Problem: A voltaic cell is constructed that uses the following half-cell reactions:l Cu+ (aq) + e-  →  Cu(s)I2 (s) + 2e-  →  2I- (aq).The cell is operated at 298 K with [Cu+ ] = 0.26 M and [I- ] = 3.6 M .If [Cu+ ] was equal to 0.16 M , at what concentration of I- would the cell have zero potential?

FREE Expert Solution

We’re asked to determine the concentration of I- if the cell potential, Ecell is zero and [Cu+] = 0.16 M


We will use the Nernst Equation which relates the concentrations of compounds and cell potential:

 

Ecell=E°cell-0.592 Vnlog Q

Ecell = cell potential under non-standard conditions
cell = standard cell potential
n = number of e- transferred
Q= reaction quotient = [products]/[reactants] 


In the Nernst Equation, the E°cell is needed but only Ecell was given. We have to determine the E°cell first and as well as the anode (oxidation)and cathode (reduction) in the concentration cell and the number of electrons transferred (n).


We will find Q to solve for [I-] by doing these steps:


Step 1. Write the two half-cell reactions and determine the half-cell potentials (refer to the Standard Reduction Potential Table)
Step 2. Identify the reduction half-reaction (cathode) and the oxidation half-reaction (anode)
Step 3. Get the overall reaction by balancing the number of electrons transferred then adding the reduction half-reaction and oxidation half-reaction.
Step 4. Calculate E°cell.

Step 5. Calculate [I-] when Ecell = 0 using the Nernst Equation.

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Problem Details
A voltaic cell is constructed that uses the following half-cell reactions:
l Cu+ (aq) + e-  →  Cu(s)
I2 (s) + 2e-  →  2I- (aq)


.
The cell is operated at 298 K with [Cu+ ] = 0.26 M and [I- ] = 3.6 M .

If [Cu+ ] was equal to 0.16 M , at what concentration of I- would the cell have zero potential?

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