How Do You Calculate the Redox Potential for This Reaction?

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SUMMARY

The discussion focuses on calculating the redox potential for the reaction Cr2(SO4)3 + 4K2SO4 + 3I2 + 7H2O <=> K2Cr2O7 + 6KI + 7H2SO4 using the Nernst equation. The calculated half-cell potentials are -1.42V for the chromium reaction and 0.51V for the iodine reaction. Participants clarify that the overall redox potential is determined by the standard half-cell potentials and the number of electrons transferred, rather than simply summing the calculated potentials. The symbol "J" was identified as a typo for iodine, which is historically represented as "J" in older literature.

PREREQUISITES
  • Nernst equation for electrochemical calculations
  • Understanding of standard half-cell potentials
  • Knowledge of redox reactions and electron transfer
  • Familiarity with chemical notation and symbols
NEXT STEPS
  • Research standard half-cell potentials from electrochemical tables
  • Learn how to apply the Nernst equation to calculate overall redox potentials
  • Study the historical context of chemical symbols, particularly iodine
  • Explore the concept of electron transfer in redox reactions
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Chemistry students, educators, and professionals involved in electrochemistry or redox reaction analysis will benefit from this discussion.

vaazu
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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?
 
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vaazu said:
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.
 
eli64 said:
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.



 
eli64 said:
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.
 
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