Chemistry 1304.001 Name (please print) Exam 4 (100 points) April 12, 2017 On my honor, I have neither given nor received unauthorized aid on this exam. Signed Date Circle the letters only. NO ANSWERS in the Columns! (3 points each) 1. With respect to the system only, a reaction with H > 0 and S < 0 is predicted to be: a. Spontaneous at all temperatures d. Non-spontaneous at all temperatures b. Spontaneous at high temperatures only e. Indeterminate without values for H and S c. Spontaneous at low temperatures only f. None of these 2. Which one of the following reactions would you expect to have highest S? a. C 2 H 2 (g) + 5 / 2 O 2 (g) 2 CO 2 (g) + H 2 O (g) b. CH 4 (g) + 2 O 2 (g) CO 2 (g) + 2 H 2 O (g) c. C 2 H 4 (g) + 3 O 2 (g) 2 CO 2 (g) + 2 H 2 O (g) d. C 2 H 6 (g) + 7 / 2 O 2 (g) 2 CO 2 (g) + 3 H 2 O (g) e. all have the same S 3. Calculate the concentration of fluoride ions in a saturated barium fluoride (K sp = 1.7 10 6 ) solution. a. 7.6 10-3 M d. 1.5 10-2 M b. 1.7 10-6 M e. 3.4 10-5 M c. 3.4 10-6 M f. none of these 4. Determine the equilibrium constant K p at 25 C for the reaction N 2 (g) + 3 H 2 (g) 2 NH 3 (g) [ G f (NH 3 (g)) = 16.6 kj/mol]. a. 3.4 d. 2.60 b. 8.28 10-2 e. 6.60 10 5 c. 1.52 10-6 f. none of these 5. Calculate E cell for a silver-aluminum cell in which the cell reaction is Al (s) + 3 Ag + (aq) Al 3+ (aq) + 3 Ag (s) a. 2.46 V d. 0.86 V b. 0.86 V e. 0.74 c. 2.46 V f. none of these 6. For the conversion of liquid formic acid, HCOOH, into gaseous formic acid, the H rexn is 47 kj/mole and S is 121 J/mol. What is the boiling point of formic acid? HCOOH (l) a. 274 C d. 0.39 K b. 2.6 x 10-3 C e. 2.6 K c. 115 C f. none of these HCOOH (g) 7. (7 points) Calculate G for the reaction below when [H + ] is 1.0 x 10-5 and [OH ] is 1.0 x 10-6. Show ALL WORK! H 2 O (l) H + (aq) + OH (aq)
8. a. (6 points) Calculate the ph of a solution that is 0.60 M CH 3 COOH and 0.10 M CH 3 COONa. pk a = 4.74. Show ALL REACTIONS and all WORK. page 2 b. (11 points) Will Fe(OH) 3 precipitate from the solution in part a, if the solution is also made to be 0.0010 M in Fe 3+? For Fe(OH) 3, K sp = 6.8 10-36. Show ALL REACTIONS and all WORK. 9. (8 points) Write balanced oxidation and reduction half reactions and the balanced overall reaction for the following which ionic redox equation. The reaction occurs in basic solution. C2O 2-4 + MnO - 4 MnO2 + CO2 Balance reduction half reaction Balanced oxidation half reaction Overall balanced ionic reaction
page 3 10. (15 points) Calculate the temperature at which K p = 4.00 for the reaction below assuming that H and S are independent of temperature. Show ALL WORK N 2 O 4 (g) 2 NO 2 (g). H f (kj/mol) S (J/K mol) NO 2 (g) 33.85 240.46 N 2 O 4 (g) 9.66 304.3 11. (10 points) SHOW ALL WORK. Despite your problems with the last buffer prep, you still have your position as a TA for a Gen Biology lab. Once again, the instructor asks you to make a buffer solution starting with 10.0 L of 3.0 M NaHCO 3 that another TA already made. This time, however, the ph needs to be 10.3. Once again you look around the lab and find only a 2.0 L bottle of concentrated HCl (11.65 M) and 1000 g bottle of solid NaOH (molar mass 40.0 g). Show your calculations/reasoning and appropriate chemical reactions to explain how you would convert the 10.0 L of 3.0 M NaHCO 3 to a buffer with ph of about 10.3. [for H 2 CO 3 : K a1 = 4.2 10-7, K a2 = 4.8 10-11 ]
page 4 12. Calculate the molar solubility of Cu 3 (PO 4 ) 2 in each of the following solutions given that solubility product constant of Cu 3 (PO 4 ) 2 is 1.4 x 10-37 and the formation constant of Cu(CN) 2-4 is 1.0 x 10 29. Show ALL REACTIONS and all WORK for each part a. 1.00 M Na 3 PO 4 (9 points) b. 1.20 M NaCN (16 points) c. (Bonus: 5 points) Calculate the concentration of CN in part b above.
