1. [7 points] Which element is oxidized in the reaction below? + O 2 + H 2 O

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Silvia Lynne Fisher
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1 1. [7 points] Which element is oxidized in the reaction below? K 2 CrO 4 (aq) + BaCl 2 (aq) BaCrO 4 (s) + 2KCl a. Cl b. Cr c. O d. Ba e. This is not an oxidation-reduction reaction 2. [7 points] What are the coefficients of Cl 2 O 7 and H 2 O, when the following redox equation is balanced in basic solution? H 2 O 2 + Cl 2 O 7 ClO O 2 + H 2 O a. 1, 1 b. 2, 7 c. 1, 5 d. 1, 3 e. None of the above 3. [7 points] What is the coefficient of the hypochlorite ion, ClO -, when the following equation is balanced in basic solution? ClO - + S 2 O 3 2- Cl - + SO 4 2- a. 1 b. 2 c. 3 d. 4 e [7 points] The purpose of a salt bridge in an electrochemical cell is to. a. Maintain electrical neutrality in the half-cells via migration of ions. b. Provide a source of ions to react at the anode and cathode c. Provide oxygen to facilitate oxidation at the anode d. Provide a means for electrons to travel from the anode to the cathode e. Provide a means for electrons to travel from the cathode to the anode

2 5. [7 points] In experiment 25 you added an iron nail to a solution containing tin ions in order to reduce Sn 4+ ions to Sn 2+. In this reaction Fe (s) acts as a reducing agent. Which of the following reagents could be used as an alternative reducing agent, to drive a spontaneous redox reaction (consider the standard reduction potentials found on the back page to answer this question)? (i) FeCl 2 (aq) (ii) AgNO 3 (aq) (iii) H 2 (g) (iv) Cu (s) a. FeCl 2 (aq) b. H 2 (g) c. AgNO 3 (aq) d. AgNO 3 (aq) & H 2 (g) e. Cu (s) & FeCl 2 (aq) 6. [7 points] Consider a voltaic cell where one cell compartment contains Cu(NO 3 ) 2 (aq) in contact with a Cu electrode, while the other cell compartment contains CrCl 3 (aq) in contact with a Cr electrode. Which electrode is the anode and what is the standard cell potential (Eº cell ) for this cell? a. Anode = Copper, Eº cell = V b. Anode = Chromium, Eº cell = V c. Anode = Copper, Eº cell = V d. Anode = Chromium, Eº cell = V e. Anode = Copper, Eº cell = V 7. [7 points] In the above problem what would be the cell potential if the temperature were 298 K, the CrCl 3 concentration was 0.50 M, and the Cu(NO 3 ) 2 concentration was M? a V b V c V d V e. None of the above

3 8. [7 points] Consider a voltaic cell based on the following reaction: 2H + (aq) + Sn (s) Sn 2+ (aq) + H 2 (g) Which of the following actions would increase the measured cell potential? a. Increasing the ph in the cathode compartment b. Increasing the pressure of H 2 gas in the cathode compartment c. Increasing the size of the tin anode d. Decreasing [Sn 2+ ] in the anode compartment e. All of the above actions will increase the cell potential 9. [7 points] What is the value of ΔGº for this reaction (standard reduction potentials are given on the last page)? a. 342 kj b kj c. 515 kj d kj e kj 3Sn 4+ (aq) + 2Cr (s) 2Cr 3+ (aq) + 3Sn 2+ (aq) 10. [7 points] What is the anode in an alkaline battery? a. MnO 2 b. KOH c. Zn powder d. Mn 2 O 3 e. Pt 11. [7 points] How many seconds are required to produce 4.00 g of aluminum metal from the electrolysis of molten AlCl 3 with an electrical current of 12.0 A. a s b s c s d s e s

4 12. [7 points] Calculate the equilibrium constant at 25 ºC for the following reaction: a b. 3.2 c d e. None of the above Fe 2+ (aq) + Ag + (aq) Ag (s) + Fe 3+ (aq) Construct a molecular orbital diagram for carbon monoxides, CO, and use it to answer the following three questions: 13. [7 points] How would you describe the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO): a. HOMO = pi bonding, LUMO = sigma antibonding b. HOMO = pi antibonding, LUMO = sigma antibonding c. HOMO = pi bonding, LUMO = pi antibonding d. HOMO = sigma antibonding, LUMO = pi antibonding e. HOMO = sigma bonding, LUMO = pi bonding 14. [7 points] What is the bond order in CO? a. 1 b. 1.5 c. 2 d. 2.5 e [7 points] If you were to stretch the C-O bond, so that the C-O bond distance increases, how would that impact the HOMO-LUMO energy gap? a. It would increase b. It would decrease c. It would remain unchanged d. It is impossible to know from the information given 16. [7 points] Complexes containing transition metals with which one of the following electron configurations are usually colorless? (a) d 2 (b) d 1 (c) d 5 (d) d 8 (e) d 10

17. [7 points] Which of the following MO s represents an antibonding pi (π * )

[7 points] Given the fact that [Cr(H 2 O) 6 ] 3+ is violet, which of the following

nm, while the CrO 4 2- ion is yellow with an absorption maximum near 400 nm.

