1A03-2020-Exam review-E4 answers

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3 Chem 1A03 ©2008 – 2020 McMaster University Electrochemistry 1 What is the oxidation state of boron in B 2 O 3 ? A. -2 B. +2 C. +1 D. -3 E. +3 B 2 O 3 Each oxygen atom has a oxidation number of -2. Total = -6 Since molecule is neutral, each Boron must have an oxidation number of +3

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4 Chem 1A03 ©2008 – 2020 McMaster University Electrochemistry 2 Which one of the following reactions is NOT an oxidation-reduction reaction? A. H 2 (g) + Cl 2 (g) → 2 HCl (g) B. SO 3 (g) + H 2 O (l) → H 2 SO 4 (aq) C. Cl 2 (aq) + H 2 O (l) → HCl ( aq) + HOCl (aq) D. 2 Al (s) + Fe 2 O 3 (s) → A1 2 O 3 (s) + 2 Fe (s) E. 3 C (graphite) + 2 KClO 3 (s)→ 3 CO 2 (g) + 2 KCl (s)

5 Chem 1A03 ©2008 – 2020 McMaster University Electrochemistry 2 Which one of the following reactions is NOT an oxidation-reduction reaction? A. H 2 (g) + Cl 2 (g) → 2 HCl (g) B. SO 3 (g) + H 2 O (l) → H 2 SO 4 (aq) C. Cl 2 (aq) + H 2 O (l) → HCl ( aq) + HOCl (aq) D. 2 Al (s) + Fe 2 O 3 (s) → A1 2 O 3 (s) + 2 Fe (s) E. 3 C (graphite) + 2 KClO 3 (s)→ 3 CO 2 (g) + 2 KCl (s)

6 Chem 1A03 ©2008 – 2020 McMaster University Electrochemistry 3 When the following redox reaction is balanced in basic solution, what is the coefficient in front of hydroxide ? A. 2 B. 3 C. 4 D. 6 E. 1 NH 3 (aq) + OCl − (aq ) → Cl 2 (g) + N 2 H 4 (aq) Balanced Red: 2 OCl - + 2e - + 4H + → Cl 2 + 2H 2 O Balanced Ox: 2NH 3 → N 2 H 4 + 2e - + 2H + Combined in acid: 2OCl - + 2H + + 2NH 3 → N 2 H 4 + Cl 2 + 2H 2 O Basic solution: 2OCl - + 2NH 3 → N 2 H 4 + Cl 2 + 2OH -

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7 Chem 1A03 ©2008 – 2020 McMaster University Electrochemistry 3 When the following redox reaction is balanced in basic solution, what is the coefficient in front of hydroxide ? A. 2 B. 3 C. 4 D. 6 E. 1 NH 3 (aq) + OCl − (aq ) → Cl 2 (g) + N 2 H 4 (aq) Balanced Red: 2 OCl - + 2e - + 4H + → Cl 2 + 2H 2 O Balanced Ox: 2NH 3 → N 2 H 4 + 2e - + 2H + Combined in acid: 2OCl - + 2H + + 2NH 3 → N 2 H 4 + Cl 2 + 2H 2 O Basic solution: 2OCl - + 2NH 3 → N 2 H 4 + Cl 2 + 2OH -

8 Chem 1A03 ©2008 – 2020 McMaster University Electrochemistry 4 Given the following standard reduction potentials, select the correct cell diagram for the voltaic (spontaneous) cell. Co 3+ (aq) + e – → Co 2+ (aq) E o red = +1.82 V Ag + (aq) + e – → Ag(s) E o red = +0.80 V A. Ag(s)  Ag + (aq, 1 M)||Co 3+ (aq), Co 2+ (aq, 1M)  Pt(s) B. Ag(s)  Ag + (aq, 1 M)|| Co 2+ (aq)  Pt(s)  Co 3+ (aq, 1M) C. Pt(s)  Co 2+ (aq), Co 3+ (aq, 1M)||3 Ag + (aq, 1 M)  3 Ag(s) D. Pt(s)  Co 2+ (aq), Co 3+ (aq, 1M)||Ag + (aq, 1 M)  Ag(s) E. Ag(s)  Ag + (aq, 1 M)|| Pt(s)  Co 2+ (aq), Co 3+ (aq, 1M)

