4. Hydrogen-oxygen fuel cells are utilized in some cities to produce electricity. The fuel cell reaction and the standard cell potential are:

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1 Hour Exam I Page 1 1. Consider the following reactions for which the sign of the enthalpy change is given. Which of the reactions can never be spontaneous at any temperature? a. 2 H202(l) -> 2 H20(l) + 02(g) AH(-) b. 302(g) ^ 203(g) AH(+) c. CaC03(s) CaO(s) + C02(g) AH(+) d. 4 Fe(s) (g) 2 Fe203(s) AH(-) 2. Which of the following statements is false? a. The sign of AG for a reaction indicates whether the reaction is spontaneous. b. If AG is positive for a reaction, then K is less than 1 (K < 1). c. When Q = K for a reaction, then AG = 0. d. The entropy of the universe is increasing. e. The equilibrium position represents the highest free energy state available to a reaction. 3. Which of the following statements is false regarding electrochemical cells? a. Galvanic cells utilize spontaneous oxidation-reduction reactions. b. Electrolytic cells are based on oxidation-reduction reactions having positive AG values. c. The cell potential (Eceii) in a concentration cell is produced by constructing a galvanic cell where both the anode and cathode compartments contain the same components but at different ion concentrations. d. When the concentration of a reactant ion in a galvanic cell is increased, the cell potential (Eceii) decreases. e. Batteries are examples of galvanic cells. 4. Hydrogen-oxygen fuel cells are utilized in some cities to produce electricity. The fuel cell reaction and the standard cell potential are: 2 H2(g) + 02(g) ^ 2 H20(l) E^ = 1.23 V Calculate the maximum amount of work this fuel cell reaction could produce for the production of 2 mol of H20(l) assuming standard concentrations and T = 25 C. a kj b kj c kj d kj e kj

2 Hour Exam I Page 2 5. Consider the following standard reduction potentials: E (volts) F2 + 2e" 2F~ 2.87 Ag^ + e" ^Ag 0.80 Cu2^ + 2e" ^Cu 0.34 Pb^^ + 2e"-^Pb Ni^* + 2e" ^ Ni -0.23t Assuming standard conditions, copper (Cu) will spontaneously reduce which of the following? a. Ag and F~ b. Ag"^ and F2 c. Pb and Ni d. Pb^ and Ni^"^ e. none of these 6. Cadmium sulfide (CdS) is used in some semiconductor applications. Calculate the value of the solubility product (Ksp) for CdS given the following standard reduction potentials. CdS + 2e" Cd + S^ E =-1.21V Cd^^ + 2e" ^ Cd E =-0.40 V a. 3.9x10"^^ b. 3.3x10"^^ c. 2.1 x 10~"^ d. 3.0x10^^ e. 2.6x10^^ 7. Consider the following reduction potentials: E Cl2 + 2e" 2Cr 1.36 V O e" -> 2 H2O 0.82 V 2 H2O + 2e" ^ H H~ V Na* + e" Na V When molten NaCl is electrolyzed, Na(s) and ClaCg) are produced. When aqueous NaCl is electrolyzed, H2(g) and Cl2(g) are produced. Which of the following statements best explains why H2(g) is produced instead of Na(s) in an aqueous solution of NaCl? a) H2O is more easily reduced relative to Na. b) H2O is more easily oxidized relative to Na. c) H2O is more easily reduced relative to Na^. d) H2O is more easily oxidized relative to Na"^.

3 Hour Exam I Page 3 8. Which of the following statements if false? a. Corrosion involves the oxidation of iron. b. Corrosion is an example of an electrolytic cell. c. Sacrificial metals (or cathodic protection) utilize metals that are more easily oxidized than iron. d. Dry climates tend to have less of a problem with corrosion as compared to climates with ample moisture. e. Paint or protective oxides can help prevent corrosion by eliminating contact of the iron with 02(g). ^ 9. How many of the following four relationships describe a basic solution? [Hi < 1.0 X 10"^ M; poh < 7.00; ph > 7.00; [OIT] > 1.0 x 10"^ M a. O(None) b. 1 c. 2 d. 3 e. 4 (All describe a basic solution.) 10. Consider several 1.0 M solutions each containing a different acid, HA. How many of the following four statements (I-IV) is/are true? I. As the Ka value of the acid increases, the ph of the solution increases. II. As the Ka value of the acid increases, the percent dissociation of the acid increases. III. As the Ka value of the acid increases, the [H"^] of the solution increases. IV. As the Ka value of the acid increases, the Kb value for the conjugate base decreases. a. 0 (none) b. 1 c. 2 d. 3 e. 4 (All statements are true.) 11. One mole of a weak base, B, is dissolved in 1.0 L of water and no other substance is added. Which of the following, to a close approximation, is true? a. [BH1>[B] b. [B] = [OH] c. [BH^ = [OH] d. [Hl>[OH-] e. [BHl>[OH"]

