CHEMISTRY 1128 FINAL EXAM May 4, Name Section Signature TA ID#

Transcription

1 CHEMISTRY 1128 FINAL EXAM Name Section Signature TA ID# PLEASE READ THE FOLLOWING INSTRUCTIONS Do NOT begin the exam until asked to do so. There are 12 numbered pages, and a separate section with a page of equations and a periodic table in this exam. Check to see that they are all here before you begin the exam. Return only the section with the numbered pages when you are finished. Write your name on every page. Use a pen with blue or black ink for the entire exam. Be sure to follow the directions in answering all questions. In working the problems and the BONUS, you MUST SHOW ALL WORK. No credit will be given unless all work is clearly shown and the method of solution is logically correct. Use appropriate units and significant figures. For those who have an excused absence from an hourly exam, and are using part of this final as credit for that exam: You may want to spend extra time on a particular portion of this exam that corresponds to the hourly exam that you missed. EXAM SCORES WILL BE POSTED ON HuskyCT, MAY 8 AT 5:00 PM. Page Total Grader Page Total Grader 1 /24 7 /10 2 /22 8 /25 3 /22 9 /16 4 /18 10 /24 5 /20 11 /12 6 /15 12 /42 TOTAL /250

2 Name I. (68 points) This part of the final corresponds to Exam I. It covers the material in Chapters 10, and 11. A. (12 points) On the blanks provided, write True if the statement is correct or False if the statement is incorrect. 1. HF is more soluble than CHCl 3 in water. 2. The freezing points of aqueous solutions of 1.0 m NaCl and 1.0 m glucose, C 6 H 12 O 6 solution are equal. 3. For an exothermic reaction, the rate constant k will always decrease with temperature increase. 4. The rate constant for any order reaction increases when the initial concentration of the reactants are increased. 5. For the reaction A B, where K = 8, for 2A 2B, K = The reaction quotient Q and the equilibrium constant, K, always have the same numerical value. B. (12 points) Reagent grade nitric acid is 71.0% nitric acid by mass and has a density of g/ml. 1. What is the molarity of the nitric acid solution? 2. If ml of the nitric acid is diluted with water to make a 3.00 L of solution, what is the molarity of the diluted solution? 1

3 Name C. (12 points) The vapor pressure of CCl 4 (MM = g/mol) at 65 C is 504 mm Hg. How many grams of C 10 H 8, (MM = g/mol) must be added to g of CCl 4 so that the vapor pressure of CCl 4 over the solution is 483 mm Hg? Assume the vapor pressure of naphthalene, C 10 H 8, at 65 C is negligible. D. (10 points) Dinitrogen pentoxide gas decomposes to form nitrogen dioxide and oxygen. The reaction is first order and has a rate constant of h What is the half life for the reaction? 2. If a 2.50 L flask originally contains N 2 O 5 at a pressure of 756 mm Hg at 25 C, then how many moles of O 2 are formed after 135 minutes? 2

4 Name E. (10 points) Twenty grams of solid PH 3 BCl 3 are sealed in a 5.0 L flask and heated to 80 C. The following reaction takes place PH 3 BCl 3 (s) PH 3 (g) + BCl 3 (g) At equilibrium the total pressure for PH 3 and BCl 3 (taken together) is 0.46 atm. What is the equilibrium constant at this temperature? F. (12 points) For the equilibrium 2IBr(g) I 2 (g) + Br 2 (g) K = 8.5 x 10-3 at 150 C If atm of IBr is placed to a 2.0 L container, what is the partial pressure of IBr after the equilibrium is reached. 3

5 Name II. (63 points) This part of the final corresponds to Exam II. It covers the material in Chapters 13, 14, and 15. A. (14 points) Consider 4 test tubes, each containing ml of the following aqueous solutions. Answer as GT (greater than), LT (less than), EQ (equal to) or MI (more information needed. A = 0.10 M HBr B = 0.10 M HNO 2 C = 0.10 M NaOH D = 0.10 M NH 3 (aq) 1. ph of A ph of B. 2. ph of B ph of C ph of D. 4. % ionization of A % ionization of C. 5. When 1.00 L of solution of C is added to 1.00 L solution of D, a solution is obtained where the moles of OH Answer the questions below. On the blanks provided, write Y if the statement is correct or N if the statement is incorrect. 6. For an insoluble metal salt, K sp, is always less than More PbCl 2 can be dissolved at 100 C than at 25 C. One can conclude that dissolving PbCl 2 is an endothermic process. B. (12 points) A sample of g of an unknown monoprotic acid was dissolved in 25.0 ml of water and titrated with M NaOH. The acid required 27.4 ml of base to reach the equivalence point. 1. What is the molar mass of the acid? 4

