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Topic: why does fe dissolve in 1.0 M Ce4+?  (Read 1234 times)

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Offline jchoi

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why does fe dissolve in 1.0 M Ce4+?
« on: June 03, 2018, 02:08:23 AM »
Hi, I have a question about electrochemistry. Will Fe dissolve in 1.0M Ce4+? If so, will Fe3+ or Fe2+ be formed?
I think I have to use E°=0.0592/n(logK) to solve this question, but I'm not sure what the value of n would be. I have the answer (Yes, and Fe2+), but would like to understand how I can arrive at that answer.

This is my first post, so feel free to let me know if there's a rule I should abide by!

Offline Borek

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Re: why does fe dissolve in 1.0 M Ce4+?
« Reply #1 on: June 03, 2018, 03:14:01 AM »
Start by listing all related E0 potentials.
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Offline jchoi

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Re: why does fe dissolve in 1.0 M Ce4+?
« Reply #2 on: June 03, 2018, 10:25:12 AM »
E° of Fe2+ = -0.41V
E° of Fe3+ = -0.04V

Since the question is asking for Fe(s) dissolving in a Ce4+ solution, I think I can reverse (take the negative of) these values to have 0.41V and 0.04V.

Offline Borek

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Re: why does fe dissolve in 1.0 M Ce4+?
« Reply #3 on: June 03, 2018, 01:38:48 PM »
You have omitted two other important potentials.

Hint: oxidation goes in two steps, and there is also reduction involved.

No, you don't change the sign of the potential when the reaction goes in the opposite direction.
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Offline jchoi

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Re: why does fe dissolve in 1.0 M Ce4+?
« Reply #4 on: June 03, 2018, 02:22:19 PM »
I think I need potentials for Ce4+ and Ce3+ but I can't find those potentials chart I have, or in other charts online. Or are the potentials from Fe3+ :rarrow: Fe2+ + e-?

Two steps as in Fe(s) :rarrow: Fe3+ :rarrow: Fe2+?

Offline Borek

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Re: why does fe dissolve in 1.0 M Ce4+?
« Reply #5 on: June 03, 2018, 02:36:26 PM »
I think I need potentials for Ce4+ and Ce3+ but I can't find those potentials chart I have, or in other charts online.

Not for both of them, you need potentials for Ce4+ :rarrow: Ce3+ reduction. That's what will be happening in the solution.


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Or are the potentials from Fe3+ :rarrow: Fe2+ + e-?

This is as wrong as it can be (check if the charges are balanced ;) )  but you are in general on the right track.

Quote
Two steps as in Fe(s) :rarrow: Fe3+ :rarrow: Fe2+?

Wrong order, but yes, it is about stepwise oxidation of Fe, not an oxidation followed by a reduction.
« Last Edit: June 03, 2018, 04:05:36 PM by Borek »
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