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- What is the difference between a battery and a fuel cell?
Problem 82
Problem 82b
(b) Can the “fuel” of a fuel cell be a solid?
- (a) Write the anode and cathode reactions that cause the corrosion of iron metal to aqueous iron(II).
Problem 83
- (b) When the Statue of Liberty was refurbished, Teflon spacers were placed between the iron skeleton and the copper metal on the surface of the statue. What role do these spacers play?
Problem 84
- (a) Magnesium metal is used as a sacrificial anode to protect underground pipes from corrosion. Why is the magnesium referred to as a “sacrificial anode”? (b) Looking in Appendix E, suggest what metal the underground pipes could be made from in order for magnesium to be successful as a sacrificial anode.
Problem 85
- An iron object is plated with a coating of cobalt to protect against corrosion. Does the cobalt protect the iron by cathodic protection?
Problem 86
Problem 87a,b,c
Iron corrodes to produce rust, Fe2O3, but other corrosion products that can form are Fe(O)(OH), iron oxyhydroxide, and magnetite, Fe3O4. (a) What is the oxidation number of Fe in iron oxyhydroxide, assuming oxygen's oxidation number is -2? (b) The oxidation number for Fe in magnetite was controversial for a long time. If we assume that oxygen’s oxidation number is - 2, and Fe has a unique oxidation number, what is the oxidation number for Fe in magnetite? (O)(OH), iron oxyhydroxide, and magnetite, Fe3O4. (c) It turns out that there are two different kinds of Fe in magnetite that have different oxidation numbers. Suggest what these oxidation numbers are and what their relative stoichiometry must be, assuming oxygen’s oxidation number is -2.
Problem 88a
Copper corrodes to cuprous oxide, Cu2O, or cupric oxide, CuO, depending on environmental conditions. (a) What is the oxidation state of copper in cuprous oxide?
Problem 88c,d
Copper corrodes to cuprous oxide, Cu2O, or cupric oxide, CuO, depending on environmental conditions. (c) Copper peroxide is another oxidation product of elemental copper. Suggest a formula for copper peroxide based on its name. (d) Copper(III) oxide is another unusual oxidation product of elemental copper. Suggest a chemical formula for copper(III) oxide.
- (a) What is electrolysis? (b) Are electrolysis reactions thermodynamically spontaneous?
Problem 89
Problem 89c
(c) What process occurs at the anode in the electrolysis of molten NaCl?
Problem 89d
(d) Why is sodium metal not obtained when an aqueous solution of NaCl undergoes electrolysis?
Problem 90d
(d) Why are active metals such as Al obtained by electrolysis using molten salts rather than aqueous solutions?
Problem 91a
(a) A Cr3+(aq) solution is electrolyzed, using a current of 7.60 A. What mass of Cr(s) is plated out after 2.00 days?
Problem 91b
(b) What amperage is required to plate out 0.250 mol Cr from a Cr3+ solution in a period of 8.00 h?
- Metallic magnesium can be made by the electrolysis of molten MgCl2. (a) What mass of Mg is formed by passing a current of 4.55 A through molten MgCl2 for 4.50 days? (b) How many minutes are needed to plate out 25.00 g Mg from molten MgCl2 using 3.50 A of current?
Problem 92
Problem 93
(a) Calculate the mass of Li formed by electrolysis of molten LiCl by a current of 7.5 × 104 A flowing for a period of 24 h. Assume the electrolytic cell is 85% efficient. (b) What is the minimum voltage required to drive the reaction?
- Elemental calcium is produced by the electrolysis of molten CaCl2. (a) What mass of calcium can be produced by this process if a current of 7.5 * 10^3 A is applied for 48 h? Assume that the electrolytic cell is 68% efficient. (b) What is the minimum voltage needed to cause the electrolysis?
Problem 94
- Metallic gold is collected from below the anode when a mixture of copper and gold metals is refined by electrolysis. Explain this behavior.
Problem 95
- A mixture of copper and gold metals that is subjected to electrorefining contains tellurium as an impurity. The standard reduction potential between tellurium and its lowest common oxidation state, Te4+, is Te4+1aq2 + 4 e- ¡ Te1s2 E°red = 0.57 V Given this information, describe the probable fate of tellurium impurities during electrorefining. Do the impurities fall to the bottom of the refining bath, unchanged, as copper is oxidized, or do they go into solution as ions? If they go into solution, do they plate out on the cathode?
