Quick question about Electrochemistry anode and cathode

[qpham26]

Homework Statement

Pb/Pb²⁺ and Ag/Ag⁺

Ni/Ni²⁺ and Zn/Zn²⁺
Which one is the anode and cathode?
Toward which metal do the electrons flow?

The Attempt at a Solution

2Ag²⁺ + Pb ⇔ 2Ag + Pb²⁺

Pb is anode
and Ag is cathode

e^- go toward Ag.


Zn + Ni²⁺ ⇔ Zn²⁺ + Ni

Zn is anode
and Ni is cathode

e^- go toward Ni.
Is this correct?

Thanks.

 

[kvnstv1]

Unfortunately, you got them backwards in both cases.

Remember reduction (increase in number of electrons) occurs at the cathode while oxidation occurs at the anode. So check which of the elements is more electropositive. That element will form your anode. The periodic table will help you.

 

[qpham26]

I don't understand, i used the same method for other problems and I got right answer.
This is what I did.
because for Pb/Pb2+ and Ag/Ag+
the standard reduction at 25 C

Pb²⁺ + 2e^-⇔Pb(s) E = -0.13
Ag⁺+e^-⇔Ag(s) E = 0.80

So flip top eq to get an oxidation of Pb and Ag is already in reduction form
so ox = anode
and red = cathode?

so total E = 0.80 + 0.13 = 0.93

thanks for your time.

 

[Borek]

2Ag²⁺ + Pb ⇔ 2Ag + Pb²⁺

Almost correct. Ag is not 2+, but I assume it is just a typo.

Zn + Ni²⁺ ⇔ Zn²⁺ + Ni

Correct.

Although you should use → in both cases.

 

[qpham26]

Almost correct. Ag is not 2+, but I assume it is just a typo.



Correct.

Although you should use → in both cases.

Yes it was a typo.
And since it is correct we can see that
Pb lost electron so it is the anode?

same goes for the other case.