CHM 2046 Exam 2 GOWER Sections (Form Code A) Fall 2012 Instructions: On your scantron sheet enter and bubble in your name, UF ID number, and Form Code (see above). You may retain your exam sheet (mark your answers on it for future reference) . Check your scantron bubbling carefully – scantron bubbling errors will not be negotiated.

Notes/Info : All given standard thermodynamic values are at 25°C unless otherwise indicated.R = 8.314 J/mol•K and 0.0821 lit•atm/mol•K 1 F = 96,500 C/mol e– 1V = 1J/C 1A = 1C/s

1. Consider the following equilibrium system at 25°C and select the true statement below:A−(aq) + H2O(l) ↔ HA(aq) + OH−(aq) Kb = 1.0 x 10−4 at 25°C

(1) H2O is a stronger acid than HA (2) A− is a stronger base than OH−

(3) the ΔG° for this system at 25°C is < 0 (4) (Ka of HA) = 1 / (Kb of A−)(5) the pH at the equivalence point of a titration of HA with NaOH will be > 7.00

2. Consider the following reactions and select the true statement below.CO2(g) + H2O(l) → H2CO3(aq) Fe3+(aq) + 6H2O(l) → Fe(H2O)6

3+(aq)(1) these reactions are both Lewis and Brønsted-Lowry acid-base reactions (2) Fe(H2O)6

3+ is both a Lewis acid-base adduct and a Brønsted-Lowry acid(3) the H atoms in H2O form coordinate covalent bonds with the C in CO2

(4) in Fe(H2O)63+ the Fe3+ is attracted to the H2O molecules via ion-dipole intermolecular forces

(5) a 1.0 M aqueous solution of FeCl3 would be predicted to have a pH > 7.00

3. Consider the following equilibrium at 25°C and select the true statement below.N2H4(g) ↔ N2(g) + 2H2(g) ΔH°rxn = ‒95 kJ

(1) Qeq < Keq (2) Keq > 1 (3) ΔS° < 0 (4) ΔG° = 0 (5) N2H4(g) is “thermodynamically stable” at 25°C

4. Calculate ΔG at 25°C for the precipitation of lead(II) chloride from mixing 100. mL of 0.050 M lead(II) nitrate solution with 100. mL of 0.25 M sodium chloride solution.  The ΔG° for the reaction at 25°C = −27.36 kJ/mol.  (Hint: write out reaction equation – also, consider total solution volume)

(1) −13 kJ/mol (2) −7.9 kJ/mol (3) −47 kJ/mol (4) −21 kJ/mol (5) −3.7 kJ/mol

5. Use the following data to estimate the normal boiling point of mercury in °C.(ΔH°f of Hg(g) = 62 kJ/mol; S° of Hg(l) = 76 J/mol•K; S° of Hg(g) = 175 J/mol•K)

(1) 270°C (2) 550°C (3) 460°C (4) 190°C (5) 350°C

6. A saturated solution of Ag2SO4 at 25°C contains 3.1 x 10−2 M Ag+ ions. Determine the ΔG° for the solution at this temperature. (hint: write out the expression for Ksp)

(1) +20 kJ/mol (2) −20 kJ/mol (3) +28 kJ/mol (4) −28 kJ/mol (5) can’t determine without ΔH° and ΔS° data

7. The ΔG° for the decomposition of solid cobalt(II) oxide to cobalt metal and oxygen gas is +214 kJ at 25°C. (ΔH° = +238 kJ/mol; ΔS° = +80.5 J/mol•K) Can standard-state equilibrium be reached at ≤ 800°C? (assume ΔH° and ΔS° do not change with temperature)

(1) no because the temperature would have to be > 800°C for ΔG° = 0 (2) yes because ΔG° < 0 at 800°C (3) yes because Poxygen = 1 atm at ≤ 800°C(4) yes because Keq > 1 at 800°C (5) no - this reaction is not spontaneous at any temperature

8. Nonspontaneous reaction “A” can be thermodynamically coupled with spontaneous reaction “B” to result in spontaneous overall reaction “C” at 25°C if......

(1) (ΔG°A + ΔG°B) > 0 (2) (ΔG°A • ΔG°B) = 0 (3) (ΔG°A + ΔG°B) < 0 (4) (ΔG°A / ΔG°B) > 1 (5) (ΔG°A − ΔG°B) = 0

9. Calculate the pH of a 1.0 M KNO2 solution at 25°C, given the following information.NO2

–(aq) + H2O(l) ↔ HNO2(aq) + OH–(aq)ΔG°rxn = 18 kJ/mol(1) 12.42 (2) 11.58 (3) 9.33 (4) 8.19 (5) 10.72

10. Select the true statement: (1) when Q < K, the system can release no more free energy(2) when ΔG > 0, the system can release free energy (3) when ΔG = 0, ΔG° must also = 0(4) when ΔG > 0, ΔG is the maximum useful work obtainable from the system (5) when ΔG < 0, the system can release free energy until Q = K

11. Consider the following equilibrium system at 25°C. If [Pb2+]eq = 0.045 M and the solution is buffered at pH = 2.00, calculate the pressure of H2 (in atm) required to maintain equilibrium.

