Practice Final CH142, Spring 2012 First here are a group of practice problems on Latimer Diagrams: 1. The Latimer diagram for nitrogen oxides in given below. Is NO stable with respect to disproportionation under standard conditions at 25 C? 0.96 V 0.79 V 1.12 V 1.00 V 1.59 V 1.77 V 0.27 V NO 3 - NO 2 (g) HNO 2 NO N 2 O N 2 NH 4 + 1.25 V 2. The Latimer diagram for manganese in acidic solution is given below at 25 C. Find the standard reduction potential for the reduction of permanganate ion, MnO 4 -, to Mn 2+ from the potentials listed. 0.56 V 2.26 V 0.95 V 1.51 V -1.18 V MnO - 2-4 MnO 4 MnO 2 (s) Mn 3+ Mn 2+ Mn (s) 1.69 V 1.23 V 3. The Latimer diagram for manganese in acidic solution is given below at 25 C. (a). Give the best oxidizing agent under standard conditions. (b). Give the best reducing agent. (c). Is Mn(s) a good oxidizing agent? (d). What are the products of the disproportionation of Mn 3+? 0.56 V 2.26 V 0.95 V 1.51 V -1.18 V MnO - 2-4 MnO 4 MnO 2 (s) Mn 3+ Mn 2+ Mn (s) 1.69 V 1.23 V 4. Given the following standard reduction potentials, construct the Latimer diagram: E r ed (V) BrO 4 + 2H + + 2e BrO 3 + H 2 O 1.745 V BrO 3 + 5H + + 4e HBrO + 2H 2 O 1.49 V BrO 3 + 6H + + 5e ½ Br 2 (l) + 3H 2 O 1.513 V HOBr + H + + e ½ Br 2 (l) + H 2 O 1.584 V Br 2 (l) + 2e - 2Br 1.078 V
Chemistry 142 Final Name Part 1: Answer 6 of the following 7 questions. If you answer more than 7 cross out the problem that you don t wish to have graded. (10 points each) 1. Name the following compounds or supply the formula: (a). KClO 4 (b). sulfurous acid (c). [Al(OH) 4 ] (d). diaquadiamminecobalt(ii) chloride 2. (a). Name a good oxidizing agent (b). Name a good reducing agent (c). Name or draw the structural formula for a good multi-dentate ligand: (d). An element that has several allotropes and name two of the allotropes: 3. (a). Give the balanced chemical reaction for Zn(OH) 2 (s) dissolving in a strong acid: (b). Give the balanced chemical reaction for Zn(OH) 2 (s) dissolving in a strong base: 4. (a). Give the balanced chemical reaction for Fe 3+ acting as an acid: (b). Write a balanced chemical reaction for the disproportionation of hydrogen peroxide: 5. Choose the spontaneous direction for the following aqueous reactions at 298 K: (a). at standard state: Zn (s) + Cr 3+ Zn 2+ + Cr 2+ (s) or Zn 2+ + Cr 2+ (s) Zn (s) + Cr 3+ (b). at 0.10 M concentrations for each species: [Cu(NH 3 ) 4 ] 2+ Cu 2+ + 4 NH 3 or Cu 2+ + 4 NH 3 [Cu(NH 3 ) 4 ] 2+ (c). at 0.10 M concentrations for each species: PO 4 3- + H 2 O HPO 4 2- + OH - or HPO 4 2- + OH - PO 4 3- + H 2 O (d). BaSO 4 (s) with 0.10 M Na 2 SO 4 : BaSO 4 (s) Ba 2+ + SO 4 2 or Ba 2+ + SO 4 2 BaSO 4 (s)
6. Is perchlorate ion a better oxidizing agent in acidic or basic solution? In acidic solution: 1.19 V 1.21 V 1.65 V 1.63 V 1.36 V ClO 4 - ClO 3 - HClO 2 HOCl Cl 2 Cl - 1.47 V In basic solution: 0.36 V 0.35 V 0.65 V 0.40 V 1.36 V ClO - 4 ClO - 3 ClO - 2 OCl - Cl 2 Cl - 0.88 V 7. For solid [Cu(H 2 O) 4 (NH 3 ) 2 ]Cl 2 : (a). The coordination number is: (b). The oxidation state of the metal is: (c). The coordination geometry is : (d). The ions produced in aqueous solution of the compound: Part 2: Answer 4 of the following 5 problems. If you answer more than 4 cross out the problem that you don t wish to have graded. (10 points each) 1. Calculate the standard state cell voltage, standard state reaction Gibbs energy, and equilibrium constant at 25 C for the reaction: Zn (s) + 2 Fe 3+ Zn 2+ + 2 Fe 2+. 2. Calculate the solubility of PbBr 2 in pure water, K sp = 2.1x10-6.