4 Hour Exam I Page H2SO4 is a diprotic acid with the following Ka values: H2SO4 ^ HSO4" + H^ Kai = 1 X 10^ HSO4" S04^" + H^ Ka2= 1.2x 10" r2 Which of the following statements (a-c) is true? a. The ph of a 0.10 M H2SO4 solution should be peater than one (ph > 1.00). b. HSO4" is a stronger acid than H2SO4. c. HSO4" is a stronger base than S04^~. d. None of the above statements (a-c) are true. 13. Which of the following compounds will not contribute to the acid rain problem, i.e., will not form an acidic solution when dissolved in water? a. Na20 b. SO2 c. SO3 d. NO2 e. CO2 14 The equilibrium constants Ka and Kb refer to specific reactions. Which of the following four reactions (a-d) is incorrectly matched with the equilibrium constant? a. HCN^H* + CN~ Ka for HCN b. HONH2 + H2O ^ HONHs^ + OET KbforHONH2 c. d. e. F + H2O OH" + HE Kbforl^ NH4* i:; NH3 + H^ Ka for NEU^ All the above reactions are correctly matched with the equilibrium constant.

5 Hour Exam I Page 5 The next three questions refer to the titration of ml of 0.40 M HOBr by 0.20 M KOH. The Ka value for HOBr is 2.0 x 10"^ 15. Calculate the ph after 50.0 ml of KOH has been added. a b c d e Calculate the ph after ml of KOH has been added. a b c d e Calculate the ph after ml of KOH has been added. a b c d e Arrange the following 0.10 M solutions in order of increasing ph: HI, HF, NaF, Nal a. HI < HE < NaF < Nal b. HI < HF < Nal < NaF c. HF < HI < Nal < NaF d. HF < HI < NaF < Nal e. NaF < Nal < HI < HF 19. When first studying acid-base chemistry, students sometimes assume that the conjugate base of a weak acid is a strong base. However, this assumption is false. Which of the following best explains why the conjugate base of a weak acid is not a strong base? a. The conjugate bases of weak acids all have Kb values greater than 1. b. The conjugate bases of weak acids all have Kb values equal to 1. c. The conjugate bases of weak acids all have Kb values less than 1. d. The conjugate bases of weak acids all have Kb values less than Kw (= 1.0 x 10"^"^).

6 Hour Exam I Page Consider 0.25 M solutions of each of the following potassium salts: KCl, KI, KBr, KNO3 How many of the solutions are basic? a. O(none) b. 1 c. 2 d. 3 e. 4 (All are basic solutions.) 21. Consider the following reaction at some constant temperature: 12(g)+ H2(g) ^2HI(g) K = 0.75 Initially, 2.0 mol of I2, 2.0 mol of H2 and 2.0 mol of HI are mixed together in a 1.0 L rigid container and are allowed to react to reach equilibrium. Which of the following statements is true once this reaction reaches equilibrium? a. At equilibrium, [I2] > [HI]. b. At equilibrium, [I2] = 2.0 M. c. At equilibrium, [I2] > [H2]. d. At equilibrium, [H2] < 2.0 M. e. At equilibrium, [HI] = 2.5 M. 22. Which of the following solutions has poh = 3.00? a. 3.0MNaOH b. 5.0 x 10"^MCa(OH)2 c. 1.0 x 10"^^ MHCl d. 3.0MHC1 e. 1.0 x 10"^^ MNaOH 23. The [H""] in a buffer solution consisting of HONH3CI and HONH2 is equal to the Ka value for HONHs^ ([H^] = Ka = 9.1 x 10"^ M). Which of the following statements about this solution is true? a. In this solution, the concentration of HONHs"^ equals the concentration of HONH2 ([HONH3I = [HONH2]). b. If NaOH is added to this solution, the ph will decrease. c. If HCl is added to this solution, the [H^] will decrease. d. If HCl is added to this solution, the concentration of HONHs"^ will decrease and the concentration of HONH2 will increase. e. The ph of this solution would be lower than the ph of a solution where the concentration of HONHs"^ is greater than the concentration of HONH2 ([HONH3I > [HONH2]).

