30, 135 and 98, respectively. (a) (5 Points) Calculate the value of the overall formational constant, which would be denoted as β3, for the reaction Fe3+ + 3 Cl- ' FeCl3 (aq) (b) (10 Points) You wish to do a quick-and-dirty, back-of-the-envelope calculation on the possible absorption of ferric ion in the stomach. Stomach acid is about 0.1 M HCl. If you add a “small” amount of ferric ion (say about 10-4 M) to 0.1 M HCl, what fraction of the iron added remains in the form of free, uncomplexed Fe3+? To simplify the situation for a very crude estimate, ignore the first two stepwise formational constants and do the calculation using only the β3. [Note: Two additional simplifying assumptions will greatly


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UK CHE 226 - CHE 226 Final Exam

Course: Che 226-
Pages: 10
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