page 5 Some Standard Reduction Potentials E (volts) Cl 2 (g) + 2 e - 2 Cl - (aq) 1.36 Br 2 (g) + 2 e - 2 Br - (aq) 1.07 Ag + (aq) + 1 e - Ag(s) 0.80 Fe 3+ (aq) + e - Fe 2+ (aq) 0.77 O 2 (g) + 4 H + (aq) + 4 e - 2 H 2 O 0.40 Cu 2+ (aq) + 2 e - Cu (s) 0.34 Sn +4 (aq) + 2 e - Sn +2 (aq) +0.13 2 H + (aq) + 2 e - H 2 (s) 0 Pb 2+ (aq) + 2 e - Pb (s) 0.13 Sn +2 (aq) + 2 e - Sn (s) 0.14 Ni +2 (aq) + 2 e - Ni (s) 0.25 Fe 2+ (aq) + 2 e - Fe (s) 0.44 Zn +2 (aq) + 2 e - Zn (s) 0.76 2 H 2 O (l) + 2 e - 2 OH - (aq) + H 2 (g) 0.83 Zn(OH) 2 (s) + 2 e Zn (s) + 2 OH (aq) 1.25 Al 3+ (aq) + 3 e - Al (s) 1.66 Periodic Table of the Elements IA VIIIA (1) (18) 1 2 gas constant (R) 0.082057 L. atm/mol. K 1.0080 (2) 8.314 J/mole. K (13) (14) (15) (16) (17) 4.0026 3 4 speed of light (c) 3.00 x 10 8 m/s 5 6 7 8 9 10 specific heat of water (s) 4.184 J/g. C 6.9410 9.0122 Planck's constant 6.63 x 10-34 J. s 10.811 12.011 14.007 15.999 18.998 20.179 1 H IIA IIIA IVA VA VIA VIIA He 2 Li Be B C N O F Ne 11 12 13 14 15 16 17 18 3 Na Mg IIIB IVB VB VIB VIIB........ VIIIB........ IB IIB Al Si P S Cl Ar 22.990 24.305 (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) 26.982 28.086 30.974 32.066 35.453 39.948 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 4 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 39.098 40.078 44.956 47.880 50.942 51.996 54.938 55.847 58.933 58.690 63.546 65.380 69.723 72.610 74.922 78.960 79.904 83.800 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 5 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 85.468 87.620 88.906 91.224 92.906 95.940 98.907 101.07 102.91 106.42 107.87 112.41 114.82 118.71 121.75 127.60 126.90 131.29 55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 6 Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 132.91 137.33 138.91 178.49 180.95 183.85 186.21 190.20 192.22 195.09 196.97 200.59 204.38 207.20 208.98 208.98 209.99 222.02 87 88 89 104 105 106 107 7 Fr Ra Ac Unq Unp Unh Uns 223.02 226.03 227.03 261.11 262.11 263.12 262.12 58 59 60 61 62 63 64 65 66 67 68 69 70 71 Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 140.12 140.91 144.24 145.91 150.36 151.97 157.25 158.93 162.50 164.93 167.26 168.93 173.04 174.97 90 91 92 93 94 95 96 97 98 99 100 101 102 103 Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr 232.04 231.04 238.03 237.05 244.06 243.06 247.07 247.07 242.06 252.08 257.10 258.10 259.10 260.11
Chemistry 1304.001 Name (please print) Exam 4 (100 points) April 12, 2017 On my honor, I have neither given nor received unauthorized aid on this exam. Signed Date Circle the letters only. NO ANSWERS in the Columns! (3 points each) 1. With respect to the system only, a reaction with H > 0 and S < 0 is predicted to be: a. Spontaneous at all temperatures d. Non-spontaneous at all temperatures b. Spontaneous at high temperatures only e. Indeterminate without values for H and S c. Spontaneous at low temperatures only f. None of these 2. Which one of the following reactions would you expect to have highest S? a. C 2 H 2 (g) + 5 / 2 O 2 (g) 2 CO 2 (g) + H 2 O (g) b. CH 4 (g) + 2 O 2 (g) CO 2 (g) + 2 