State University of New York at Binghamton, Department of Chemistry Chemistry 108, Introductory Chemistry II, Exam 3, Version A

State University of New York at Binghamton, Department of Chemistry Chemistry 108, Introductory Chemistry II, Exam 3, Version A 1. A reaction will always be spontaneous if: a. H is + & S is + b. H is – & S is – c. H is – & S is + d. H is + & S is – e. H is + & S is 0 2. In the following reaction, which substance is behaving as a reducing agent? Cr2O72(aq) + 3Ni(s) + 14H+(aq)  3Ni2+(aq) + 2 Cr3+(aq) + 7H2O a. Cr2O72 b. Ni c. H+ d. Ni2+ e. Cr3+ 3. △Ho = 131.3 kJ/mol and △So = 133.6 J/(K·∙mol) for the reaction: C(s) + H2O(g) CO(g) + H2 (g) This reaction will be spontaneous (under standard conditions) at temperatures above: a. 273 C b. 552 C c. 325 C d. 583 C e. 710 C 4. In a voltaic cell, electrons flow from the to the through the . a. anode, cathode, salt bridge b. cathode, salt bridge, wire c. cathode, anode, wire d. cathode, anode, salt bridge e. anode, cathode, wire 5. In the reaction: Co3+ + 6NH3 → Co(NH3)63+ , the Co3+ cation acts as ….. a. a Lewis base b. a Lewis acid c. a coordination complex d. a ligand e. an active metal 6. In a spontaneous process, which of the following always increases? a. the entropy of the system b. the entropy of the surroundings c. the entropy of the universe d. the entropy of the system and the universe e. the entropy of the system, surroundings and the universe 7. What is the charge on the complex anion in Mg(NH4)2[Fe(CN)6] a. -­‐2 b. -­‐3 c. -­‐4 d. +2 e. +4 8. In a biochemical reaction, A + B → C with ΔG°rxn = 30 kJ/mol. Which of the following reactions might be effectively coupled to this reaction so that it becomes more spontaneous? I. C + D → B + E ΔG°rxn = –40 kJ/mol II. C + D → B + E ΔG°rxn = +40 kJ/mol a. I only b. II only c. I or II d. Neither I nor II can increase spontaneity e. No coupling is required as the reaction is already spontaneous 9. Which of the following square-­‐planar complexes would have enantiomers? a. Pt(NH3)42+ b. PtCl42– c. Pt(NH3)2Cl2 d. Pt(NH3)3Cl e. None have enantiomers. 10. If 1 mol of ice melts at its melting point of 273 K, the entropy change for the ice is 22.0 J/K. If the ice melts in someone’s hand at 34°C, what is the change in the entropy of the universe? Assume a final temperature for the water of 0°C. The enthalpy of fusion for ice is 6.01 kJ/mol. a. +19.6 J/K b. –19.6 J/K c. +2.4 J/K d. –2.4 J/K e. +41.5 J/K 11. A 25.00 mL solution of sulfuric acid (H2SO4) was titrated to completion with 34.55 mL of 0.1020 M sodium hydroxide (NaOH). What was the concentration of the sulfuric acid? a. 0.07048 M b. 0.1410 M c. 0.2819 M d. 0.0353 M e. 0.0533 M 12. Which of the following statements is/are correct? A large equilibrium constant means that I. the free-­‐energy change for the reaction is large and negative. II. the free-­‐energy change for the reaction is large and positive. III. the reaction greatly favors formation of the products. IV. only a small amount of product is produced at equilibrium. a. I only b. II only c. both I and III d. both II and IV e. both II and III 13. What is the correct name for the following compound? a. trans-­‐tetramminedichlorochromium(II) b. cis-­‐tetramminedichlorochromium(II) c. cis-­‐triamminedichlorochromium(II) d. cis-­‐tetramminedichlorochromium(III) e. cis-­‐tetramminechlorochromium(II) 14. If 0.0596 mol of Ni are reacted with excess oxygen to form nickel oxide (NiO) under standard state conditions, what is the entropy change for the reaction? 