SHOW YOUR WORK. NO WORK, NO CREDIT

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1 Chemistry 4 Exam Name (print) February 4, 07 On my honor, I pledge that I have upheld the Honor Code, and that the work I have done on this assignment has been honest, and that the work of others in this class has, to the best of my knowledge, been honest as well. Signed If you feel you can t sign this, contact the instructor ( or in person) Equations and Constants -4 A -log(t) K w.00 x 0 KaK b E cell E red - E ox E right - E left E ir G -nfe G -RT ln(k eq ) E log (K eq ) at 5 n RT E E - ln (Q) E E - log (Q) at 5 E SCE 0.4 V E AgCl/Ag 0.97 V nf n coul coul J A J coul V F R 8.34 q nf it - s mole e mole K na nb tss p q p- σ n npq K s mr n na nb na nb e -0.5 z μ μ ciz i log γ α μ 305 ' t r r ' r o r - t ' t t t- t k r N α - k N k α R ' ' w/ wb to k w b w b / 4 α k B back width at 0% height H A C s Cm μ A μ front width at 0% height SHOW YOUR WORK. NO WORK, NO CREDIT (pts each) Circle the correct answer.. Several fields near a stream were sprayed with an organic insecticide (amine derivative). Irrigation water from those fields drains into the stream. In order for the stream water to be safe for livestock to drink, the pesticide level must be less than 50 ppb. Gas chromatography works well to analyze for the pesticide, but the detection limit is ppm (000 ppb). What would be the best preconcentration method to use for this sample? a. derivatization to an ester. b. trap the insecticide on an anion exchange membrane. c. precipitate with sulfide and filter. d. extract into hexane.. Quantitating an unknown requires comparing to standards. This may be done in one of three ways: use a calibration curve; use standard addition; or use an internal standard. The calibration curve method would be used when a. a calibration curve is not linear. b. the standard and analyte have similar characteristics that are unaffected by the other material in the sample. c. the quantity of sample analyzed or the instrument response varies from run to run. d. the sample composition is unknown or complex and affects the analytical signal. (rest of exam on the back)

2 3. Which of the statements below are TRUE for converting a concentration of a 54.9 ppm Fe solution to molarity? I II III IV Iron s molar mass must be known to calculate the moles iron in solution. Iron s density must be known to calculate the mass of iron in solution. The solution density must be known to calculate the solution volume. The type of glassware used to prepare the solution must be known. a) I, III, and IV b) I and II c) I and III D) II and III 4. occurs when a species other than analyte increases or decreases the analytical signal and makes it appear that the concentration is greater or less than the real concentration. a) Interference b) Masking c) Aliquots d) Disruption 5. Which of the following is NOT true for linear regression? a. minimizes the x and y distances of the data from the best fit line. b. assumes there is no error in the x values. c. assumes the uncertainty is about the same for all the y values. d. can derive analytical expressions (equations) for the standard deviations of slope, y-intercept, and x- intercept. On the rest of the exam: q INCLUDE LABELS AND PROPER NUMBER OF SIG FIGS q USE PAPER PROVIDED -- ONE SIDE OF PAGE q NAME OR INITIALS ON EACH PAGE. q UP TO 75% OF THE CREDIT GIVEN FOR CORRECT SET UP, INCLUDING LABELS AND SIG FIGS. 6. (0 pts) Calculate the concentration of Fe(CN) 6 4- in a 0.0 M ZnSO 4 solution that is saturated with Zn Fe(CN) 6. Assume that the K sp equilibrium is the only important equilibrium reaction. K sp Zn Fe(CN) 6 =. x (0 pts) An aliquot of a compound with a molar mass of 9.6 g/mole was dissolved in a 5.00 ml. Then.00 ml was diluted to 0.00 ml. The absorbance of the final solution, measured at 340 nm in a.000 cm cuvette, was The molar absorptivity of the compound at 340 nm is 630 M - cm -. What is the original concentration of the compound (in the 5 ml)? 8. (0 pts) A Na CO 3 standard solution is prepared by transferring.487 grams of primary standard-grade sodium carbonate to a 50.0 ml volumetric flask, dissolving the sample in ~00 ml of distilled, deionized water and diluting to the mark. A 5.00 ml aliquot of this solution requires 4.65 ml of HCl solution to reach the equivalence point. Calculate the concentration of the HCl solution. 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