H 2 O (g) c. C 2 H 4 (g) + 3 O 2 (g) 2 CO 2 (g) + 2 H 2 O (g) d. C 2 H 6 (g) + 7 / 2 O 2 (g) 2 CO 2 (g) + 3 H 2 O (g) e. all have the same S 3. Calculate the concentration of fluoride ions in a saturated barium fluoride (K sp = 1.7 10 6 ) solution. a. 7.6 10-3 M d. 1.5 10-2 M b. 1.7 10-6 M e. 3.4 10-5 M c. 3.4 10-6 M f. none of these 4. Determine the equilibrium constant K p at 25 C for the reaction N 2 (g) + 3 H 2 (g) 2 NH 3 (g) [ G f (NH 3 (g)) = 16.6 kj/mol]. a. 3.4 d. 2.60 b. 8.28 10-2 e. 6.60 10 5 c. 1.52 10-6 f. none of these 5. Calculate E cell for a silver-aluminum cell in which the cell reaction is Al (s) + 3 Ag + (aq) Al 3+ (aq) + 3 Ag (s) a. 2.46 V d. 0.86 V b. 0.86 V e. 0.74 c. 2.46 V f. none of these 6. For the conversion of liquid formic acid, HCOOH, into gaseous formic acid, the H rexn is 47 kj/mole and S is 121 kj/mol. What is the boiling point of formic acid? HCOOH (l) a. 274 C d. 0.39 K b. 2.6 x 10-3 C e. 2.6 K c. 115 C f. none of these HCOOH (g) 7. (7 points) Calculate G for the reaction below when [H + ] is 1.0 x 10-5 and [OH ] is 1.0 x 10-6. Show ALL WORK! H 2 O (l) H + (aq) + OH (aq)
8. a. (6 points) Calculate the ph of a solution that is 0.60 M CH 3 COOH and 0.10 M CH 3 COONa. pk a = 4.74. Show ALL REACTIONS and all WORK. page 2 9. b. (11 points) Will Fe(OH) 3 precipitate from the solution in part a, if the solution is also made to be 0.001 M in Fe 3+? For Fe(OH) 3, K sp = 6.8 10-36. Show ALL REACTIONS and all WORK. 10. (8 points) Write balanced oxidation and reduction half reactions and the balanced overall reaction for the following which ionic redox equation. The reaction occurs in basic solution. C2O 2-4 + MnO - 4 MnO2(s) + CO2 Balance reduction half reaction Balanced oxidation half reaction Overall balanced ionic reaction
page 3 11. (15 points) Calculate the temperature at which K p = 4.00 for the reaction below assuming that H and S are independent of temperature. Show ALL WORK N 2 O 4 (g) 2 NO 2 (g). H f (kj/mol) S (J/K mol) NO 2 (g) 33.85 240.46 N 2 O 4 (g) 9.66 304.3 12. (10 points) SHOW ALL WORK. Despite your problems with the last buffer prep, you still have your position as a TA for a Gen Biology lab. Once again, the instructor asks you to make a buffer solution starting with 10.0 L of 3.0 M NaHCO 3 that another TA already made. This time, however, the ph needs to be 10.3. Once again you look around the lab and find only a 2.0 L bottle of concentrated HCl (11.65 M) and 1000 g bottle of solid NaOH (molar mass 40.0 g). Show your calculations and appropriate chemical reactions to explain how you would convert the 10.0 L of 3.0 M NaHCO 3 to a buffer with ph of about 10.3. [for H 2 CO 3 : K a1 = 4.2 10-7, K a2 = 4.8 10-11 ]
page 4 13. Calculate the molar solubility of Cu 3 (PO 4 ) 2 in each of the following solutions given that solubility product constant of Cu 3 (PO 4 ) 2 is 1.4 x 10-37 and the formation constant of Cu(CN) 2-4 is 1.0 x 10 29. Show ALL REACTIONS and all WORK for each part a. 1.00 M Na 3 PO 4 (9 points) b. 1.20 M NaCN (16 points) c. (Bonus: 5 points) Calculate the concentration of CN in part b above.