9 Chem 1A03 ©2008 – 2020 McMaster University Electrochemistry 4 Given the following standard reduction potentials, select the correct cell diagram for the voltaic (spontaneous) cell. Co 3+ (aq) + e – → Co 2+ (aq) E o red = +1.82 V Ag + (aq) + e – → Ag(s) E o red = +0.80 V A. Ag(s)  Ag + (aq, 1 M)||Co 3+ (aq), Co 2+ (aq, 1M)  Pt(s) B. Ag(s)  Ag + (aq, 1 M)|| Co 2+ (aq)  Pt(s)  Co 3+ (aq, 1M) → Pt electrode in wrong spot C. Pt(s)  Co 2+ (aq), Co 3+ (aq, 1M)||3 Ag + (aq, 1 M)  3 Ag(s) → non-spontaneous process D. Pt(s)  Co 2+ (aq), Co 3+ (aq, 1M)||Ag + (aq, 1 M)  Ag(s) → non-spontaneous process E. Ag(s)  Ag + (aq, 1 M)|| Pt(s)  Co 2+ (aq), Co 3+ (aq, 1M) → Pt electrode in wrong spot

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10 Chem 1A03 ©2008 – 2020 McMaster University Electrochemistry 5 Given the following reduction potentials, what species, either reactant or product, has the greatest tendency to be oxidized ? S(s) + 2H + + 2e − → H 2 S (g) E o = +0.144 V O 2 (g) + 4H + + 4e − → 2 H 2 O (l) E o = +1.229 V Mg 2+ (aq) + 2e − → Mg(s) E° = - 2.356 V A. Mg 2+ (aq) B. Mg(s) C. O 2 (g) D. H 2 O(l) E. S(s)

11 Chem 1A03 ©2008 – 2020 McMaster University Electrochemistry 5 Given the following reduction potentials, what species, either reactant or product, has the greatest tendency to be oxidized ? S(s) + 2H + + 2e − → H 2 S (g) E o = +0.144 V O 2 (g) + 4H + + 4e − → 2 H 2 O (l) E o = +1.229 V Mg 2+ (aq) + 2e − → Mg(s) E° = - 2.356 V A. Mg 2+ (aq) B. Mg(s) C. O 2 (g) D. H 2 O(l) E. S(s) Reduction potentials above -> most positive = species with greatest tendency to get reduced. To determine species with greatest tendency to be oxidized, flip to oxidation potentials, and determine most positive value. Mg wants to be oxidized with a E ox of +2.356 V

12 Chem 1A03 ©2008 – 2020 McMaster University Electrochemistry 6 Given the following half reactions, calculate the standard cell potential (in V) for the spontaneous cell reaction. MnO 4 – (aq) + 8 H + (aq) + 5 e – → Mn 2+ (aq) + 4 H 2 O(l) E o red = +1.51 V Pb 2+ (aq) + 2 e – → Pb(s) E o red = – 0.13 V A. +2.37 V B. -1.64 V C. +1.38 V D. -1.38 V E. +1.64 V

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13 Chem 1A03 ©2008 – 2020 McMaster University Electrochemistry 6 Given the following half reactions, calculate the standard cell potential (in V) for the spontaneous cell reaction. MnO 4 – (aq) + 8 H + (aq) + 5 e – → Mn 2+ (aq) + 4 H 2 O(l) E o red = +1.51 V Pb 2+ (aq) + 2 e – → Pb(s) E o red = – 0.13 V A. +2.37 V B. -1.64 V C. +1.38 V D. -1.38 V E. +1.64 V

14 Chem 1A03 ©2008 – 2020 McMaster University Electrochemistry 7 A concentration cell is used to measure the concentration of Zn 2+ in a saturated solution of ZnCO 3 . The saturated solution is at the anode, while there is a 1.0 mol L – 1 solution of Zn(NO 3 ) 2 at the cathode. If the measured voltage of the cell is 0.321 V at 298 K, what is the molar solubility of ZnCO 3 at 298 K in mol L – 1 ? A. 3.6 x 10 -12 B. 7.8 x 10 -12 C. 2.1 x 10 -10 D. 1.4 x 10 -11 E. 5.1 x 10 -9

