Ch.20 - Electrochemistry

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Tro 6th Edition

Ch.20 - Electrochemistry

Problem 102

How can one sketch an electrolysis cell that electroplates nickel onto other metal surfaces, labeling the anode and cathode and indicating the reactions that occur at each?

Problem 104

Silver can be electroplated at the cathode of an electrolysis cell by the half-reaction: Ag⁺(aq) + e^– → Ag(s) What mass of silver would plate onto the cathode if a current of 6.8 A flowed through the cell for 72 min?

Problem 105

A major source of sodium metal is the electrolysis of molten sodium chloride. What magnitude of current produces 1.0 kg of sodium metal in 1 hour?

Problem 107

Consider the reaction shown here occurring at 25 °C: A(s) + B2+(aq) → A2+(aq) + B(s). Given that ∆Gr°xn = -14.0 kJ, determine the value of Ec°ell and K for the reaction, and complete the following table for [B2+], [A2+], Q, Ecell, and ∆Grxn with initial values 1.00, 1, 1.0 * 10^-4, 3.54 * 10^-3, and 1.00 * 10^-4 respectively.

Problem 108

Consider the reaction shown here occurring at 25°C. Cr(s) + Cd²⁺(aq) → Cr²⁺(aq) + Cd(s) Determine E°_cell, K, and ∆G°_rxn for the reaction and complete the table.

[Cd²⁺] [Cr²⁺] Q E_cell 𝚫G_rxn

1.00 1.00

1.00 1.00 × 10^-5

1.00 × 10^-5 1.00

4.18 × 10^-4 1.00

Problem 109

Consider the unbalanced redox reaction: MnO4-(aq) + Zn(s) → Mn2+(aq) + Zn2+(aq). Balance the equation and determine the volume of a 0.500 M KMnO4 solution required to completely react with 2.85 g of Zn.

Problem 110

Consider the unbalanced redox reaction: Cr₂O₇^2-(aq) + Cu(s) → Cr³⁺(aq) + Cu²⁺(aq) Balance the equation and determine the volume of a 0.850 M K₂Cr₂O₇ solution required to completely react with 5.25 g of Cu.

Problem 113a

Determine whether HI can dissolve each metal sample. If it can, write a balanced chemical reaction showing how the metal dissolves in HI and determine the minimum volume of 3.5 M HI required to completely dissolve the sample. a. 2.15 g Al

Problem 113b

Problem 114

Determine if HNO₃ can dissolve each metal sample. If it can, write a balanced chemical reaction showing how the metal dissolves in HNO3 and determine the minimum volume of 6.0 M HNO3 required to completely dissolve the sample. a. 5.90 g Au b. 2.55 g Cu c. 4.83 g Sn

Problem 116

The cell potential of this electrochemical cell depends on the gold concentration in the cathode half-cell. Pt(s) | H₂(g, 1.0 atm) | H⁺(aq, 1.0 M) || Au³⁺(aq, ? M) | Au(s) What is the concentration of Au³⁺ in the solution if E_cell is 1.22 V?

Problem 117

A friend wants you to invest in a new battery she has designed that produces 24 V in a single voltaic cell. Why should you be wary of investing in such a battery?

Problem 119a

A battery relies on the oxidation of magnesium and the reduction of Cu²⁺. The initial concentrations of Mg²⁺ and Cu²⁺ are 1.0 × 10^–4 M and 1.5 M, respectively, in 1.0-liter half-cells. a. What is the initial voltage of the battery?

Problem 119b

Problem 119c

Problem 120a

A rechargeable battery is constructed based on a concentration cell constructed of two Ag/Ag⁺ half-cells. The volume of each half-cell is 2.0 L, and the concentrations of Ag⁺ in the half-cells are 1.25 M and 1.0×10^–3 M. a. How long can this battery deliver 2.5 Aof current before it goes dead?

Problem 120b

A rechargeable battery is constructed based on a concentration cell constructed of two Ag/Ag⁺ half-cells. The volume of each half-cell is 2.0 L, and the concentrations of Ag⁺ in the half-cells are 1.25 M and 1.0 × 10^–3 M. b. What mass of silver is plated onto the cathode by running at 3.5 A for 5.5 h?

Problem 120c

A rechargeable battery is constructed based on a concentration cell constructed of two Ag/Ag⁺ half-cells. The volume of each half-cell is 2.0 L, and the concentrations of Ag⁺ in the half-cells are 1.25 M and 1.0 × 10^–3 M. c. Upon recharging, how long would it take to redissolve 1.00 × 10² g of silver at a charging current of 10.0 amps?

Problem 121

If a water electrolysis cell operates at a current of 7.8 A, how long will it take to generate 25.0 L of hydrogen gas at a pressure of 25.0 atm and a temperature of 25 °C?

Problem 123

The Ksp of CuI is 1.1 * 10^-12. Find Ecell for the cell: Cu(s) | CuI(s) | I^-(aq)(1.0 M) || Cu^+(aq)(1.0 M) | Cu(s)

Problem 126a

Calculate ∆G°_rxn and K for each reaction. a. The reaction of Cr²⁺(aq) with Cr₂O₇^2–(aq) in acid solution to form Cr³⁺(aq).

Problem 126b

Calculate ∆G°_rxn and K for each reaction. b. The reaction of Cr³⁺(aq) and Cr(s) to form Cr²⁺(aq). [The electrode potential of Cr²⁺(aq) to Cr(s) is -0.91 V.]

Problem 127

The molar mass of a metal (M) is 50.9 g/mol; it forms a chloride of unknown composition. Electrolysis of a sample of the molten chloride with a current of 6.42 A for 23.6 minutes produces 1.20 g of M at the cathode. Determine the empirical formula of the chloride.

Problem 128

A metal forms the fluoride MF₃. Electrolysis of the molten fluo- ride by a current of 3.86 A for 16.2 minutes deposits 1.25 g of the metal. Calculate the molar mass of the metal.

Problem 129

A sample of impure tin of mass 0.535 g is dissolved in strong acid to give a solution of Sn²⁺. The solution is then titrated with a 0.0448 M solution of NO₃^–, which is reduced to NO(g). The equivalence point is reached upon the addition of 0.0344 L of the NO₃^– solution. Find the percent by mass of tin in the original sample, assuming that it contains no other reducing agents.

Problem 131

A current of 11.3 A is applied to 1.25 L of a solution of 0.552 M HBr converting some of the H⁺ to H₂(g), which bubles out of solution. What is the pH of the solution after 73 minutes?

Problem 134

To what pH should you adjust a standard hydrogen electrode to get an electrode potential of -0.122 V? (Assume that the partial pressure of hydrogen gas remains at 1 atm.)