6 Name 2. After 15.0 ml of base was added in the titration, the ph was found to be What is the K a for the unknown acid? C. (12 points) A 0.15 M solution of weak acid is 3.0% ionized. 1. What is the [X - ] for the solution described above? 2. What is the ph of the solution? 3. What is the acid dissociation constant, K a, for the weak acid? 5

7 Name D. (15 points) A 50.0 ml of M lactic acid (HLac) with a K a value of 1.38 x 10-4 is titrated with M NaOH. 1. What volume of NaOH is required to reach equivalence point? 2. What is the ph of the solution before any sodium hydroxide is added? 3. What is the ph at the equivalence point? 6

8 Name E. (10 points) A saturated solution of silver(i) sulfate, Ag 2 SO 4, at 25 C is prepared by dissolving 1.2 g of silver (I) sulfate in water to make ml of solution. What is the K sp for silver (I) sulfate? 7

9 Name III. (77 points) This part of the final corresponds to Exam III. It covers the material in Chapters 15, 16, and 17. A. (15 points) Answer the questions below. On the blanks provided, write Y if the statement is correct or N if the statement is incorrect. 1. At equilibrium, ΔG = For a reaction where ΔH > 0 and ΔS < 0, the reaction is spontaneous in the reverse direction. 3. Give the symbol for the metal that will reduce Ba 2+ to Ba, but will not reduce Li + to Li. 4. E red values for half cells are measured by comparison with standard electrode. 5. The number of moles of Fe 2+ that can be oxidized to Fe 3+ by reaction with one mole of MnO - 4 (which is reduced to Mn 2+ ) is. B. (10 points) For the reaction 2H 2 O (l) + 2Cl - (aq) H 2 (g) + Cl 2 (g) + 2OH - (aq) (kj/mol) G f 1. Calculate ΔGº at 25ºC. 2. Calculate ΔG at 25ºC when PH P 0.250atm, [Cl - ] = M, and the ph of the solution is c 2 8

10 Name C. (8 points) What is the temperature at which the vaporization of CHCl 3 (l) becomes spontaneous? CHCl 3 (l) CHCl 3 (g) Sº (J/mol K) f (kj/mol) D. (8 points) Consider the following voltaic cell where sulfide is oxidized: Pt S 2-, S NO 3 -, NO Pt (basic solution) 1. Write the balanced cell reaction. 2. Calculate E for the cell. 9

11 Name E. (12 points) Consider the following reaction at 25ºC in a basic solution: 2Fe(OH) 3 (s) + NO 2 - (aq) NO 3 - (aq) + H 2 O + 2Fe(OH) 2 (s) 1. What is Eº? 2. What is n? 3. What is Gº? 4. What is K? F. (12 points) Consider a voltaic cell in which the following reaction takes place. 2Fe 2+ (aq) + H 2 O 2 (aq) + 2H + (aq) 2Fe 3+ (aq) + 2H 2 O E o = V Calculate E under the following conditions: [Fe 2+ ] = M, [H 2 O 2 ] = M, [Fe 3+ ] = M and ph =

12 Name G. (12 points) An electrolytic cell produces aluminum from Al 2 O 3 at the rate of ten kilograms a day. Assume a yield of 100%, 1. How many moles of electrons must pass through the cell in one day? 2. How many amperes are passing through the cell? 11

13 Name IV. (42 points) This part of the final corresponds to Chapter 18. A. (15 points) Answer the questions below, using LT (for is less than), GT (for is greater than), EQ (for is equal to) or MI (for more information required) in the blanks provided. You may use True or false whenever it is necessary. 1. The mass number increases with beta emission. 2. The number of neutrons in an α particle the number of neutrons in Li The number of protons in Cm-242 before β-emission the number of protons in the resulting nucleus after β-emission. 4. A radioactive species with a large rate constant, k, decays very slowly. 5. The mass of a positron the mass of electron. B. (15 points) Complete the following nuclear equations. Write your answers in blanks provided Th Pa U n Xe 2 n H Po n Mo He 42 2 C. (12 points) A 1.0 mg sample of technetium-99 has an activity of 1.7 x 10-5 Ci, decaying by beta emission What is the decay constant for 43 Tc? What is the half-life of this isotope in years? 12