Electrochemistry Chapter 11 Email benzene 4 presidentgmail com

Electrochemistry Chapter 11 E-mail: benzene 4 president@gmail. com Web-site: http: //clas. sa. ucsb. edu/staff/terri/

Electrochemistry – ch 11 1. Consider the following reaction: a. What substance is getting reduced? b. How many moles of electrons are transferred? 2 VO 2+ + 4 H+ + Cd → 2 VO 2+ + 2 H 2 O + Cd 2+

Electrochemistry – ch 11 2. Which is the strongest oxidizing agent? a. Mn 2+ b. Br – Half-Reaction c. Br 2 + 2 e – → 2 Br – d. Ag+ e. Li E°red (V) 1. 09 Ag+ + e – → Ag 0. 80 Mn 2+ + 2 e – → Mn – 1. 18 Li+ + e – → Li – 3. 05

Electrochemistry – ch 11 3. Which is the strongest reducing agent? a. Na+ b. Al Half-Reaction 2+ c. Zn F 2 + 2 e – → 2 F – d. FZn 2+ + 2 e – → Zn e. Mn 2+ – Mn + 2 e → Mn E°red (V) 2. 87 – 0. 76 – 1. 18 Al 3+ + 3 e – → Al – 1. 66 Na+ + e – → Na – 2. 71

Electrochemistry – ch 11 4. True or false: a. Galvanic cells spontaneously produce a current under standard conditions b. Electrons flow from the anode to cathode in a voltaic cell c. Oxidation occurs at the cathode d. Corrosion of a metal occurs at the anode

Electrochemistry – ch 11 5. You designed a galvanic cell with silver and gold electrodes. Assign the electrodes, write the overall reaction, and calculate the standard cell potential. As the cell operates what happens to the masses of the silver and gold electrodes? Half-Reaction Ag 1. 0 M Ag+ Au 1. 0 M Au 3+ E°red (V) Au 3+ + 3 e – → Au 1. 50 Ag+ + e – → Ag 0. 80

Electrochemistry – ch 11 6. Using reduction potentials answer the following: a. Is Cl 2 able to reduce Cr 3+? b. Is Pb 2+ able to oxidize Ni? c. Will Au dissolve in an acidic solution? d. Will Zn dissolve in an acidic solution? e. What can oxidize Al but not Zn? f. What can reduce Zn 2+ but not Na+? Half-Reaction E°red (V) F 2 + 2 e – → 2 F – 2. 87 Au 3+ + 3 e – → Au 1. 50 Cl 2 + 2 e– → 2 Cl– 1. 36 2 H+ + 2 e – → H 2 0. 00 Pb 2+ + 2 e– → Pb – 0. 13 Ni 2+ + 2 e– → Ni – 0. 23 Cr 3+ +3 e– → Cr – 0. 73 Zn 2+ + 2 e – → Zn – 0. 76 Mn 2+ + 2 e – → Mn – 1. 18 Al 3+ + 3 e – → Al – 1. 66 Na+ + e – → Na – 2. 71

Electrochemistry – ch 11 7. Consider the following reaction for a voltaic cell at 75 °C. Pb 2+(aq) + 2 Cr 2+(aq) → Pb(s) + 2 Cr 3+(aq) a. Calculate the initial cell voltage for the above reaction if the initial concentrations are [Pb 2+] = 0. 25 M, [Cr 2+] = 0. 20 M and [Cr 3+] = 0. 005 M. b. Will the initial potential increase, decrease or remain the same if the volume of electrodes is doubled by adding water? c. Will the initial potential increase, decrease or remain the same if the solid lead is cut in half? d. Will the initial potential increase, decrease or remain the same if you add Na. Cl causing Pb. Cl 2 to precipitate out of solution? Half-Reaction E°red (V) Pb 2+ + 2 e– → Pb – 0. 13 Cr 3+ + e– → Cr 2+ – 0. 50

Electrochemistry – ch 11 8. Consider the following cell: Cu (s) | Cu 2+(aq)(0. 001 M) || Fe 3+(aq)(0. 02 M) , Fe 2+(aq) (? M) | Pt(s) Determine the concentration of the Fe 2+ if the measured cell voltage at 27°C is 0. 5 V. Half-Reaction E°red (V) Fe 3+ + e– → Fe 2+ 0. 77 Cu 2+ + 2 e– → Cu 0. 34