7 Hour Exam I Page A solution is to be buffered at ph = 4.5. Which of the following pairs of substances would be the best choice for buffering this solution? a. HNO2 (Ka for HNO2 = 4.0 x 10"^) and KNO2 b. HOCl (Ka for HOCl = 3.5 x 10"^) and Ca(OCl)2 c. HCIO4 (Ka for HCIO4-10^) and NaC104 d. CH3NH2 (Kb for CH3NH2 = 4.4 x 10""^) and CH3NH3NO3 e. C6H5NH2 (Kb for C6H5NH2 = 3.8 x 10"^^) and C6H5NH3CI ^ 25. Consider the following reaction at equilibrium: N2(g) + 3 H2(g) ^ 2 NH3(g) AH = kj (exothermic) Which of the following changes will shift the equilibrium to the right (to products)? 1. increasing the temperature 2. decreasing the temperature 3. increasing the volume of the reaction container 4. decreasing the volume of the reaction container 5. removing some NH3 6. adding some NH3 7. removing some N2 8. adding some N2 a. 1, 4, 6, 7 b. 2, 3, 5, 8 c. 1, 6, 8 d. 2, 4, 5, 8 e. 1, 3, 5, 7

8 Hour Exam II Page 8 Written out problems - Show all work for partial credit. 26. Consider a galvanic cell at 25''C based on the following half-reactions: (12pts) Al^^ + 3e" ^ Al E = V Ni^^ + 2e" -> Ni E = V a) Draw the cell under standard conditions labeling the anode, the cathode, the ^ direction of electron flow, the concentration of ions, the electrodes, and the direction of flow of cations and anions through the salt bridge. b) To the standard cell above, OH" is added to the aluminum compartment causing Al(OH)3(s) to precipitate. After precipitation of Al(OH)3(s) has ceased, the concentration of OH" is 1.0 X 10""^ M and the measured cell potential is 1.82 V. Calculate the Ksp value for Al(OH)3(s). Al(OH)3(s) ^ Ar^(aq) + 3 OHr(aq) Ksp =?

9 Hour Exam 11 Page Consider an aqueous solution of copper nitrate, Cu(N03)2. It took 1380 seconds using a current of 2.00 A to plate out all the copper from 25.0 ml of the copper nitrate solution. What was the original concentration of copper nitrate in the solution? Calculate the concentration in units of molarity (= mol/l). (4 pts) 28. Consider a weak acid, HX. If a 0.10 M solution of HX has a ph of 5.83 at 25 C, what is AG for the acid's dissociation reaction at 25 C? (6 pts) HX(aq) ^ ir(aq) + X~(aq) AG =?

10 Hour Exam II Page Consider the following solutions for the next three questions. (13 pts) I ml of 0.50 M (C2H5)3N (Kb for (C2H5)3N = 4.0 x 10"^) II ml of 0.30 MHCIO4 III ml of 0.30 M KOH IV ml of 0.50 M (C2H5)3NHI a. Calculate the ph of solution IV. b. Calculate the ph of the resulting solution when solutions I, III, and IV are mixed together. c. Calculate the ph of the resulting solution when solutions I, II, III, and IV are mixed together.

11 Hour Exam 11 Page Consider the following two titrations: (18 pts) a ml of M HCIO4 titrated by M KOH. b ml of M HONH2 (Kb = 1.1 x 10"^) titrated by 1.00 M HBr. For each of the two titrations, determine the ph at the halfway point to equivalence and the ph at the equivalence point. Also sketch the general shape of each titration curve showing the ph of the two points that you calculated. In order to receive credit, you must show all work. An answer With no supporting work will be marked as incorrect. Determine all ph values to 2 decimal places. a ml of M HCIO4 titrated by M KOH b ml of M HONH2 (Kb = 1.1 x 10"') titrated by 1.00 M HBr

CHEMISTRY 102 Fall 2010 Hour Exam III. 1. My answers for this Chemistry 102 exam should be graded with the answer sheet associated with:

CHEMISTRY 102 Fall 2010 Hour Exam III. 1. My answers for this Chemistry 102 exam should be graded with the answer sheet associated with: 1. My answers for this Chemistry 10 exam should be graded with the answer sheet associated with: a) Form A b) Form B c) Form C d) Form D e) Form E Consider the titration of 30.0 ml of 0.30 M HCN by 0.10