• Support PF! Buy your school textbooks, materials and every day products Here!

Electrochemistry; redox potential

  • Thread starter vaazu
  • Start date
  • #1
21
0

Homework Statement



I have to calculate the redox potential of this equation:
Cr2(SO4)3 + 4K2SO4 + 3J2 +7H2O <=> K2Cr2O7 + 6KJ +7H2SO4
I used the nernst equation to calculate the potentials of
2Cr(3+)+7H2O -> Cr2O7(2-) +14H(+) +6e(-) and
I2 +2e(-) ->2J(-)
which were -1.42V and 0.51V, all ion concentrations were 0.1

Is the overall redox potential the sum of these potentials?
 

Answers and Replies

  • #2
133
0
1. Cr2(SO4)3 + 4K2SO4 + 3J2 +7H2O <=> K2Cr2O7 + 6KJ +7H2SO4
I used the nernst equation to calculate the potentials of
2Cr(3+)+7H2O -> Cr2O7(2-) +14H(+) +6e(-) and
I2 +2e(-) ->2J(-)
which were -1.42V and 0.51V, all ion concentrations were 0.1

Is the overall redox potential the sum of these potentials?


Are these J's typos, meaning I instead?

So you used the Nerst equation to calculate the half cell potentials? The Nerst equation is used to find the overall redox potential for the overall redox reaction, not half cell potential as implied here.

The standard half cell potentials for these half reactions are used (look up in a table) to calculate Eo, find the number of electrons transferred and use the 0.1 concentrations in the ions for the overall reaction.
 
  • #3
Borek
Mentor
28,328
2,717
Are these J's typos, meaning I instead?
Interesting. J was iodine symbol up to around 1980, it is used this way in older books.

So you used the Nerst equation to calculate the half cell potentials? The Nerst equation is used to find the overall redox potential for the overall redox reaction, not half cell potential as implied here.
It works both ways.



 
  • #4
21
0
Are these J's typos, meaning I instead?

The standard half cell potentials for these half reactions are used (look up in a table) to calculate Eo, find the number of electrons transferred and use the 0.1 concentrations in the ions for the overall reaction.
Yes the J was typo, it should be I. Don´t know what was I thinking. Could you explain me, how the Eo is calculated, or what should I be looking for? Is the reaction standard potential calculated between the pair which actually exchanged electrons Cr(3+) and I2, or somehow between the chrome and iodide pairs.
 
Last edited:

Related Threads for: Electrochemistry; redox potential

  • Last Post
Replies
6
Views
1K
  • Last Post
Replies
1
Views
2K
Replies
2
Views
4K
Replies
1
Views
1K
Replies
1
Views
599
Replies
0
Views
2K
Replies
4
Views
10K
Replies
0
Views
2K
Top