Electrochemical_Cells

PRELAB Electrochemical Cells NAME DATE SECTION PRELAB • 147 Standard Reduction Potential Half-Reaction E°, Volts Ca 2 + (aq) + 2 e – → Ca (s) – 2.87 Mn 2 + (aq) + 2 e – → Mn (s) – 1.18 Co 2 + (aq) + 2 e – → Co (s) – 0.28 2 H + (aq) + 2 e – → H 2 (g) – 0.00 Ag + (aq) + e – → Ag (s) + 0.80 Cl 2 (g) + 2 e – → 2Cl – (aq) + 1.36 Given the partial list of standard reduction potentials above, answer Questions 1–5. 1. Will calcium (Ca) spontaneously reduce silver ion (Ag + ) to silver (Ag)? Briefly explain your answer. If yes, what is E°?

148 • PRELAB CHEMISTRY 1225L 2. Will silver metal react spontaneously with HCl (aq) to produce H 2 (g)? Briefly explain. 3. What is the cell potential for the Mn/Mn 2 + ||Co 2 + /Co cell, based on the standard poten- tials given above? 4. Will the reaction between Ca 2 + and Cl – ions to form Ca metal and Cl 2 (g) be spontaneous? Briefly explain. 5. A student constructed a Mg/Mg 2 + ||Ag + /Ag cell and measured a cell potential of 3.17 volts. Calculate the reduction potential of the Mg/Mg 2 + half-reaction.

REPORT SHEET • 151 REPORT SHEET ElectrocSemical Cells NAME DATE SECTION Part II: Electrolytic Cells Mass of KI, g _______________________ initial pH _______________________ electrolysis – finish time _______________________ electrolysis – start time _______________________ time of electrolysis, min _______________________ final pH _______________________ Observations after several minutes of electrolysis: Observations at the end of the electrolysis:

152 • REPORT SHEET CHEMISTRY 1225L Calculations Part I: Voltaic Cells A. Cell Potentials Using a Zn(s)/Zn 2 + (aq) Reference Electrode Complete the following table using your mean values for Part I A, and assigning a reference voltage of 0.00 volts for the reduction of Zn 2 + to Zn. Put the voltages in increasing order. Half-Reaction Standard Reduction Potential at 25 °C, Volts Zn 2 + (aq) + 2 e – → Zn (s) ____0.00____ → ____________ → ____________ → ____________ B. Cell Potentials Using the Table Above Redox Couple predicted voltage observed voltage percent error* 1. Pb/Cu ______________ _____________ ___________ 2. Fe/Cu ______________ _____________ ___________ 3. Fe/Pb ______________ _____________ ___________ *Percent error is calculated by the formula: % . . . error pred voltage pred voltage obs voltage 100 # = -

154 • REPORT SHEET CHEMISTRY 1225L 2. The cell voltage, E°, is __________ volts. 3. a. The oxidizing agent is ____________________. b. The reducing agent is ____________________. 4. Moles of KI used: _____________________ 5. a. Initial OH – concentration, mol/L ______________________ b. Initial moles of OH – ______________________ c. Final OH – concentration, mol/L ______________________ d. Final moles of OH – ______________________ e. Moles of OH – produced (d – b) ______________________

POSTLAB Electrochemical Cells NAME DATE SECTION POSTLAB • 155 1. For the following voltaic cells studied in this experiment, (1) write the oxidation and reduction half-equations, (2) identify the oxidizing and reducing agents, and (3) write the overall cell reaction. a. Zn/Fe b. Pb/Cu 2. If the cells you constructed in this experiment were doubled in size, would the measured potentials double? Briefly explain.