Why Electrolysis of ZnSO4 Won't Coat with Zinc Metal

In summary, the conversation discusses why electrolysis of aqueous zinc sulfate is not used for coating with zinc metal. The main reason is that H+ ions in the solution are preferentially discharged over Zn2+ ions, leading to the formation of sulfuric acid instead of zinc metal. This is due to the greater electrode potential of the reaction involving H+ ions. The conversation also touches upon the concept of cations facilitating the transfer of protons in the solution and the difference in molar equivalence of protons required for the two reactions. The exact answer provided states that the key factor is the comparison of reduction potentials between zinc and protons, and clarifies that this is an electrolytic pathway rather than a galvanic pathway.
  • #1
Hevonen
54
0
[SOLVED] Electrolysis, coating

2. Relevant equation
Why electrolysis of aqueous zinc sulfate is not used for coating with zinc metal?

The Attempt at a Solution


The following reaction has more positive electrode potential: (SO4)2- + 4H+ + 2e => H2SO3 + H2O than the reaction 2H+ + 2e- => H2(g); so H2SO3 would form at cathode. However, the right answer is that H+(aq) discharged preferentially because cations in solution =H+(aq),Zn2+(aq).
Do you know why?Thank you in advance!
 
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  • #2
Cations assist in transfer of the proton throughout the solution. It's similar to the notion that water conducts electricity better when it is more "ionic".
 
  • #3
GCT said:
Cations assist in transfer of the proton throughout the solution. It's similar to the notion that water conducts electricity better when it is more "ionic".

Do you mean that I cannot look straight away at the substance of greatest electrode potential?
 
  • #4
This question seems to be rather simple - when you have cations in solution it attracts the negatively charged sulfate

In addition this latter reaction requires 4 molar equivalence of protons compared to only 2 for the other reaction.

What are the respective values of the electrode potentials for both reactions and also please inform us on the exact answer for this problem. It seems to me that the conversion of the proton to hydrogen gas would be more favored as the formation of sulfuric acid from sulfate is not favored in many circumstances.
 
  • #5
Standard Electrode Potentials:

(SO4)2- + 4H+ + 2e => H2SO3 + H2O, E = +0.17V

2H+ + 2e- => H2(g), E = +0.00V

Exact answer:
Cations in the solution are H+(aq) and Zn2+(aq).
=> H+(aq) discharged preferentially (I do not understand this in the light of above potentials.)
 
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  • #6
What the answer is referring to is comparing the zinc reactions with that of the proton - in particular note the standard reduction potential of reducing zinc 2+ .

Remember , this isn't a galvanic pathway it is an electrolytic pathway.
 
  • #7
GCT said:
What the answer is referring to is comparing the zinc reactions with that of the proton - in particular note the standard reduction potential of reducing zinc 2+ .

Remember , this isn't a galvanic pathway it is an electrolytic pathway.

Thanks! Now, I understand. The key is the aqueous solution and electrolytic cell.
 

1. Why is the electrolysis of ZnSO4 not coating with zinc metal?

The electrolysis of ZnSO4 involves passing an electric current through a solution containing zinc sulfate and water. However, zinc metal will not be coated onto the surface because the reduction potential of zinc is lower than that of hydrogen. This means that hydrogen ions will be reduced at the cathode instead of zinc ions, preventing the zinc from coating onto the surface.

2. Can the electrolysis of ZnSO4 be made to coat with zinc metal?

Yes, the electrolysis of ZnSO4 can be made to coat with zinc metal by using a different cathode material with a lower reduction potential, such as copper. This will allow the zinc ions to be reduced onto the surface of the cathode instead of hydrogen ions.

3. Are there any other factors that can affect the electrolysis of ZnSO4 coating with zinc metal?

Yes, the concentration of ZnSO4 in the solution can also affect the electrolysis process. Higher concentrations of ZnSO4 will result in a higher concentration of zinc ions in the solution, increasing the chances of zinc coating onto the surface of the cathode.

4. How does the temperature of the solution affect the electrolysis of ZnSO4 coating with zinc metal?

The temperature of the solution can also affect the electrolysis process. Higher temperatures can increase the rate of the reaction, allowing for more zinc ions to be reduced onto the cathode surface. However, too high of a temperature can also lead to the evaporation of the solution and result in a less effective coating of zinc.

5. Can impurities in the solution affect the electrolysis of ZnSO4 coating with zinc metal?

Yes, impurities in the solution can affect the electrolysis process and prevent zinc from coating onto the surface. For example, if there are other metal ions present in the solution, they may have a higher reduction potential than zinc and be reduced onto the cathode instead. This can be prevented by ensuring the solution is pure and free of any other metal ions.

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