2Ni(s) + O2 ⇄ 2NiO(s) Substance S° (J/mol ·∙ K) Ni 182.1 O2 205.0 NiO 37.99 a. –49.3 J/K b. –24.7 J/K c. –14.7 J/K d. +49.3 J/K e. –10.4 J/K 15. The diagram below represents a voltaic cell. In this cell, the electron flow is from Cd(s)|Cd2+(aq)||Fe3+(aq)|Fe(s) a. Fe to Fe3+ b. Fe to Cd c. Cd to Cd2+ d. Cd2+ to Fe e. Cd to Fe3+ 16. The standard free energy of formation, ΔGf°, of atomic oxygen is 230.1 kJ/mol. Determine the equilibrium constant for the following reaction at standard thermodynamic conditions. O2(g) ⇄ 2O(g) a. 4.7 x 10-­‐41 b. 2.3 x 10-­‐61 c. 2.2 x 10-­‐81 d. 2.1 x 10-­‐40 e. 4.5 x 10-­‐80 17. Which diagram correctly shows the d6 crystal field splitting for the cobalt ion in a high spin [CoF6]3-­‐ complex? a. I b. II c. III d. IV e. None of these are correct 18. In a titration of monoprotic acids and bases, there is a large change in pH a. At the point where pH = pKa of the acid b. When the volume of acid is exactly equal to the volume of base c. When the concentration of acid is exactly equal to the concentration of base d. When the number of moles of acid is exactly equal to the number of moles of base e. At the point where pH = pKb of the base 19. Which of the following is a chelating agent? a. CN-­‐ b. –OOC-­‐COO– c. H2O d. Cl-­‐ e. NH3 20. The three molecules below are examples of… a. Stereoisomers b. Structural Isomers c. Enantiomers d. cis-­‐trans isomers e. they are all the same molecule 21. The correct formula for ammonium tetracyanoplatinate(II) is a. (NH4)2[Pt(CN)6]. b. NH4[Pt(CN)4]. c. (NH3)2[Pt(CN)4]. d. (NH4)2[Pt(CN)4]. e. (NH4)2Pt(CN)4. 22. Given the following standard reduction potentials: Al3+ (aq) + 3e-­‐ → Al(s) Ered = 1.66 V Cd2+ (aq) + 2e-­‐ → Cd(s) Ered = 0.40 V Mg2+ (aq) + 2e-­‐ → Mg(s) Ered = 2.37 V Cr3+ (aq) + 3e-­‐ → Cr(s) Ered = 0.740 V Fe2+ (aq) + 2e-­‐ → Fe(s) Ered = 0.440 V Which of the following reactions occur spontaneously under standard conditions? a. 2Al(s) + 3Mg2+(aq) → 2Al3+(aq) + 3Mg(s) b. Cd(s) + Mg2+(aq) → Cd2+(aq) + Mg(s) c. 3Cd(s) + 2Al3+(aq) → 3Cd2+(aq) + 2Al(s) d. Mg(s) + Cd2+(aq) → Mg2+(aq) + Cd(s) e. 2Cr3+(aq) + 3Fe(s) → 2Cr(s) + 3Fe2+(aq) 23. When a molecule of ethylenediamine (H2NCH2CH2NH2) replaces two molecules of NH3 in Co(NH3)63+, the entropy of the system a. increases. b. decreases. c. remains the same. d. cannot be determined. e. is irrelevant. 24. An electrochemical cell is constructed with a zinc metal anode in contact with a 0.052 M solution of zinc(II) nitrate and a silver cathode in contact with a 0.0042 M solution of silver(I) nitrate. What is the emf of this cell at 5°C? Metal/Metal ion E°red silver/silver(I) +0.799 V zinc/zinc(II) –0.762 V a. 1.656 V b. 1.465 V c. 1.561 V d. 1.370 V e. 1.609 V 25. Given the following data, determine the molar free energy of combustion for propane gas, C3H8. C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g) ΔGf° (C3H8, gas) –23.5 kJ/mol ΔGf° (CO2, gas) –394.4 kJ/mol ΔGf° (H2O, gas) –105.6 kJ/mol a. –1629.1 kJ b. –1582.1 kJ c. –476.5 kJ d. +476.5 kJ e. +1582.1 kJ 26. In each of the following coordination complexes, M represents the central metal ion and L1, L2 and L3 represent three different ligands. Which choices show a pair of stereoisomers? a. i, iii and iv b. i and iii c. ii only d. i only e. ii and iv 27. Which of the following unbalanced half reactions is the only reaction that could take place at the cathode of an electrochemical cell? [HINT – reactions do not need to be balanced for you to answer this question.] a. Br2  2BrO3 b. MnO2  MnO4 c. HSO4  H2SO3 d. NO  HNO2 e. Mn2+  MnO4 28. At what point in the following titration curve for a weak acid being titrated with a strong base is the pH equal to the pKa of the acid? The x-­‐axis scale goes from 0.0 mL to 20.0 mL. The sharp rise is at 10.0 mL. a. 0.0 mL b. 5.0 mL c. 9.0 mL d. 10.0 mL e. 18.0 mL 29. An electrochemical cell is constructed with a zinc metal anode in contact with a 0.052 M solution of zinc nitrate and a silver cathode in contact