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Electrochemical Cell Potential Under Non-Standard Conditions

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Consider the electrochemical cell:
Pt|Cr2+(0.2752 M), Cr3+(1.705 M)||Co2+(0.2008 M)|Co
a. What is the cell potential (hint: you can solve the problem by half-reactions or by the over-all reaction, both will give you the same answer so you can double check yourself)?
b. Is the cell galvanic or electrolytic (must show math in part (a) to get credit for answer)?

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Solution Preview

Please see attached World file as there are equations involved in the calculations that does not show up here.

A. I will do this the over-all reaction way as I feel it is easier:

From the cell notation the anode is Always written on the left side of the double line and the cathode is on the right side.

So Anode is Cr2+/Cr3+ couple. This is where oxidation occurs. Write an oxidation half-reaction where the electrons are on the product side (because oxidation means loss of ...

Solution Summary

This solution contains step-by-step instructions on how to obtain reduction and oxidation half-reactions from the cell notation, how to obtain the cell potential under standard conditions using tabulated tables, and how to correct the cell potential for non-standard conditions using the Nernst equation. Detailed calculations are contained in the attached Word file.

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Half Cell Reaction, standard Potential, Free Energy

The reaction between silver ion and solid zinc is represented by the following equation.

2 Ag+ (aq) + Zn(s) ---> Zn2+(aq) + 2Ag(s)

(a) A 1.50 sample of Zn is combined with 250 ml of 0.110 M AgNO3 at 25oC.
(i) Identify the limiting reactant. Show calculations to support your answer.
(ii) On the basis of limiting reactants that you identified in part (i), determine the value of the [Zn2+] after the reaction is complete. Assume that volume change is negligible.

(b) Determine the value of the standard potential, Eo, for a galvanic cell based on the reaction between AgNO3(aq) and solid Zn at 25 C.

Another galvanic cell is based on the reaction between Ag+(aq) and Cu(s), represented by the equation below. At 25 C, the standard potential, Eo, for the cell is 0.46 V.

2 Ag+ (aq) + Cu(s) ---> Cu2+(aq) + 2Ag(s)

(c) Determine the value of the standard free-energy change, deltaGo, for the reaction between Ag+ (aq) and Cu(s) at 25 C.

(d) The cell is constructed so that [Cu2+] is 0.045 M and [Ag+] is 0.010 M. Calculate the value of the potential E for the cell.

(e) Under the conditions specified in part (d), is the reaction in the cell spontaneous? Justify your answer.

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