Chapter 17 Notes Electro

AP Chemistry: Chapter 17 Student Notes

Objectives

17.1a: Review Redox

Assign Oxidation Numbers to the following:
a. HNO3
b. PbSO4
c. (NH4)2Ce(SO4)3

Balance the following in acidic medium
Al (s) + MnO4- (aq)  Al3+ (aq) + Mn2+ (aq)

Balance the following in a basic medium
Mg (s) + OCl- (aq)  Mg(OH)2 (s) + Cl- (aq)

Balance the following Redox Reaction: The big nasty problem

K4Fe(CN)6 + KMnO4 + H2SO4  KHSO4 + Fe2(SO4)3 + MnSO4 + HNO3 + CO2 +H2O

17.1: Galvanic Cells

Review of Redox Reactions

Oxidation: _______________________

Reduction: ___________________________

How to make a __________________ _____________________ (gc) Which is a _____________________

You need to make separate __________________ for each _____________ reaction.

The problem with this cell is …..
If you put a ______________ ________________ the cell will produce ___________ for a long time.

Galvanic Cells: Label All parts

What happens when one of the electrodes is not a metal?

17.2: Standard Reduction Potentials

Calculating & Using Electrical Potential

The table above assumes that you have a __________ M solution at ________atm and _________ºC

Example 1: What would be the electrical potential for the reaction:
PbO2 + Na  Pb2+ + Na+

Fe3+ + Mg  Mg2+ + Fe2+

Example 2:
Is H2(g) capable of reducing Ag+(aq)

Is H2(g) capable of reducing Ni2+ (aq)

Is Fe2+ (aq) capable of reducing VO2+

Is Fe2+ capable fo reducing Cr3+ (aq)

Example 3: Rank the following from strongest oxidizing agent to weakest oxidizing agent:
Ce4+ Ce3+ Fe2+ Fe3+
Mg2+ Mg Ni2+ Sn
17.3: Cell Potential and Equilibrium
∆G=-nFEº

Example: Using the data in table 17.1, calculate ∆Gº for the reaction:
Cu2+ (aq) + Fe(s)  Cu(s) + Fe2+ (aq)

17.4: The Nernst Equation
What happens when concentration and temperatures are not standard?
Nernst Equation

Sometimes written as: Assuming 25ºC

Example 1: What is the electrical potential for the following cell with the following concentrations?
VO2+ + Zn  Zn2+ + VO2+
[VO2+] = 2.0 M [H+] = 0.50 M
[VO2+] = 1.0 x 10-2 M [Zn2+] = 0.10 M

First: Write the balanced equation: Use the table of reduction potentials

Second: find Eº

Third: Use the Nernst Equation and plug in the concentration values for Q
Concentration Cells:

17.4-17.5: Batteries and Corrosion

A Galvanic Cell or a series of galvanic cells hooked together.

Corrosion

17.7: Electrolysis
The opposite of a galvanic cell: Pump electricity through a non ___________ reaction.

Comparison of a galvanic cell and an electrolytic cell

Electrolytic Cell ____________________________

Electrolysis __________________________________

Ampere: ___________________________

Faraday ________________________________

The Story of Aluminum

Example 1: Calculate the amount of time required to produce 1000 g of magnesium metal by electrolysis of molten MgCl2 using a current of 50A.

Example 2:
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?

What amperage is required to plate out 0.250 mol Cr form a Cr3+ solution in a period of 8.00 hours?

Example 3:
What reaction will take place at the cathode and the anode when each of the following is electrolyzed?
a. 1.0 M KF solution

b. 1.0 M CuCl2 solution

c. 1.0 M H2O2 solution containing 1.0 M HCl

10, 122, 299 ---> 162, 5, 122, 60, 60, 188
AP Style Questions
2002

The Diagram below shows the experimental setup for a typical electrochemical cell that contains two standard half-cells. The cell operates according to the reaction represented by the following equation:
Zn(s) + Ni2+ (aq)  Ni(s) + Zn2+ (aq)

a) Identify the M and M2+ in the diagram and specify the initial concentration for M2+ in solution.
b) Indicate which of the metal electrodes is the cathode. Write the balanced equation for the reaction that occurs in the half-cell containing the cathode.
c) What would be the effect on the cell voltage if the concentration of Zn2+ was reduced to 0.100M in the half cell containing the Zn electrode.
d) Describe what would happen to the cell voltage if the salt bridge was removed. Explain.
2000
Answer the following questions that relate to electrochemical reactions.
1) Under standard conditions at ° C , Zn(s) reacts with Co2+aq) to produce CO(s).
a) Write the balanced equation for the oxidation reaction.
b) Write the balanced net ionic equation for the overall reaction.
c) Calculate the standard potential, °, for the overall reaction at ° C .
2) At ° C , H2O2 decomposes according to the following equation.
2H2O2 (aq)  2H2O(l) + O2(g) E° = 0.55 V
a) Determine the value of the standard free energy, G°, for the reaction at ° C.
b) Determine the value of the equilibrium constant Keq , for the reaction at ° C.
c) The standard reduction potential E°, for the half reaction O2(g) +4H+ +4e-  2H2O(l) has a value of 1.23V. Using the information in addition to the information given above, determine the value of the standard reduction potential, E° , for the reaction below.
O2(g) + 2H+(a) +2e-  H2O2(aq)
d) In an electrolytic cell, Cu(s) is produced by the electrolysis of CusSO4(aq). Calculate the maximum mass of Cu(s) that can be deposited by a direct current of 100. amperes passed through 5.00L of 2.00M CuSO4(aq) for a period of 1.00 hours.