Electrochemical cell question - strip on Zn in contact with zn2+/CN solution

In summary, the potential at which a Zn electrode in contact with a solution containing 0.01 mol Zn2+ and 3.0 mol CN- per litre can be calculated using the Nernst equation and the equilibrium constant β. The reaction quotient Q can be found using a RICE table and the free ion concentration. This potential can be significantly affected by the addition of complexing agents and adjusting the pH of the solution.
  • #1
saucer5
1
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The potential at which a metal is deposited in the electrowinning process can significantly affect the quality of the deposit. The potential itself can be dramatically affected by the addition of complexing agents and by adjusting the pH of the solution as the following calculations demonstrate. (assume 298 K)

a) Calculate the potential of an electrode consisting of a strip of Zn in contact with a solution containing 0.01 mol Zn2+ and 3.0 mol CN‐ per litre. The ε° value for aquated Zn2+ is ‐0.76 V, and β = 1 x 10^9 for the Zn2+ / CN‐ equilibrium.


b) ε = ε° ‐ (RT/nF) ln Q
where Q is the reaction quotient. Also useful is that β= [Zn(CN)]/[CN]^2[Zn]

n is the number of electrons transferred to transform Zn ion to Zn solid (2)


c) I tried to do a RICE table using β = 10^9 = x / (0.01-x) (3-2x)^2. assuming that on the bottom, the x values are negligible. However, this isn't correct.

I am given that ε = -0.76, RT/nF = 0.0128. The main problem in this computation is that I have no idea what the reaction quotient should be. I know it is usually based on the half cell equation, which would be ln (1/Zn2+), which I thought I could figure out using the RICE table...but given that the x is negligible...arhghweoufwe!

Help!
 
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  • #2
Your approach looks OK to me. However, you should calculate not concentration of a complex, but concentration of a free ion - and put this free ion concentration the into Nernst equation.
 

1. What is an electrochemical cell?

An electrochemical cell is a device that converts chemical energy into electrical energy. It consists of two electrodes, a positive (anode) and a negative (cathode), that are connected by an electrolyte solution. The flow of electrons between the electrodes creates an electrical current.

2. How does an electrochemical cell work?

In an electrochemical cell, one electrode undergoes an oxidation reaction, releasing electrons into the external circuit. These electrons flow through the external circuit to the other electrode, where a reduction reaction takes place, consuming the electrons. The electrolyte solution allows for the transfer of ions between the electrodes, completing the circuit.

3. What is the purpose of the strip of Zn in contact with the Zn2+/CN solution?

The strip of Zn acts as the anode in the electrochemical cell. It undergoes oxidation, releasing electrons into the external circuit. The Zn2+/CN solution acts as the electrolyte, allowing for the transfer of Zn2+ ions to the cathode.

4. What is the role of the Zn2+ ions in this electrochemical cell?

The Zn2+ ions serve as the charge carriers in the electrolyte solution. They travel from the anode to the cathode, completing the circuit and allowing for the flow of electrons. Without these ions, the electrochemical cell would not be able to produce an electrical current.

5. How does the contact between the strip of Zn and the Zn2+/CN solution affect the electrochemical cell?

The contact between the strip of Zn and the Zn2+/CN solution is crucial for the electrochemical cell to function. It allows for the transfer of electrons and ions between the anode and cathode, completing the circuit and generating an electrical current. Without this contact, the electrochemical cell would not work.

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