How Do You Calculate the Redox Potential for This Reaction?

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Discussion Overview

The discussion revolves around calculating the redox potential for a specific chemical reaction involving chromium and iodine compounds. Participants explore the use of the Nernst equation, the interpretation of half-cell potentials, and the correct symbols for elements involved in the reaction.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant calculates the redox potentials for the half-reactions using the Nernst equation and questions whether the overall redox potential is the sum of these potentials.
  • Another participant clarifies that the Nernst equation is typically used to find the overall redox potential rather than half-cell potentials, suggesting a need to reference standard half-cell potential tables.
  • There is a discussion about the use of the symbol "J" for iodine, with some participants noting it was historically used but may be considered a typo in this context.
  • A participant seeks clarification on how to calculate the standard potential (Eo) and whether it should be based on the pair that exchanges electrons or between different pairs in the reaction.

Areas of Agreement / Disagreement

Participants express differing views on the application of the Nernst equation and the interpretation of half-cell potentials. There is no consensus on the correct approach to calculating the overall redox potential or the correct notation for iodine.

Contextual Notes

Some assumptions about the use of the Nernst equation and the identification of elements may not be fully resolved. The discussion includes references to standard half-cell potentials and the need for accurate chemical notation.

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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