Electrochemistry – ch 11 9. Consider the following cell: Al(s) | Al 3+ (1. 0 M) | | Pb 2+(1. 0 M) | Pb (s) Calculate the cell potential after the reaction has operated long enough for the [Al 3+] to have changed by 0. 66 M at 25 °C. Half-Reaction E°red (V) Pb 2+ + 2 e– → Pb – 0. 13 Al 3+ + 3 e – → Al – 1. 66

Electrochemistry – ch 11 10. Consider the Galvanic cell at 25 °C described as follows: X | X 2+ || Y 3+ | Y Where X and Y are unknown metals. Given the standard reduction potential for Y 3+ is 1. 5 V and that K for the overall reaction in this Galvanic cell is 1. 2 x 1020 what is the standard reduction potential of X 2+?

Electrochemistry – ch 11 11. Consider two electrodes connected by a wire. One side has 0. 0001 M Fe 2+/Fe (s) and the other side has 10 M Fe 2+/Fe(s). a. Assign the electrodes b. Calculate the cell voltage at 25 °C. Fe 2+ + 2 e– → Fe E°red = – 0. 44 V

Electrochemistry – ch 11 12. What mass of Co (58. 93 g/mol) will plate out from a solution of Co 2+ when a current of 15 amps is applied for 1. 15 hours?

Electrochemistry – ch 11 13. How long will it take (in min) to plate out 10. 0 g of Bi (209 g/mol) from a solution of Bi. O+ using a current of 25. 0 A?

Electrochemistry – ch 11 14. It takes 24 min to plate out 9. 8 g of an unknown metal (M) from a solution of MCl 3 when a current of 10 amps is applied. Identify the metal.

Electrochemistry – ch 11 15. What volume of gas at STP is produced from the electrolysis of water by a current of 3. 5 amps in 15 minutes? 2 H 2 O (l) → 2 H 2(g) + O 2(g)

Electrochemistry – ch 11 You have completed ch 11

Electrochemistry – ch 11 – Answers 1. Consider the following reaction: a. What substance is getting reduced? VO 2+ b. How many moles of electrons are transferred? 2 2 VO 2+ + 4 H+ + Cd → 2 VO 2+ + 2 H 2 O + Cd 2+ +5 +4 Oxidation number for V is decreasing ⇒ Getting reduced

Electrochemistry – ch 11 – Answers 2. Which is the strongest oxidizing agent? a. Mn 2+ b. Br√ c. Br 2 d. Ag+ 3. Which is the strongest reducing agent? a. Na+ √ b. Al c. Zn 2+ d. Fe. Mn

Electrochemistry – ch 11 – Answers 4. Which of the following are true about galvanic cells (aka. voltaic cells): √ a. Spontaneously produce a current b. A current must be provided in order to run c. Oxidation occurs at the cathode √ d. Have possible plating out of metals at the cathode √ e. The current flows from anode to cathode f. The concentrations at the electrodes are 1 M

Electrochemistry – ch 11 – Answers 5. You want to design a galvanic cell with silver and gold electrodes. Show or describe how you would set it up? Assign the electrodes, write the overall reaction, and calculate the standard cell potential. As the cell operates what happens to the masses of the silver and gold electrodes? Cathode ½: Au 3+ + 3 e– → Au Anode ½: Ag → Ag+ + e– E° = 1. 5 V E° = 0. 8 V Overall Rxn: Au 3+(aq) + 3 Ag(s) → Au(s) + 3 Ag+(aq) Ecell° = 0. 7 V The cathode is getting plated with Au so the mass is getting heavier and at the anode Ag is corroding so the mass is going down.

Electrochemistry – ch 11 – Answers 6. Using reduction potentials answer the following: a. Is Cl 2 able to reduce Cr 3+? No Cl 2 is an oxidizing reagent b. Is Pb 2+ able to oxidize Ni? Yes c. Will Au dissolve in an HCl solution? No d. Will Zn dissolve in an HCl solution? Yes e. What can oxidize Al but not Zn? Mn 2+ f. What can reduce Zn 2+ but not Na+? Mn or Al