15 Chem 1A03 ©2008 – 2020 McMaster University Electrochemistry 7 A concentration cell is used to measure the concentration of Zn 2+ in a saturated solution of ZnCO 3 . The saturated solution is at the anode, while there is a 1.0 mol L – 1 solution of Zn(NO 3 ) 2 at the cathode. If the measured voltage of the cell is 0.321 V at 298 K, what is the molar solubility of ZnCO 3 at 298 K in mol L – 1 ? A. 3.6 x 10 -12 B. 7.8 x 10 -12 C. 2.1 x 10 -10 D. 1.4 x 10 -11 E. 5.1 x 10 -9

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16 Chem 1A03 ©2008 – 2020 McMaster University Electrochemistry 7 A concentration cell is used to measure the concentration of Zn 2+ in a saturated solution of ZnCO 3 . The saturated solution is at the anode, while there is a 1.0 mol L – 1 solution of Zn(NO 3 ) 2 at the cathode. If the measured voltage of the cell is 0.321 V at 298 K, what is the molar solubility of ZnCO 3 at 298 K in mol L – 1 ? A. 3.6 x 10 -12 B. 7.8 x 10 -12 C. 2.1 x 10 -10 D. 1.4 x 10 -11 E. 5.1 x 10 -9

17 Chem 1A03 ©2008 – 2020 McMaster University Electrochemistry 8 What is D G (in kJ) for the spontaneous cell produced from the following equations using lowest integer values: Al 3+ (aq) + 3e - → Al(s) E red = -1.676 V Cd 2+ (aq) + 2e - → Cd(s) E red = -0.403 V A. -215 B. +364 C. -737 D. -621 E. +849

18 Chem 1A03 ©2008 – 2020 McMaster University Electrochemistry 8 What is D G (in kJ) for the spontaneous cell produced from the following equations using lowest integer values: Al 3+ (aq) + 3e - → Al(s) E red = -1.676 V Cd 2+ (aq) + 2e - → Cd(s) E red = -0.403 V A. -215 B. +364 C. -737 D. -621 E. +849 E° cell = E° cathode - E° anode E° cell = -0.403 – (-1.676) = +1.273 ∆ G° cell = -nFE° cell ∆ G° cell = -(6)(96485)(1.273) = -737 kJ

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19 Chem 1A03 ©2008 – 2020 McMaster University Electrochemistry 9 A Chemistry 1A03 student assembles an electrochemical cell based on the Cl 2 (g) | 2 Cl − (aq) and Pb 2+ (aq) | Pb (s) half reactions. When operated with all reagents under standard state conditions, she measures a cell voltage of 1.485 V at 298 K. What is the equilibrium constant for the reaction, when it is written to have the lowest whole number coefficients? A. 52 B. 1.5 x10 50 C. 4.3 x10 12 D. 3.1 x10 32 E. 6.3 x10 4

20 Chem 1A03 ©2008 – 2020 McMaster University Electrochemistry 9 A Chemistry 1A03 student assembles an electrochemical cell based on the Cl 2 (g) | 2 Cl − (aq) and Pb 2+ (aq) | Pb (s) half reactions. When operated with all reagents under standard state conditions, she measures a cell voltage of 1.485 V at 298 K. What is the equilibrium constant for the reaction, when it is written to have the lowest whole number coefficients? A. 52 B. 1.5 x10 50 C. 4.3 x10 12 D. 3.1 x10 32 E. 6.3 x10 4 E° cell = (0.0591 V/n)(logK) 1.485V = (0.0591V/2)(log K) 50.254 = logK K = 1.8 x 10 50 ≈ 1.5 x 10 50

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24 Chem 1A03 ©2008 – 2020 McMaster University IMF 2 Which of the following would have the highest melting point? Strongest IMFs = highest melting point A. NH 3 (H bonding) B. SiH 4 (Dispersion Forces) C. CH 4 (Dispersion Forces) D. AsH 3 ( Dipole dipole Forces)

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25 Chem 1A03 ©2008 – 2020 McMaster University IMF 3 What would the dominant intermolecular force be in a pure sample of SF 6 (l)? A. Dipole-Dipole interactions B. Ion-Dipole interactions C. Dispersion forces D. Hydrogen Bonding

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26 Chem 1A03 ©2008 – 2020 McMaster University IMF 3 What would the dominant intermolecular force be in a pure sample of SF 6 (l)? A. Dipole-Dipole interactions B. Ion-Dipole interactions C. Dispersion forces → non-polar molecule D. Hydrogen Bonding

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