October 15, 2019, 07:20:59 AM
Forum Rules: Read This Before Posting


Topic: Electrochemistry Questions  (Read 4564 times)

0 Members and 1 Guest are viewing this topic.

Offline ///

  • Regular Member
  • ***
  • Posts: 31
  • Mole Snacks: +0/-1
Electrochemistry Questions
« on: December 09, 2006, 12:22:08 PM »
I just want to confirm a few anyways with you guys. I did them all on my own, but I want to make sure they're correct, I almost understand the unit so these questions weren't so bad, but still...confirming is good =)

1) Galvanic Cell notation: copper electrode in copper (II) sulfate solution and iron electrode in iron (II) nitrate sol'n.

I got: Fe(s) | Fe-2(aq) || Cu-2 | Cu (s)

My own question: how do we know which one gets reduced and which one gets oxidized? Do I look to see whether which one has the lowest Standard Reduction, and that would be the anode?

2) Shorthand representation using galvanic cell notation:
Reduction: MnO4- + 8H+(aq) + 5e- > Mn2+(aq) + 4H2O(l)
Oxidization: 2I- (aq) > I2 + 2e-


Anyways, I got
I2(s) | I-(aq) || MnO4- , Mn2+(aq) | Pt

3) Standard cell potential for Cu2+(aq) + Mg(s) > Mg2+(aq) + Cu(s)

I got
2.714V


For
Pb2+(aq) + Zn(s) > Pb(s) + Zn2+(aq)
I got 0.636V

Almost done...

4) 1M aqueous solution of NaBr is being electrolyzed...predict the products

So, for the possibilities and their Ecell: i got

1) Br and hydrogen: -1.48V
2) Br and Na: -3.777
3) Na and Oxygen: -3.526
4) Oxygen and Hydrogen: -1.229

Please confirm the individual cell potentials as well, not just the final product that I'm predicting.. which is Oxygen and Hydrogen.


One last question.

5) Current needed to deposit Nickel (10.0g) from a soln of NiSO4 (time: 40 mins)
I got 13.67Amps.

Correct?

Thanks in advance!

(I did it all on my own :D)
« Last Edit: December 09, 2006, 01:51:19 PM by /// »

Offline sdekivit

  • Chemist
  • Full Member
  • *
  • Posts: 403
  • Mole Snacks: +32/-3
  • Gender: Male
  • B.Sc Biomedical Sciences, Utrecht University
Re: Electrochemistry Questions
« Reply #1 on: December 09, 2006, 05:50:35 PM »
I just want to confirm a few anyways with you guys. I did them all on my own, but I want to make sure they're correct, I almost understand the unit so these questions weren't so bad, but still...confirming is good =)

1) Galvanic Cell notation: copper electrode in copper (II) sulfate solution and iron electrode in iron (II) nitrate sol'n.

I got: Fe(s) | Fe-2(aq) || Cu-2 | Cu (s)

My own question: how do we know which one gets reduced and which one gets oxidized? Do I look to see whether which one has the lowest Standard Reduction, and that would be the anode?

Fe(s) --> Fe(2+) and Cu(2+) --> Cu(s) just read from left to right. The solution is in the middle:

electrode | M | solution(electrolytes) | M | electrode

the || denotes a salt bridge.

2) Shorthand representation using galvanic cell notation:
Reduction: MnO4- + 8H+(aq) + 5e- > Mn2+(aq) + 4H2O(l)
Oxidization: 2I- (aq) > I2 + 2e-


Anyways, I got
I2(s) | I-(aq) || MnO4- , Mn2+(aq) | Pt

I2 as an electrode is impossible. I guess Pt is the electrode there too, so it would be slightly different.

3) Standard cell potential for Cu2+(aq) + Mg(s) > Mg2+(aq) + Cu(s)

I got
2.714V


For
Pb2+(aq) + Zn(s) > Pb(s) + Zn2+(aq)
I got 0.636V

Almost done...

correct

4) 1M aqueous solution of NaBr is being electrolyzed...predict the products

So, for the possibilities and their Ecell: i got

1) Br and hydrogen: -1.48V
2) Br and Na: -3.777
3) Na and Oxygen: -3.526
4) Oxygen and Hydrogen: -1.229

Please confirm the individual cell potentials as well, not just the final product that I'm predicting.. which is Oxygen and Hydrogen.

seems correct too --> didn't check the potentials.

5) Current needed to deposit Nickel (10.0g) from a soln of NiSO4 (time: 40 mins)
I got 13.67Amps.

Quote

correct too (i got 13,7 A)

Offline ///

  • Regular Member
  • ***
  • Posts: 31
  • Mole Snacks: +0/-1
Re: Electrochemistry Questions
« Reply #2 on: December 11, 2006, 04:14:59 PM »
I just want to confirm a few anyways with you guys. I did them all on my own, but I want to make sure they're correct, I almost understand the unit so these questions weren't so bad, but still...confirming is good =)

1) Galvanic Cell notation: copper electrode in copper (II) sulfate solution and iron electrode in iron (II) nitrate sol'n.

I got: Fe(s) | Fe-2(aq) || Cu-2 | Cu (s)

My own question: how do we know which one gets reduced and which one gets oxidized? Do I look to see whether which one has the lowest Standard Reduction, and that would be the anode?

Fe(s) --> Fe(2+) and Cu(2+) --> Cu(s) just read from left to right. The solution is in the middle:

electrode | M | solution(electrolytes) | M | electrode

the || denotes a salt bridge.

No, because they gave us the electrodes and the electrolytes...we have to determine the cell notation for it..
I wanted to know how we can determine which is oxidized and which is reduced.
What I did is I looked at the reduction potentials, and whichever one had the lower potential was oxidized. I didnt switch the signs if the reaction was oxidized, did I do it correctly?


Offline DevaDevil

  • Chemist
  • Full Member
  • *
  • Posts: 690
  • Mole Snacks: +55/-9
  • Gender: Male
  • postdoc at ANL
Re: Electrochemistry Questions
« Reply #3 on: December 12, 2006, 04:17:44 PM »
E (cell) = E (cathode) - E (anode) = positive.

That is how you define cathode and anode. If your E (cell) = negative, you have assigned anode and cathode wrong.

Lowest E = oxidation = anode

Sponsored Links