with a 0.0042 M solution of silver(I) nitrate. What is the value of Q to use in the Nernst equation for this cell? a. 2900 b. 12 c. 8.1 x 10–2 d. 3.4 x 10–4 e. 1.00 30. What is G (in kJ/mol) for a reaction mixture (at 25˚C) in which there is 1.500 atm P2 , 1.600 atm Cl2 , 0.650 atm PCl3 and G˚ = 642.9 kJ/mol for: P2(g) + 3Cl2(g) 2PCl3(g) a. 44.2 b. 649.5 c. 704.4 d. 636.3 e. 3.88 x 103 31. Which is the correct number of valence d electrons associated with the central metal ion in K2[Cu(CN)4]? a. 11 b. 10 c. 9 d. 8 e. 7 32. The entropy change of the surroundings, ΔSsurr, is related to heat transfer q and temperature T by a. –qsys/T = ΔSsurr b. +qsys/T = ΔSsurr c. –qsurr/T = ΔSsurr d. (qsys – qsurr)/T = ΔSsurr e. (qsurr – qsys)/T = ΔSsurr 33. Consider the following electrochemical cell: The standard reduction potential for Cu and Zn are: Cu2+(aq) + 2 e-­‐ → Cu(s) E°red = 0.34 V Zn2+(aq) + 2 e-­‐ → Zn(s) E°red = -­‐0.76 V In this operating electrochemical cell, a. electrons flow toward the Cu and the Cu2+ ions migrate toward the Zn. b. electrons flow toward the Cu and the Zn2+ ions migrate toward the Cu. c. electrons flow toward the Zn and the Cu2+ ions migrate toward the Zn. d. electrons flow toward the Zn and the Zn2+ ions migrate toward the Cu. e. there is no electron flow 34. Boltzmann derived the relationship, S = k ln W where W is the a. number of microstates b. vibrational energy c. kinetic energy d. Wentworth factor e. Work 35. Luke Skywalker found that the batteries for his light-­‐saber were running low. A cryptic inscription on the handle translated roughly into “Four AA dark-­‐side batteries required.” The total voltage produced by the four 1.50 V batteries in series therefore was 6.00 volts. If the cell reaction transfers one electron for each mole of the reactants, what is the Gibbs free-­‐energy change for the redox reaction in each of Luke’s batteries? a. –145 kJ/mol b. +145 kJ/mol c. 869 kJ/mol d. –869 kJ/mol e. +579 kJ/mol 36. How many chelation sites and donor groups does EDTA have? a. 2 b. 10 c. 6 d. 4 e. 5 37. The oxidation of hydrogen by oxygen is one of the most-­‐used reactions in fuel-­‐cell technology. The overall reaction, which is given below, has a ΔG° value of –474 kJ/mol. What is the standard cell potential for this fuel cell? 2H2(g) + O2(g) → 2H2O(l) a. 2.46 V b. 4.91 V c. 1.23 V d. 3.58 V e. 1.50 V 38. If the value of E°cell is 0.59 V for the reaction: Cl2(g) + 2Fe2+(aq) → 2Fe3+(aq) + 2Cl–(aq), what is the value of E°cell for: Cl–(aq) + Fe3+(aq) → Fe2+(aq) + ½Cl2(g)? a. -­‐1.18 V b. -­‐0.59 V c. -­‐0.30 V d. 0.30 V e. 0.59 V 39. The following figures represent distributions of gas molecules between two containers connected by an open tube. In which figure is the entropy of the system maximized? a. b. c. e. 40. The equilibrium concentration of Zn2+(aq) in a solution that is 0.0125 M Zn(NO3)2 and 0.600 M NH3 is . Given: Zn2+(aq) + 4 NH3(aq) ⇄ Zn(NH3)42+(aq) Kf = 2.9 x 109 a. Much greater than 0.0125 M b. Slightly greater than, but still close to 0.0125 M c. Stays the same as 0.0125 M d. Slightly less than, but still close to 0.0125 M e. Much less than 0.0125 M 41. Crystal field theory describes a. how ligands cause the metal d orbitals to have different energies. b. the covalent bonding in transition metal complexes. c. how d orbitals change their shapes when ligands are present. d. how metal s, p, and d orbitals are hybridized to bond with ligands. e. the molecular orbitals that describe the bonding in transition metal complexes. 