Electrochemistry ❮ 257❯ Free-Response Question
You have 15 minutes to answer the following long question. You may use a calculator and
the tables in the back of the book.QuestionThe above galvanic cell is constructed with a cobalt electrode in a 1.0 M Co(NO 3 ) 2 solu-
tion 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.
(a) What is the balanced net ionic equation for the reaction, and what is the cell potential?
Co^2 + + 2e– → Co E° = +0.28 V
Ag+ + 1e- → Ag E° = +0.80 V
(b) Which electrode is the anode? Justify your answer.
(c) If some solid Co(NO 3 ) 2 is added to the cobalt compartment, what will happen to the
voltage? Justify your answer.
(d) If the cell operates until equilibrium is established, what will the potential be? Justify
your answer.
(e) Write the electron configurations for Co and Co^2 +.❯ Answer and Explanation
(a) The cell reaction is
Co(s) + 2 Ag+(aq) → Co^2 +(aq) + 2 Ag(s)The calculation of the cell potential may be done in different ways. Here is one method:
Co → Co^2 + + 2 e- E° = +0.28 V
2(Ag+ + 1 e- → Ag) E° = +0.80 V
Co(s) + 2 Ag+ (aq) → Co^2 + (aq) + 2 Ag(s) E° = +1.08 V
Give yourself 1 point if you got the correct equation. The physical states are not
necessary. Give yourself 1 point for the correct answer (1.08 V) regardless of the
method used. The most common mistake is to multiply the silver voltage by 2. You do
not get the point for an answer of 1 V.