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UK CHE 226 - ANALYTICAL CHEMISTRY EXAM II
Course Che 226-
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CHE 226 ANALYTICAL CHEMISTRY Fall 2005 EXAM II – October 27, 2005 Name ______________________________ WRITE YOUR NAME ON EACH EXAM PAGE NOW. THERE ARE 7 QUESTIONS AND 104 PERCENT TOTAL IN 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. 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, 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 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 ___________ / 24 Question 7 ___________ /12 QUESTION 2 ___________ /10 Question 8 ___________ / QUESTION 3 ___________ /12 Question 9 ___________ / QUESTION 4 ___________ /5 Question 10 ___________ / QUESTION 5 ___________ /12 Question 11 ___________ / QUESTION 6 ___________ /29 TOTAL ___________ /104Name __________________________________ CHE 226 Exam II Fall 2005 21. (24 Points) You wish to calculate the solubility (S) of silver phosphate, Ag3PO4, taking into account all possible reactions. Silver phosphate is relatively insoluble, it has a Ksp. The hydrogen phosphate ion is one of the acid-base forms originating from phosphoric acid, H3PO4, which has three acid dissociation constants. Designate them as Ka1, Ka2, and Ka3. (a) (10 Points) Write out all the relevant chemical equilibrium reactions for this system, along with the appropriate equilibrium constant for each equation. (b) (9 Points) Write the mass-balance equation(s) for this system (c) (5 Points) Write the charge-balance equation for this system.Name __________________________________ CHE 226 Exam II Fall 2005 32. (10 points) The experimental molar solubility, S, of Ag3PO4 in water is 4.8 x 10-5 M. Calculate the numerical value for the Ksp of silver phosphate. Assume that no hydrolysis or complexation of the dissolved ions occurs. 3. (12 Points) Calculate the solubility, S, of PbI2 in 0.10 M NaI if the Ksp for lead iodide is 7.1 x 10−9. 4. (5 points) The ferric ion, Fe3+, can be complexed by up to three chloride ions to form soluble complexes. The three stepwise formational constants have been measured to be Kf1 = 30, Kf2 = 135, and Kf3 = 98. Calculate the value for the overall formational constant, β3, for the reaction Fe3+ + 3 Cl− ' FeCl3 (aq)Name __________________________________ CHE 226 Exam II Fall 2005 45. (12 Points) Calculate the ionic strength of a solution that is 0.030 M in Rb2SO4. 6. (29 Points) Calculate the pH of the following aqueous solutions. (a) (5 Points) 0.0010 M HCl (b) (12 Points) Saturated Pb(OH)2. Ksp = 1.2 x 10−15. (c) (12 Points) 0.075 M sodium hypochlorite, NaOCl. The Ka for hypochlorous acid is 3.0 x 10−8.Name __________________________________ CHE 226 Exam II Fall 2005 57. (12 Points) In order to evaluate a spectrophotometric method for the determination of titanium, the method was applied to a certified alloy sample that contained 0.496 % Ti by mass. The average and standard deviation for 8 replicate analyses were 0.482 ± 0.0257 % by mass. Does the mean differ significantly from the certified value at the 95% confidence level?Name __________________________________ CHE 226 Exam II Fall 2005 6Confidence Levels for Various Values of z Confidence Level, % z [ z = (x – µ)/σ ] 50 0.675 68.3 1.000 80.0 1.282 90 1.645 95 1.960 95.4 2.000 99 2.576 99.7 3.000 99.9 3.291 Values of t for Various Levels of Probability – Two-Tailed Test (±) Degrees of Factors for the Confidence Interval Freedom, ν 80% 90% 95% 99% 99.9%_ 1 3.08 6.31 12.7 63.7 637 2 1.89 2.92 4.30 9.92 31.6 3 1.64 2.35 3.18 5.84 12.9 4 1.53 2.13 2.78 4.60 8.60 5 1.48 2.02 2.57 4.03 6.86 6 1.44 1.94 2.45 3.71 5.96 7 1.42 1.90 2.36 3.50 5.40 8 1.40 1.86 2.31 3.36 5.04 9 1.38 1.83 2.26 3.25 4.78 10 1.37 1.81 2.23 3.17 4.59 11 1.36 1.80 2.20 3.11 4.44 12 1.36 1.78 2.18 3.06 4.32 13 1.35 1.77 2.16 3.01 4.22 14 1.34 1.76 2.14 2.98 4.14 15 1.34 1.75 2.13 2.95 4.07 20 1.32 1.72 2.09 2.84 3.85 25 1.32 1.71 2.06 2.79 3.72 30 1.31 1.70 2.04 2.75 3.65 40 1.30 1.68 2.02 2.70 3.55 ∞ 1.282 1.645 1.960 2.576 3.291 Number of Qcrit (Reject if Qcalc > Qcrit) Observations, n 90% C.L. 95% C.L. 99% C.L. 3 0.941 0.970 0.994 4 0.765 0.829 0.926 5 0.642 0.710 0.821 6 0.560 0.625 0.740 7 0.507 0.568 0.680 8 0.468 0.526 0.634 9 0.437 0.493 0.598 10 0.412 0.466 0.568Name __________________________________ CHE 226 Exam II Fall 2005 7SELECTED CONSTANTS, UNITS, AND CONVERSION FACTORS [The uncertainty in the last digit(s) is shown italicized in parentheses] Atomic mass constant: mu = 1.660 538 73 x 10-27 kg Avogadro’s number: N = 6.022 141 99 (47) x 1023 mol-1 Boltzmann constant: k = 1.380 6503 (24) x 10-23 J/K


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UK CHE 226 - ANALYTICAL CHEMISTRY EXAM II

Course: Che 226-
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