Pb(s) + 2H+(aq) ↔ Pb2+(aq) + H2(g)(1) 440 atm (2) 280 atm (3) 120 atm (4) 55 atm (5) 40 atm

12. You have a concentration cell with two Cd electrodes suspended in two separate Cd2+(aq) solutions that are 1.00 M and 1.0 x 10−5 M. Calculate the potential for this cell at 25°C.

(1) –0.15 V (2) 0.15 V (3) –0.06 V (4) 0.06 V (5) –0.40 V

13. Which metal below would make an appropriate metallic container in which to store an aqueous silver nitrate solution?

(1) iron (2) tin (3) copper (4) aluminum (5) none of these metals

14. Based on the following information, estimate the molar solubility of AgBr in water at 25°C. Ag+(aq) + e– → Ag(s) E° = 0.80 VAgBr(s) + e– → Ag(s) + Br–(aq) E° = 0.07 V

(1) 5 x 10–13 M (2) 2 x 10–25 M (3) 2 x 10–15 M (4) 7 x 10–7 M (5) 3 x 10–11 M

15. It took 5.00 minutes for a current of 3.00 amp to plate out 0.274 g of an unknown metal M from a solution containing dissolved M(NO3)2. Identify the metal M.

(1) Zn (2) Sn (3) Ni (4) Ti (5) Cd

16. An aqueous solution of an unknown salt of palladium (Pd) is electrolyzed by a current of 2.50 A passing for 60.0 min. If 4.962 g Pd is produced at the cathode, what is the charge on the palladium ions in solution?

(1) +1 (2) +2 (3) +3 (4) +4 (5) +5

17. An aqueous solution containing the following dissolved salts is electrolyzed. Predict what products are produced at the anode (an) and cathode (cat)? (dissolved salts: MgBr2, NaI, NiSO4)

(1) O2(g) an, Ni(s) cat (2) I2(s) an, Ni(s) cat (3) Br2(l) an, Ni(s) cat (4) O2(g) an, H2(g) cat (5) SO2(g) an, H2(g) cat

18. Select the false statement below:(1) the relatively high potential of the lithium-ion battery is due to lithium being a strong reducer(2) a hydrogen fuel cell utilizes energy from the combustion of H2 gas(3) iron rusts more quickly in contact with ionic solutions(4) rusting of metal A may be inhibited by alloying or coating metal A with a less reactive metal B(5) batteries act as galvanic/voltaic cells during discharge, and as electrolytic cells during recharge

19. Which pair of substances below is properly listed in order of decreasing entropy?(1) CO(g) > CO2(g) (2) CO2(aq) > CO2(g) (3) MgO(s) > BaO(s) (4) NaCl(s) > NaCl(aq) (5) 2N(g) > N2(g)

20. Calculate the cell potential for the following voltaic cell.Cr(s) | Cr3+(0.020 M) || Fe2+(2.0 M) | Fe(s)

(1) 0.34 V (2) 0.32 V (3) 0.26 V (4) 0.17 V (5) 0.38 V

21. Consider the following reaction at 25°C and select the true statement below:2H2O(l) + Mn2+(aq) + 2Fe3+(aq) → 2Fe2+(aq) + MnO2(s) + 4H+(aq)

(1) E° > 0 (2) ΔG° < 0 (3) MnO2 is a stronger oxidizer than Fe3+ (4) Mn2+ is a stronger reducer than Fe2+ (5) the H in H2O is oxidized to H+

22. Consider a concentration cell consisting of two hydrogen electrodes, which can be used to measure pH.  One of the cells is a standard hydrogen electrode (SHE), and the other cell is in contact with an aqueous solution having an unknown pH.  If the unknown [H+] < 1.0 M, then reduction occurs at the SHE and oxidation occurs at the nonstandard hydrogen electrode.  If the measured potential of the cell is 0.189 V, what is the pH of the unknown solution at 25°C?

(1) 7.20 (2) 3.19 (3) 6.39 (4) 1.60 (5) 8.32

23. Consider the following equilibrium at 25°C and select the false statement below.M2+(aq) + 2X−(aq) ↔ MX2(s) ΔG° < 0

(1) when ΔG° = 0, [M+] = [X–] = 1.0 M (2) Ksp of MX2(s) < 1 (3) ΔH° < 0(4) if Qsp/Ksp = 1, then ΔG  = 0 (5) the molar solubility of MX2 is > 1.0 M

24. The endothermic reaction XY2(g) → X(g) + 2Y(g) is:(1) spontaneous at low temperatures (2) spontaneous at high temperatures(3) reactant-favored at high temperatures (4) product-favored at low temperatures(5) not spontaneous or product-favored at any temperature

25. Predict the products of the electrolysis of a molten mixture of KCl and MgBr2.(1) Mg (cat), Br2 (an) (2) K (cat), Cl2 (an) (3) K (cat), Br2 (an) (4) Mg (cat), Cl2 (an) (5) none