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UK CHE 226 - CHE 226 Exam 2
Course Che 226-
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CHE 226 ANALYTICAL CHEMISTRY Fall 2003 EXAM II -- October 30, 2003 Name ______________________________ WRITE YOUR NAME ON EACH EXAM PAGE NOW. THERE ARE 7 QUESTIONS AND 105 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, as long as the answer is expressed in its final form and all algebraic manipulations and numerical substitutions have been made. Little will be subtracted for routine arithmetic errors. A calculator may be used, but not shared with anyone else. A sheet of scrap paper is at the back of the exam booklet. Tear it off now. 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 ___________ /28 Question 7 ___________ /13 QUESTION 2 ___________ /8 Question 8 ___________ / QUESTION 3 ___________ /8 Question 9 ___________ / QUESTION 4 ___________ /24 Question 10 ___________ / QUESTION 5 ___________ /10 Question 11 ___________ / QUESTION 6 ___________ /14 TOTAL ___________ /105Name __________________________________ 1. (28 points) Barium iodate, Ba(IO3)2, is relatively insoluble, Ksp = 1.57 x 10-9. Iodic acid, HIO3, is a fairly strong “weak acid”, with Ka = 1.7 x 10-1. You wish to calculate the solubility of barium iodate in a solution that is also 0.01 M in iodic acid. Because it is such a strong “weak acid”, you must use the full systematic approach to solving this problem. [Set the problem up, do not try to solve it numerically.] (a) (10 points) Accurately write all the equilibrium reactions for this problem along with their associated equilibrium constant expressions. (b) (5 points) List all the solution concentrations that are not known. (c) (8 points) Write the mass balance equations for this system. Let the solubility of barium iodate be called S. CHE 226 Exam II Fall 2003 2Name __________________________________ (d) (5 points) Write the charge-balance expression for this solution. 2. (8 points) A 0.7406-g sample of impure magnesite, MgCO3 (84.31 g/mol), was decomposed with HCl; the liberated CO2 (44.01 g/mol) was collected on calcium oxide and found to weigh 0.1881 g. Calculate the percentage of magnesium (24.305 g/mol) in the sample. 3. (8 points) A 0.3367 g sample of primary standard grade Na2CO3 (105.99 g/mol) required 28.66 mL of H2SO4 to reach the endpoint in the neutralization reaction below. Calculate the molarity of the H2SO4 solution. CO32- + 2 H+ Æ H2O + CO2 CHE 226 Exam II Fall 2003 3Name __________________________________ 4. (24 points) Calculate the pH of the following aqueous solutions. a. Saturated Pb(OH)2. Ksp = 1.2 x 10-15. b. 0.075 M sodium hypochlorite, NaOCl. The Ka for hypochlorous acid is 3.0 x 10-8. c. A solution prepared by mixing 100 mL of 0.075 M NaOCl and 100 mL of 0.050 M HCl. CHE 226 Exam II Fall 2003 4Name __________________________________ 5. (10 points) The pH of blood is maintained fairly closely to 7.40 by the body, primarily by a relatively high concentration of a “carbonate” buffer. The pKa’s for carbonic acid, H2CO3, are 6.35 and 10.33. Calculate the ratio of the concentration of the bicarbonate ion concentration, [HCO3-], to that of carbonic acid at this pH. 6. (14 points) Biochemists often use the term “monophosphate” to indicate the inorganic phosphate ion in its various states of protonation in cells and fluids. The pKa’s for phosphoric acid are 2.15, 7.20, and 12.15. Calculate the fraction (α) of the total phosphate in solution that exists in the form of HPO42- at the physiological pH of 7.40. CHE 226 Exam II Fall 2003 5Name __________________________________ CHE 226 Exam II Fall 2003 67. (13 points) Calculate the pH of a 0.050 M solution of iodic acid, HIO3, which has a Ka = 1.7 x


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UK CHE 226 - CHE 226 Exam 2

Course: Che 226-
Pages: 6
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