42. If 15 g of aluminum from an empty soda can could be used as an anode of a battery, how long could it supply a current of 10 amps? (1 A = 1 C/s) a. 45 hr b. 15 hr c. 5.4 hr d. 4.5 hr e. 1.5 hr 43. Which statement does not correctly describe a “dead” battery with a voltage of 0? a. The free-­‐energy change for the reaction now is 0. b. All the reactants have been converted into products. c. The products and reactants now are in equilibrium. d. Q = K e. cell potential = 0 44. A metallic object to be plated with copper is placed in a solution of Cu2+. What mass of copper will be deposited if a current of 0.22 amp (1 amp = 1 C/s) flows through the cell for 5400 seconds? a. 0.38 g b. 0.76 g c. 0.14 g d. 0.19 g e. 0.22 g 45. Consider substances that exist as liquids under standard state conditions. What must be the relationship between the enthalpy and free energy of formation for the liquid and the gaseous form of the substance? (Read as more negative and as less negative.) a. ΔH (l) ΔH (g) and ΔG (l) ΔG (g) b. ΔH (l) ΔH (g) and ΔG (l) ΔG (g) c. ΔH (l) ΔH (g) and ΔG (l) ΔG (g) d. ΔH (l) ΔH (g) and ΔG (l) ΔG (g) e. No strict relationship between these values applies 46. The enthalpy and entropy of vaporization of ethanol are 38.6 kJ/mol and 109.8 J/mol ·∙ K, respectively. What is the boiling point of ethanol? a. 625 K b. 351.5 K c. 276 K d. 897 K e. 78.5 K 47. As the temperature of a reaction with ΔS° 0 is increased, the equilibrium constant a. always increase b. always decreases c. always stays the same d. only increases when ΔH° 0 e. only increases when ΔH 0 48. The change in free energy for a reaction, ΔG, depends on the stoichiometric coefficients used in writing the reaction, but cell potentials, E, do not depend on these coefficients. Which statement accounts for this difference? a. These quantities (ΔG and E) are not related, so this difference is not an issue b. The free-­‐energy change is defined for general reactions, and the electromotive force is defined for electrochemical reactions, so this difference is not an issue c. The difference is not relevant because the units differ: kJ/mol for ΔG, and V for E d. The change in free energy depends on both the reaction and the amount of material reacting, while the cell potential depends only on the cell composition e. The statement is false. ΔG does not depend on the stoichiometric coefficients 49. Consider the titration of 30.0 mL of 0.20 M nitrous acid (HNO2) by adding 0.0500 M aqueous potassium hydroxide (KOH) to it. The pH at the equivalence point is . a. greater than 7 b. equal to 7 c. less than 7 d. cannot be determined without more data (not including Ka and Kb) e. is impossible to predict 50. One difference between a voltaic cell and an electrolytic cell is that in an electrolytic cell . a. E°cell 0 b. An electric current is produced by a chemical reaction c. Oxidation occurs at the cathode d. ΔG 0 e. A nonspontaneous reaction is forced to occur Bonus: 51. Dr. Turnpenny grew up in Oneida, NY, where the very well-­‐known silverware company was once based. He even goes as far to check when he is dining out if the restaurant uses Oneida Silverware. At one restaurant that Dr. Turnpenny was eating at, he discovered that his silverware was very tarnished. He remembered reading that the tarnish (Ag2S) would be removed if you immersed the silverware in a hot solution of baking soda (NaHCO3) in a pan lined with aluminum foil. So he snuck into the kitchen and tried this experiment, and it was successful. He noticed a bit of a rotten egg smell (H2S) being produced. Which one of the following statements cannot represent what might have been happening? Metal/Metal ion E°red silver/silver(I) 0.799 aluminum/aluminum(III) –1.677 a. Al → Al3+ + 3e– b. Ag+ + e– → Ag c. 2HCO3– +S2– → H2S + 2CO32– d. 2HCO3– +Ag2S → H2S + 2CO32– + 2Ag e. The aluminum acts as a reducing agent for the silver(I) in the silver sulfide; then the bicarbonate ion protonates the sulfide ion that is released.