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1 Chemistry 242 Exam 1 Name March 3, 2010! USE PAPER PROVIDED -- ONE SIDE OF PAGE 1. (10 pts) In a Kjeldahl analysis all the nitrogen in a protein sample is converted to NH 3 which is trapped in a standard HCl solution as it is generated. The liberated NH 3 in a 256 µl sample of a solution containing 37.9 mg protein/ml was collected in 5.00 ml of M HCl. After collecting all the NH 3, the excess acid required ml of M NaOH to reach a phenolphthalein endpoint. What is the percent of nitrogen in the protein? 2. (10 pts) AgCl and AgClO 2 are both insoluble in water. In 6 M HNO 3 the AgClO 2 dissolves but AgCl does not. Why does the chlorite dissolve and the chloride not? Include stepwise, net ionic reactions in your explanation. 3. (10 pts) FD&C Blue Dye #1 absorbs at 620 nm. The transmittance of a 5.00 µm Blue Dye solution at 620 nm is This sample was removed from the cuvette, then the cuvette was properly rinsed and filled with a new solution of Blue Dye. The new solution exhibited a transmittance of at the same wavelength. What is the concentration of Blue Dye in this new solution? 4. (10 pts) The weak acid potassium hydrogen phthalate (KHP) is often used as the standard ph 4.01 buffer. Write the charge balance and the phthalate mass balance equations for a M KHP solution. You can abbreviate phthalate as P in your equations. When you are finished with this portion of the exam:! sign the honesty pledge or see the instructor! attach this page to your answer sheets & turn them in! pick up the take home exam

2 Chemistry 242 Exam 1 Take Home Name March 3, 2010 Due Wednesday, March 10, 2010 by 5:00 pm The problems are stated as you might encounter them in the "real world." That means that all the steps needed to arrive at the final answer may not be explicitly stated. Consider all the pertinent aspects of statistical analysis for each problem.! Work on your own, not in groups. Use any books, notes, calculators, and/or computers. You may consult with the instructor for clarification, hints or help in using the computers, but I may not answer all your questions.! Show your work in a logical sequence so I can follow it. Write down enough steps so I can see what you did and locate where you may have made errors.! WORK ON ONE SIDE OF PAGE ONLY! You don t have to use a computer for these problems, but if you do: " Turn in a hard copy of the file and make sure you show the formulas as you entered them (document your formulas) so I can follow your calculations. " Also the spreadsheet file(s) - include Ex1 and your initials in the spreadsheet file name. 1. A quality control lab routinely analyzes mineral tablets for zinc content. Analysis of 5 separate mineral tablets from one batch indicated the zinc contents to be 21.4 mg, 21.2 mg, 20.5 mg, 21.3 mg, and 21.3 mg respectively. For this batch of tablets. a. (10 pts) What are the absolute AND relative 90% confidence intervals for the milligrams of zinc per tablet? b. (5 pts) Suppose ten of the tablets from the above batch are dissolved in a 500±1 ml of water. If the volume uncertainty is a standard deviation for the volume, what is the concentration of zinc (ppm) in the solution and its absolute standard deviation? 2. A particular assay method for protein in corn requires a 14 g sample to achieve a 1% RSD. a. (5 pts) What sample size is required to achieve an 8% RSD? b. (10 pts) If you run assays using the sample size calculated, how many sample replicates must you run to have 95% confidence that the "true value" is within 2% of the average? 3. (10 pts) A company is planning to use a thermal process to produce pellets of a specialty compound. The tolerance of the curing oven occasionally allows the oven to overcure the pellets. The final product is acceptable as long as the overcured pellets constitute no more than 0.5% of the batch. Since overcuring also changes the color of the pellet, it is easy to measure the percent of overcured pellets. The company can adapt an instrument they have to count the total number of pellets and overcured pellets in a sample, but the maximum sample size the instrument will handle is 100,000 pellets. If the analysis of percent overcured pellets must attain a 5%RSD (relative standard deviation), will the modified instrument work for this analysis? Explain your reasoning. 4. The method of standard addition coupled with atomic absorption spectroscopy was used to determine the

3 concentration of Mg +2 in a deionized water sample (Beer s Law). Absorbances were measured at nm. The data is given in Table 1 below. Table 1 ppm Mg +2 Absorbance a. (5 pts) Plot the calibration curve. b. (5 pts) What is the 95% confidence interval for the concentration of Mg +2 in the deionized water. c. (5 pts) What is the corresponding percent relative confidence interval? d. (5 pts) What is the 95% confidence interval for the absorptivity of Mg +2 at nm? DEW, Augustana College 2

4 Chemistry 242 Exam 2 Name April 9, 2010! USE PAPER PROVIDED -- ONE SIDE OF PAGE Explicitly state and verify any assumptions. 1. (15 pts) When copper (II) sulfate is dissolved in water, will the solution be acidic, basic, or neutral? Explain your reasoning using appropriate step-wise, net ionic reactions. 2. (15 pts) What is the ph of 4 x 10-5 M Mg(HSO 4 ) 2? 3. You need to investigate the kinetics of a reaction in aqueous solution at ph 11. a. (10 pts) Which acid-base pair would you choose to make this buffer? Why? (K a table provided). b. (5 pts) What other criteria, besides ability to form the buffer, should be consider in choosing a buffer for this reaction? 4. (20 pts) The ph of a M NaOCN solution is What is the K a of HCNO? 5. A M solution of Ba(OH) 2 is used to titrate ml of M acetic acid. a. (5 pts) Write and balance the net ionic reaction for the titration reaction. b. (20 pts) What is the ph at the equivalence point? c. (10 pts) What indicator would you pick for this titration? Why? (Indicator table provided).

5 Chemistry 242 Exam 3 Name May 7, 2010! USE PAPER PROVIDED -- ONE SIDE OF PAGE ONLY Table of Constants J coul R = F = K mole mole e Ag AgCl reference = V - Nernst Factor at SCE reference = 0.241V 25 C = V 1. (20 pts) In water purification, organics are often removed by distillation from alkaline permanganate which oxidizes the organics to CO 2 and water. Balance the reaction that occurs with propanal. MnO CH 3 CH 2 CHO! MnO 2 (s) + CO 2 2. (20 pts) Chem 120 generates about 2.5 L of 0.10 M Cu +2 solution each year. The copper is recovered by electroplating and the setup I use draws about 100 ma. How many hours will it take to plate all the copper out of this solution? 3. (20 pts) Under standard conditions HNO 3 will oxidize Hg to Hg +2. Will increasing the H + concentration in the solution prevent the oxidation of Hg? Explain your reasoning. 4. (20 pts) What voltage will the following cell produce? Cr 5.00 x 10-4 M Cr x 10-5 M Ni +2 Ni 5. (20 pts) ml of M Cr +3 is titrated potentiometrically with M H 2 O 2 in a solution that is buffered at ph 2.00 using the following cell: The balanced titration reaction is: SCE titration solution Pt H 2 O + 3 H 2 O Cr +3! Cr 2 O H + What voltage does the cell produce after ml of H 2 O 2 has been added? 1