5 17. [7 points] Which of the following MO s represents an antibonding pi (π * ) interaction? (a) (b) (c) (d) 18. [7 points] Given the fact that [Cr(H 2 O) 6 ] 3+ is violet, which of the following complex ions is most likely to be green? a. [Cr(NO 2 ) 6 ] 3- b. [CrCl 6 ] 3- c. [Cr(NH 3 ) 6 ] 3+ d. [Cr(CN) 6 ] [7 points] The permanganate ion, MnO 4 -, is purple with an absorption maximum at 565 nm, while the CrO 4 2- ion is yellow with an absorption maximum near 400 nm. What color would you expect for the hypothetical FeO 4 molecule. a. Red b. Green c. Blue d. Orange e. Colorless, because the oxygen to iron charge transfer transition would fall in the UV region of the spectrum.

6 20. [7 points] What electronic transition is responsible for the blue color of a sapphire? a. A d to d transition on a chromium impurity b. A charge transfer from oxygen to aluminum c. A charge transfer transition from oxygen to a d-orbital on a chromium impurity d. A charge transfer from a Fe 2+ ion impurity to a neighboring Ti 4+ ion impurity e. A d to d transition on a cobalt impurity 21. [7 points] How many unpaired electrons are there on a [NiCl 4 ] 2- complex ion with tetrahedral geometry? a. 0 b. 1 c. 2 d. 4 e [7 points] What structure can be described as a cubic close packing of anions with 50% of the tetrahedral holes filled? a. Rock salt b. Nickel Arsenide c. Zinc Blende d. Wurtzite e. Cesium Chloride 23. [7 points] The mineral cinnabar (HgS) adopts the Zinc Blende structure type with a unit cell edge of Å? What is the coordination environment of mercury and of sulfur. a. Hg octahedron, S octahedron b. Hg tetrahedron, S cube c. Hg tetrahedron, S tetrahedron d. Hg tetrahedron, S octahedron e. Hg octahedron, S tetrahedron

7 24. [7 points] Given the information in the previous problem what is the Hg-S bond distance in cinnabar (HgS). a Å b Å c Å d Å e Å 25. [7 points] The strongest peak in the X-ray diffraction pattern of cubic MgO, which adopts the rock salt structure type, is the (111) peak. If the pattern was collected with Cu Ka radiation (wavelength of Å), and the 2-theta location of the (111) peak is 37.0º, what is the length of the unit cell edge, a? a Å b Å c Å d Å e. None of the above

8 Standard Reduction Potentials Half Reaction Eº (V) Cr 3+ (aq) + 3e - Cr (s) Ag + (aq) + e - Ag (s) Fe 2+ (aq) + 2e - Fe (s) Fe 3+ (aq) + e - Fe 2+ (s) Cu 2+ (aq) + 2e - Cu (s) Zn 2+ (aq) + 2e - Zn (s) Pb 2+ (aq) + 2e - Pb (s) Sn 4+ (aq) + 2e - Sn 2+ (aq) Sn 2+ (aq) + 2e - Sn (s) H + (aq) + 2e - H 2 (g) BiO + (aq) + 2H + (aq) + 3 e - Bi (s) + H 2 O Spectrochemical Series Weak Field Cl - < F - < H 2 O < NH 3 < NO - 2 < CN - Strong Field Ligands Ligands Physical Constants & Conversion Factors h = J-s c = m/s R = J/K-mol 1 Å = m 1 ev = J 1 F = 96,500 C/mol = 96,500 J/V-mol 1 A = 1 C/s 1 ev = J

a. Orange b. Green c. Red d. Yellow e. Colorless, because the crystal field splitting is so large that the absorption is shifted into the ultraviolet

1. [6 points] The complex [Ni(NH 3 ) 6 ] 2+ has a blue-violet color. What color would you expect for [Ni(H 2 O) 6 ] 2+? a. Orange b. Green c. Red d. Yellow e. Colorless, because the crystal field splitting