3. Calculate the ph at the equivalence point of a titration of 25.0 ml of 0.100 NaBrO with 0.100 M HCl. K a for HBrO is 2.5x10-9. Show the reaction that determines the ph. 4. Calculate the ph of a solution prepared from 25.0 ml of 0.150 M acetic acid and 25.0 ml of 0.100 M NaOH. K a for acetic acid is 1.8x10-5. 5. For the first-order reaction 2N 2 O 5 2N 2 O 4 + O 2, the activation energy is 106. kj/mol. How many times faster will the reaction go at 100. C than at 25.0 C?
Standard Reduction Potentials at 25 C E r ed (V) F 2 (g) + 2e - 2F - 2.87 H 2 O 2 + 2 H + + 2 e - 2 Η 2 O 1.763 PbO 2 (s) + 4H + + SO 2-4 + 2e - PbSO 4 (s) + 2H 2 O 1.69 MnO - 4 + 8H + + 5e - Mn 2+ + 4H 2 O 1.49 PbO 2 (s) + 4H + + 2e - Pb 2+ + 2H 2 O 1.46 Cl 2 (g) + 2e - 2Cl - 1.36 Cr 2 O 2-7 + 14H + + 6e - 2Cr 3+ + 7H 2 O 1.33 O 2 (g) + 4H + + 4e - 2H 2 O 1.23 Br 2 (g) + 2e - 2Br - 1.078 NO - 3 + 4H + + 3e - NO (g) + 2H 2 O 0.96 Hg 2+ + 2e - Hg (l) 0.85 Ag + + e - Ag (s) 0.80 Fe 3+ + e- Fe 2+ 0.77 O 2 (g) + 2 H + + 2 e - Η 2 O 2 0.695 I 2 (s) + 2e - 2I - 0.54 Cu + + e - Cu (s) 0.52 Cu 2+ + 2e - Cu (s) 0.34 AgCl (s) + 1 e - Ag (s) + Cl - 0.222 Cu 2+ + e - Cu + 0.15 Sn 4+ + 2e - Sn 2+ 0.15 2H + + 2e - H 2 (g) 0.00 Fe 3+ + 3e - Fe (s) -0.04 Pb 2+ + 2e - Pb (s) -0.13 Sn 2+ + 2e - Sn (s) -0.14 Ni 2+ + 2e - Ni (s) -0.25 PbSO 4 (s) + 2e - 2- Pb + SO 4-0.359 Cr 3+ + e - Cr 2+ -0.40 Cd 2+ + 2e - Cd (s) -0.40 Fe 2+ + 2e - Fe (s) -0.41 Cr 3+ + 3e - Cr (s) -0.74 Zn 2+ + 2e - Zn (s) -0.76 V 2+ + 2e - V (s) -1.18 Mn 2+ + 2e - Mn (s) -1.18 Al 3+ + 3e - Al (s) -1.66 Mg 2+ + 2e - Mg (s) -2.37 Na + + e - Na (s) -2.714 Ca 2+ + 2e - Ca (s) -2.866 K + + e - K (s) -2.925 Li + + e - Li (s) -3.045 OCl + H 2 O (l) + 2 e - O 2 (g) + 2 OH +0.890 O 2 (g) + 2 H 2 O (l) + 4 e - 4 ΟΗ +0.401 2H 2 O + 2e - H 2 (g) + 2OH -0.828
Formulas and Constants Given on the ACS Test R = 8.314 J mol -1 K -1 N A = 6.022x10 23 mol -1 R = 0.0821 L atm mol -1 h = 6.626x10-34 J s 1 F = 96,485. C mol -1 c = 2.998x10 10 m s -1 1 F = 96,485. J V -1 mol 0 C = 273.15 K Arrhenius Equation: Nernst Equation: Integrated Rate Laws: k = A e -E a/rt E = E RT nf ln Q zero: [A] = [A] o kt Nernst Equation at 25 C: E = E 0.05916 V log Q n first: ln [A] = ln [A] o k t 1 1 second: = k t + [A] t [A] o Additional Formulas and Constants Given on the Colby Test t ½ = ln 2 k = 0.693 k k = A e -E a/rt 1 t ½ = [A] o k ln k= E a R x = -b ± b2-4ac 2a 1 T + ln A S = nr ln(v 2/V 1 ) ln k T2 = E a k T1 R 1 1 T or ln k T1 = E a 2 T 1 k T2 R 1 1 T 2 T 1 K p = K c (RT) n