Chem 152 Midterm 2 (Sample) Section:______________ Name:_________________ Note that equations that you will be provided with appear at the end of the exam. Page 1 1. Multiple Choice (4 pts. each): a. For an electrochemical cell to be galvanic, what must be true: A. Ecell < 0 B. ΔG < 0 C. K=1 D. n = 2 b. The potential of interaction between an electron and which of the following species will be greatest in magnitude for the following: A. H B. He+ C. Li+2 D. He c. The electron configuration 1s22s22p63s23p64s23d5 corresponds to: A: Tc B: Mn C: Fe D: Cr d. Which element has the electronic structure [Ar]4s23d6: A: V B: Cr C: Fe D: Ru e. The workfunction of Nb is 6.67 x 10-19 J. This corresponds to which of the following wavelengths: A. 459 nm B. 287 nm C. 298 nm Page 2 D. 320 nm Multiple choice (cont.) f. No currently known element contains electrons in “g orbitals,” but we may find such elements one day. How many electrons can be incorporated into a set of g orbitals: A: 10 B: 14 C: 18 D: 20 g. Which of the following is not an allowed set of quantum numbers for the H atom (given in the form {n, l, ml}): A: {3, 1, 1} B: {2, 0, 0} C: {0, 0, 0} D: {1, 0, 0} h. What is the ionization energy for the H atom? A: 5.3x106 J/mol C: 2.6x106 J/mol B: 1.3x106 J/mol D: 2.1x106 J/mol j. If n = 3 and l = 2, how many ml levels are there: A: 1 B: 3 C: 5 D: 10 k. Sodium losing an electron is a ____________ process, and fluorine losing an electron is a ____________ process. A: B: C: D: endothermic, exothermic endothermic, endothermic exothermic, endothermic exothermic, exothermic Page 3 Section II: Long-Answer/Numerical Questions 2 (20 pts.) Lewis Dot Structures. Write the Lewis dot structures for the following compounds. Include all structural isomers, resonance structures, and formal charges for each structure. Underline the one you believe is the most-reasonable structure. Finally, using VESPR describe the 3D geometry of your mostreasonable structure. An example is provided below: Ex: O3 geometry __________________. a) BrO2 - geometry __________________. b) SF4 geometry __________________. c) ONF geometry __________________. Page 4 3 (10 pts.) What wavelength of light corresponds to electron relaxation from n = 4 to n = 1 in Li+2? Page 5 4. A proposed fuel cell involves the following reaction: 1 CO(g) + O2 (g) → CO2 (g) 2 Given the standard thermodynamic data below, determine the half-cell potential for the oxidation of CO(g) in aqueous media. € Compound CO(g) CO2(g) O2(g) ΔH°f (kJ/mol) -110.52 -393.51 0 (stable elemental form) Page 6 S° (J/mol.K) 197.56 213.63 205.03 More room for problem 4 Page 7 5a. Consider the following electrochemical cell: Cr(s) Cr +3 (aq) NO3− (aq) NO(g) (with a Pt electrode) Write a balanced reaction for the above reaction occurring in acidic solution and determine the cell potential. Page 8 5b. A precipitating reagent is added to the anode side of the electrochemical cell and the cell potential increases to 1.9 V. Determine the concentration of the original ionic anode species after the addition of the precipitating reagent. Page 9 Standard Electrode (Half-Cell) Potentials (298 K) Skeletal Half Reaction (as Reduction)* E° (V) Co+3 (aq)/Co+2 (aq) Au+3(aq)/Au(s) O2(g)/H2O(l) Br2 (l)/ 2Br- (aq) NO3- (aq)/NO (g) NO3- (aq)/N2O4 (g) Ag+ (ag)/Ag (s) O2(g)/OH-(aq) Cu+2 (aq)/Cu (s) 2H+ (aq)/H2 (g) Sn+2 (aq)/Sn (s) Cd+2 (aq)/Cd (s) Fe+2 (aq)/Fe (s) Cr+3 (aq)/Cr (s) Zn+2 (aq)/Zn (s) Mg+2 (aq)/Mg (s) Na+ (aq)/Na (s) +1.82 +1.50 +1.23 +1.07 +0.96 +0.83 +0.80 +0.40 +0.34 0.00 -0.14 -0.40 -0.44 -0.74 -0.76 -1.18 -2.71 *All reactions are written as reductions. Water/H+/OH-/e- needed to create a balanced half-cell reaction are suppressed. Page 10 Useful Information Constants: h = 6.626x10-34 J.s c = 3 x 108 m/s F = 96,485 C/mol ee- charge = 1.6 x 10-19 C e- mass = 9.1 x 10-31 kg R = 8.314 J/mol.K = 0.0821 l.atm/mol.K 1 nm = 10-9 m E = −2.178x10 −18  Z2  J 2  n  n 2h 2 E= 8mL2 o E cell = E cell − o ΔG° = −nFE cell = −RT lnK € ΔG = ΔG° + RT ln(Q) € € c € → € aA + bB ←   cC + dD € E = hν = 0.0591V log(Q) n d [C ] [ D] K= a b A B [ ][ ] 1 meν 2 = hν photon − Φ 2 € € −(Ze)(e) V (r) = r € Δx • Δp = h 4π For H-atom like wavefunctions (l = “el”, not one): € n = 1, 2, …., l = (n-1), (n-2), …. 0, ml = -l……0……l, ms = ± 1/2 € Page 11 hc λ