Review the following concepts if necessary:
 Redox Reactions for AP Chemistry
 Electrochemical Cells for AP Chemistry
 Quantitative Aspects of Electrochemistry for AP Chemistry
 Nernst Equation for AP Chemistry
Questions
First FreeResponse Question
Answer the following question in 15 minutes. You may not use a calculator. You may use the tables at the back of the book.
The above galvanic cell is constructed with a cobalt electrode in a 1.0 M Co(NO_{3})_{2} solution in the left compartment, and a silver electrode in a 1.0 M AgNO_{3} solution in the right compartment. The salt bridge contains a KNO_{3} solution. The cell voltage is positive.
 What is the balanced net ionic equation for the reaction, and what is the cell potential?
 Which electrode is the anode? Justify your answer.
 Could KCl be substituted for the KNO_{3} in the salt bridge? Justify your answer.
 If some solid Co(NO_{3})_{2} is added to the cobalt compartment, what will happen to the voltage? Justify your answer.
 If the cell is allowed to operate until equilibrium is established, what will the potential be? Justify your answer.
Second FreeResponse Question
You have 15 minutes to answer the following questions. You may not use a calculator. You may use the tables in the back of the book.
The above galvanic cell is constructed with a cadmium electrode in a 1.0 M Cd(NO_{3})_{2} solution in the left compartment, and a silver electrode in a 1.0 M AgNO_{3} solution in the right compartment. The salt bridge contains a KNO_{3} solution. The cell voltage is positive.
 What is the balanced net ionic equation for the reaction, and what is the cell potential?
 Show how to calculate the equilibrium constant for the cell.
 Write the expression for Q that would be needed in the Nernst equation. Explain why any substances from the net ionic equation do not appear in Q.
 Show how to calculate the free energy for the reaction.
 Identify the anode, the cathode, the oxidizing agent, and the reducing agent.
Answers And Explanations
First FreeResponse Question
 The cell reaction is:
 The cobalt is the anode. You get 1 point for this statement.
 KCl cannot be substituted for KNO_{3} in this case. This is worth 1 point.
 The voltage would decrease. Give yourself 1 point for this answer.
 At equilibrium the cell voltage would be 0 V. This is worth 1 point. At equilibrium no work is done, so the potential must be zero. Give yourself 1 point for this answer.
Give yourself 1 point if you got this correct. The physical states are not necessary.
The calculation of the cell potential may be done in different ways. Here is one method:
Give yourself 1 point for the correct answer regardless of the method used. The most common mistake is to multiply the silver voltage by two. You do not get the point for an answer of 1 V.
The halfreactions and their standard reductions potentials are supplied on the exam, not in the problem as given here. You will be expected to find the appropriate halfreactions in a table.
The reason Co is the anode is because the Co is oxidized. You get 1 point for this statement, or if you say the Co loses electrons.
The Cl^{–} ion from the KCl would react with the silver ion to give insoluble AgCl. Give yourself 1 point for this explanation.
The excess Co^{2+}, from the Co(NO_{3})_{2}, would make the cell nonstandard. The Nernst equation should be used to calculate the new voltage. The concentration of the cobalt ions appears in the numerator of the logarithm term of the Nernst equation. This makes the logarithm term more negative, yielding a lower voltage. Give yourself 1 point for any answer relating to this. It might be helpful if you wrote out the Nernst equation for this cell.
There are a total of 10 points possible on these questions.

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