Problem 96
- Complete and balance the following disproportionation reactions: (a) Ni⁺(aq) → Ni²⁺(aq) + Ni(s) (acidic solution) (c) H₂SO₃(aq) → S(s) + HSO₄⁻(aq) (acidic solution) (d) Cl₂(aq) → Cl⁻(aq) + ClO⁻(aq) (basic solution)
Problem 97
Problem 97b
A disproportionation reaction is an oxidation–reduction reaction in which the same substance is oxidized and reduced. Complete and balance the following disproportionation reactions:
(b) MnO42-(aq) → MnO4-(aq) + MnO2(s) (acidic solution)
- A common shorthand way to represent a voltaic cell is anode | anode solution || cathode solution | cathode. A double vertical line represents a salt bridge or a porous barrier. A single vertical line represents a change in phase, such as from solid to solution. (a) Write the half-reactions and overall cell reaction represented by Fe | Fe2+ || Ag+ | Ag; calculate the standard cell emf using data in Appendix E. (b) Write the half-reactions and overall cell reaction represented by Zn | Zn2+ || H+ | H2; calculate the standard cell emf using data in Appendix E and use Pt for the hydrogen electrode. (c) Using the notation just described, represent a cell based on the following reaction: ClO3^-_(aq) + 3 Cu_(s) + 6 H+_(aq) -> Cl^-_(aq) + 3 Cu2+_(aq) + 3 H2O_(l); Pt is used as an inert electrode in contact with the ClO3^- and Cl^-. Calculate the standard cell emf given: ClO3^-_(aq) + 6 H+_(aq) + 6 e^- -> Cl^-_(aq) + 3 H2O_(l); E° = 1.45 V.
Problem 98
Problem 99
Predict whether the following reactions will be spontaneous in acidic solution under standard conditions: (a) oxidation of Sn to Sn2+ by I2 (to form I-), (b) reduction of Ni2+ to Ni by I- (to form I2), (c) reduction of Ce4+ to Ce3+ by H2O2, (d) reduction of Cu2+ to Cu by Sn2+ (to form Sn4+).
Problem 100c
Gold exists in two common positive oxidation states, +1 and +3. The standard reduction potentials for these oxidation states are Au+1aq2 + e- ¡ Au1s2 Ered ° = +1.69 V Au3+1aq2 + 3 e- ¡ Au1s2 Ered ° = +1.50 V (c) Miners obtain gold by soaking gold-containing ores in an aqueous solution of sodium cyanide. A very soluble complex ion of gold forms in the aqueous solution because of the redox reaction 4 Au1s2 + 8 NaCN1aq2 + 2 H2O1l2 + O21g2 ¡ 4 Na3Au1CN2241aq2 + 4 NaOH1aq2 What is being oxidized, and what is being reduced in this reaction?
- A voltaic cell is constructed from an Ni2+(aq) / Ni(s) half-cell and an Ag+(aq) / Ag(s) half-cell. The initial concentration of Ni2+(aq) in the Ni2+ - Ni half-cell is [Ni2+] = 0.0100 M. The initial cell voltage is +1.12 V. (a) By using data in Appendix E, calculate the standard emf of this voltaic cell.
Problem 101
- Will the concentration of Ni2+ in the Ni2+ - Ni half-cell increase or decrease as the cell operates?
Problem 101
Problem 102a
A voltaic cell is constructed that uses the following half-cell reactions:
Cu+(aq) + e- → Cu(s)
I2(s) + 2 e- → 2 I-(aq)
The cell is operated at 298 K with [Cu+] = 0.25 M and [I-] = 0.035 M.
(a) Determine E for the cell at these concentrations.
Problem 102b,c
A voltaic cell is constructed that uses the following half-cell reactions:
Cu+(aq) + e- → Cu(s)
I2(s) + 2 e- → 2 I-(aq)
The cell is operated at 298 K with [Cu+] = 0.25 M and [I-] = 0.035 M.
(b) Which electrode is the anode of the cell?
(c) Is the answer to part (b) the same as it would be if the cell were operated under standard conditions?
- Using data from Appendix E, calculate the equilibrium constant for the disproportionation of the copper(I) ion at room temperature: 2 Cu+(aq) ⇌ Cu2+(aq) + Cu(s).
Problem 103