Electrochemical cells

[predentlove]

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Electrode potentials are :
Zn --> Zn2+ + 2e E=+0.76V
Au --> Au3+ + 3e E=-1.42V
If a gold foil were placed in a solution containing zinc ions, what would be the reaction potential.

The answer is -2.18V... But I got +2.18V

How would we know what is reduced/oxidized in this case?
I said that the Zn was oxidized and Au was reduced because the Ecell would be positive in that fashion.

Am I wrong? :/

 

[mh0000]

Electrode potentials are :
Zn --> Zn2+ + 2e E=+0.76V
Au --> Au3+ + 3e E=-1.42V
If a gold foil were placed in a solution containing zinc ions, what would be the reaction potential.

The answer is -2.18V... But I got +2.18V

How would we know what is reduced/oxidized in this case?
I said that the Zn was oxidized and Au was reduced because the Ecell would be positive in that fashion.

Am I wrong? :/

EDIT: Changed explanation, wasn't paying attention. The gold film is in the elemental form, and will not be reduced. The zinc ion is already ionized and will not be oxidized. So if there is to be a reaction, gold will have to be oxidized and zinc reduced. To calculate the E of such reaction, keep the gold E written as it is (since it's being oxidized) and add the negative of the zinc E (because we're reversing it since it will be reduced). There will be no spontaneous reaction since the reaction E is negative and an electrolytic cell would need to be construct an to carry out the reaction of plating zinc.

-1.42 + (-0.76) = -2.18V

 

[LetsGo2DSchool]

You can figure it out just by the wording. It says gold foil so it has to be Au in its elemental form thus it will be: Au ---> to something. It says zinc ions and thus it will be: Zn2+ ---> to something.

Then by looking at the given equations you know the combo needs to be:

Au --->Au3+ + 3e E =-1.42V
Zn2+ + 2e ---> Zn E = -0.76V

Ecell = -1.42 + (-0.76) = -2.18V

 

[spikers220]

I think what you are forgetting is that you solved it for the spontaneous net reation of:

Au3+ + Zn --> Au + Zn2+ E net = +2.18

But you dont have that case....You have the opposite reaction...

Au + Zn2+ --> Au3+ + Zn so your E net is -2.18

This should help your understanding...

Electrode potentials are :
Zn --> Zn2+ + 2e E=+0.76V
Au --> Au3+ + 3e E=-1.42V
If a gold foil were placed in a solution containing zinc ions, what would be the reaction potential.

The answer is -2.18V... But I got +2.18V

How would we know what is reduced/oxidized in this case?
I said that the Zn was oxidized and Au was reduced because the Ecell would be positive in that fashion.

Am I wrong? :/

 

[predentlove]

you guys are incredible

thanks so much for the help, future dentists 🙂