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Topic: Electron-transfer reactions  (Read 508 times)

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Offline Win,odd Dhamnekar

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Electron-transfer reactions
« on: November 12, 2021, 05:54:35 AM »
My Answers:
(a) All ion concentrations are 1.0 M, so E° values may be used. E°cell= Ered - Eox= E°Pt - E°Cr = 0.17 V  - (-0.74 V)= +0.91 V

(b) At equilibrium, there is no driving force for the reaction and ΔG reaches zero. Therfore measured potential at equilibrium will be 0 V.

(c) The Cr3+ would  be coverted to Cr causing chromium solution to decrease in charge, while the Pt° metal would become Pt+ increasing the charge on SO42-, H+, H2SO3 solution. Unless these charges were balanced by ion flow from or to the salt bridge, electrons would no longer flow away from Chromium solution to the SO42-,H+, H2SO3 solution and the reaction would cease.

(d) I would predict the increase in mass would happen to the mass of Platinum electrode as the reaction proceeded in the spontaneous direction.

(e)Chromium  electrode is the anode and Platinum electrode is the cathode.


Are all the above-mentioned my answers to the questions asked correct? Let me know. Thanks for reading and interpreting my answers.
 
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Offline mjc123

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Re: Electron-transfer reactions
« Reply #1 on: November 12, 2021, 08:25:06 AM »
The Pt is an inert electrode; the redox reaction here is between sulfate and sulfite. In fact I think that's what you've used (0.17 V), but don't call it E°Pt.
Are you told the concentrations are 1M?
There is no copper electrode, is that a misprint?

Offline Win,odd Dhamnekar

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Re: Electron-transfer reactions
« Reply #2 on: November 13, 2021, 10:45:48 AM »
What do you call the redox reaction between SO42- and H2SO3 if it is not E°Pt?

Yes, There is misprint. In this electrochemical cell, no copper electrode is used.

Are my answers to (a), (b), (c), (d) and (e)  correct?
Any science consists of the following process.
 1) See 2) Hear 3) Smell if needed 4) Taste if needed
5) Think 6) Understand 7) Inference 8) take decision [Believe or disbelieve, useful or useless, healthy or unhealthy, cause or effect, favorable or unfavorable, practical or theoretical, practically possible or practically impossible, true or false or  any other required criteria]

Offline mjc123

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Re: Electron-transfer reactions
« Reply #3 on: November 13, 2021, 03:21:35 PM »
Not all. Write out the full cell equation for the spontaneous reaction. This may help you.

Offline Win,odd Dhamnekar

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Re: Electron-transfer reactions
« Reply #4 on: November 16, 2021, 01:56:09 AM »
1)Cr3+ + 3e- :rarrow: Cr E° -0.74 V

2) SO42- + 4H+ + 2e- :rarrow: H2SO3 + H2O E° 0.17 V

Or do you mean to say the following equation for spontaneous reaction between Cr3+ and SO42-?

Cr2O72- + 3SO32- + 8H+  :rarrow: 2Cr3+ + 3SO42- + 4H2O(l)
Any science consists of the following process.
 1) See 2) Hear 3) Smell if needed 4) Taste if needed
5) Think 6) Understand 7) Inference 8) take decision [Believe or disbelieve, useful or useless, healthy or unhealthy, cause or effect, favorable or unfavorable, practical or theoretical, practically possible or practically impossible, true or false or  any other required criteria]

Offline mjc123

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Re: Electron-transfer reactions
« Reply #5 on: November 16, 2021, 06:26:29 AM »
No. Where do you get the dichromate from? That reaction is spontaneous in the direction written; Cr3+ and SO42- won't make Cr2O72- and SO32-.
Take your half-equations 1 and 2; combine them to make the full equation for the cell reaction, written in the spontaneous direction. Where is oxidation taking place, and where is reduction? So which electrode is the anode and which the cathode?

Offline Win,odd Dhamnekar

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Re: Electron-transfer reactions
« Reply #6 on: November 16, 2021, 10:23:19 AM »
 Full cell equation for the spontaneous reaction:
2Cr + 3SO42- + 12H+  :rarrow: 2Cr3+ + 3H2SO3 + 3H2O

Chromium is oxidized and sulfur is reduced. Chromium electrode  is anode and Platinum electrode immersed in sulfate, sulfurous acid solution   is cathode

Revised answer to (c): The Cr electrode would be converted to Cr3+ causing chromium solution to increase in charge while platinum metal would remain inert. Unless these charges were balanced by ion flow from or to the salt bridge, electrons would no longer flow away from Chromium solution to the SO42-,H+, H2SO3 solution and the reaction would cease.

Revised answer to (d): The Platinum would remain inert. So no increase takes place in its mass.

I think answers to (a), (b) and (e) are correct.
 
Any science consists of the following process.
 1) See 2) Hear 3) Smell if needed 4) Taste if needed
5) Think 6) Understand 7) Inference 8) take decision [Believe or disbelieve, useful or useless, healthy or unhealthy, cause or effect, favorable or unfavorable, practical or theoretical, practically possible or practically impossible, true or false or  any other required criteria]

Offline mjc123

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Re: Electron-transfer reactions
« Reply #7 on: November 16, 2021, 05:19:52 PM »
I think your answers are correct now.

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