3 Chemistry 4 Exam Take Home Name (print) February 4, 07 Due Wednesday, March 3, 07 by 5:00 pm On my honor, I pledge that I have upheld the Honor Code, and that the work I have done on this assignment has been honest, and that the work of others in this class has, to the best of my knowledge, been honest as well. Signed If you feel you can t sign this, contact the instructor ( or in person) SHOW YOUR WORK. NO WORK, NO CREDIT 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! NAME OR INITIALS ON EACH PAGE.! INCLUDE LABELS AND PROPER NUMBER OF SIG FIGS! UP TO 75% OF THE CREDIT GIVEN FOR CORRECT SET UP, INCLUDING LABELS AND SIG FIGS.! You don t have to use a computer for these problems, but if you do: " Turn in a hard copy of the file including appropriately annotated graph(s) and make sure you show the formulas as you entered them (document your formulas) so I can follow your calculations. " Also drop the spreadsheet file(s) in Moodle - include Ex and your initials in the spreadsheet file name.. (0 pts) A student standardized a sodium hydroxide solution using KHP and obtain the following concentrations: 0.08 M, 0.03 M, 0.00 M, M and 0.06 M. What are the absolute and relative 95% confidence intervals for the average concentration?. (5 pts) The density of a solution is determined using a class A 5 ml volumetric flask ( ± 0.03 ml) and an analytical balance. The mass of the empty volumetric flask is ± g, and the mass of the flask filled with solution is ± g. a. What is the density of the solution? b. What is the absolute uncertainty for the density? 3. In the production of a certain brand of vitamin enriched cat food, the sampling standard deviation for a 4.7 g sample is 4%. a. What mass of sample is required to decrease the sampling standard deviation to %? b. A vendor of pet foods for exotic animals requires their suppliers to ensure that their products have a relative 95% confidence interval for the assay of % or less. How many 4.7 g samples (4% sampling standard deviation) must the cat food producer analyze to meet the vendor's uncertainty requirement? (rest of exam on back)

4 4. (0 pts) A thermosetting polymer is supplied as a pellet mixture containing.5% polymer A pellets and 97.5% polymer B pellets. How many particles must be sampled to produce an analysis for polymer A with a relative standard deviation that is less than 3%? 5. Tooth enamel consists mainly of the mineral calcium hydroxyapatite Ca 0 (PO 4 ) 6 (OH). Trace elements in teeth provide archeologists with clues about diet and diseases in ancient peoples. In one study of ancient teeth, strontium levels were determined by a standard addition method using atomic absorption spectroscopy. A ppb standard Sr solution was prepared. A 750 mg sample of tooth was dissolved and diluted to 0.00 ml. Then analysis solutions were prepared using the table below. Calibrated microliter pipets and volumetric flasks were used to make all solutions in the table. Calibration Curve Data vol tooth soln (μl) vol Sr standard (μl) final vol (ml) Absorbance a. (6 pts) Graph the calibration curve. b. (7 pts) What is the absolute 95% confidence interval for the Sr concentration (ppb) in the tooth expressed with the appropriate number of significant figures. c. (7 pts) What is the relative 95% confidence interval for the slope of the calibration curve? You can do part b and c in the spreadsheet or separately on paper. Clearly show your work. Turn in a hard copy of the file including appropriately annotated graph(s) and make sure you show the formulas as you entered them (document your formulas) so I can follow your calculations. Drop electronic copies of the spreadsheet file(s) in Moodle - include your initials and Ex in the spreadsheet file name.

5 Chemistry 4 Exam Name print March 9, 07 On my honor, I pledge that I have upheld the Honor Code, and that the work I have done on this assignment has been honest, and that the work of others in this class has, to the best of my knowledge, been honest as well. Signed If you feel you can t sign this, contact the instructor ( or in person) (pts each) Circle the correct answer.. The buffer needed for a capillary electrophoresis experiment must have a ph of 0.0. Which weak acid is the best choice to make this buffer? A) ammonium chloride (pka = 9.4) B) disodium phosphate (pka =.38) C) 3-(cyclohexylamino)propanesulfonic acid (pka = 0.40) D) any weak acid should work. Which of these will form an acidic solution when added to water? Circle all that apply. A) AgCl B) NO (g) C) CaSO 3 D) CH 3 NH 3. - When HSO 3 is dissolved in water, it can act as either a weak acid or a weak base. The ph of that solution A) is 7, because the acid neutralizes the base. B) is determined from only the base equilibrium. C) is determined using both equilibria. D) is determined from only the base equilibrium. 4. Which indicator would work best for the titration of HCl (flask) with KOH (buret)? A) phenolphthalein (pk a 9.6) B) bromothymol blue (pk a 7.) C) methyl yellow (pk a 3.) D) can't determine from information given 5. Which of the following are soluble in water? Circle all that apply. A. Fe(C H 3 O ) 3 B. AgCl C. (NH 4 ) CO 3 D. HF (remainder of the exam on the back)

6 On the rest of the exam: SHOW YOUR WORK. NO WORK, NO CREDIT! INCLUDE LABELS AND PROPER NUMBER OF SIG FIGS! USE PAPER PROVIDED! NAME OR INITIALS ON EACH PAGE.! UP TO 75% OF THE CREDIT GIVEN FOR CORRECT SET UP, INCLUDING LABELS AND SIG FIGS. 6. (0 pts) What is the ph of a saturated solution of La(OH) 3? (K sp = x 0 - ) Assume that La(H O) 6 +3 gives a negligible contribution to the ph. 7. (0 pts) When g of a diprotic acid was titrated with M NaOH, it took 5.8 ml to reach the second equivalence point. What is the molar mass of the acid? 8. (5 pts) How many milliliters of M hydrochloric acid must be added to 00.0 ml of M ethylamine to produce a ph 0.00 buffer? (K a. x 0 - ) Explicitly state and check any assumptions made. 9. (5 pts) Set up the system of mathematical equations (not just reactions) needed to solve the problem below without making assumptions. DO NOT SOLVE, JUST SET UP THE EQUATIONS. What is the ph of a solution that is 0.5 M Na SO 3 and 0.48 M H SO 3. Use K a, K a, etc. instead of numbers in your K expressions. Don t forget the Honesty Pledge

7 Chemistry 4 Exam 3 Name print May 3, 07 Equations and Constants are on the back of the periodic table. On my honor, I pledge that I have upheld the Honor Code, and that the work I have done on this assignment has been honest, and that the work of others in this class has, to the best of my knowledge, been honest as well. Signed If you feel you can t sign this, contact the instructor ( or in person) (pts each) Circle the correct answer.. The cell potential for a galvanic cell with a large equilibrium constant is A) negative B) positive C) zero voltage D) impossible to predict. We have used concentrated HNO 3 in several labs this semester. Circle all the hazards below that are associated with this reagent. a. compressed gas hazard b. corrosive c. flammable d. strong oxidizer 3. What is the reducing agent in the reaction: MnO + Cl H +! Cl + Mn + + H O? a. MnO b. Mn c. Cl - d. Cl 4. Which of the following will reduce H SO 3 under standard conditions? - a. I 3 b. Fe + c. Sn + d. none of these 5. In which solution is a glass ph electrode likely to show a ph that is lower than the actual ph? A) deionized water B) 0.0 M KH PO 4 C) 0. M HCl D) 0. M NaOH (remainder of the exam on the back)

8 On the rest of the exam: SHOW YOUR WORK. NO WORK, NO CREDIT! INCLUDE LABELS AND PROPER NUMBER OF SIG FIGS! USE PAPER PROVIDED! NAME OR INITIALS ON EACH PAGE.! UP TO 75% OF THE CREDIT GIVEN FOR CORRECT SET UP, INCLUDING LABELS AND SIG FIGS. 6. For the cell diagram below: Pt HOCl (aq, M), HClO (aq, M), H + (aq, M) MnO 4 - (aq, M), H + (aq, M) MnO (s) Pt a. (0 pts) Write and balance the cell reaction. b. (5 pts) If E for the left half-reaction is V, what is K eq for this reaction? (The right half-reaction E is in the table). 7. (0 pts) A 0.00 ml sample of 0.00 M Cr + is titrated with a 0.00 M Sn 4+ solution and the titration is followed potentiometrically. The unbalanced titration reaction is Sn 4+ + Cr +! Sn + + Cr 3+. What is the voltage of the cell after 0.00 ml of Sn 4+ has been added. The cell for following the reaction is: SCE Cr +, Cr 3+, Sn 4+, Sn + Pt 8. (5 pts) A bumper with a surface area of 7500 cm needs a chromium layer cm thick for adequate corrosion protection. How long will it take to plate that bumper from a Cr 3+ bath using a current of.0 ka? The density of Cr is 7.5 g/cm (0 pts) By how many volts will the potential of an ideal Mg + ion-selective electrode change if the electrode is moved from a.00 x 0-4 M MgCl solution to a.00 x 0-3 M MgCl solution? Don t forget the Honor Pledge