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E Cell Potential. Mysterious -1.05


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#1 Blank03

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Posted 19 February 2018 - 10:14 PM

Hi good day!
just want to ask this one.
I dunno if its me or my research ability is not enough but...
how come this Mn equals to -1.05??
I had been searching all standard potential values at 298K (starting from Atkins) and all they giving me is -1.18.
i tried to compute it and the value is giving me is around 0.47 to 0.48.
on our slide it goes with 0.6.its all because of that -1.05 value.
 
can you help me out on this one cuz really, I did all that I can but its giving me -1.05 for cell potential of E.
AM i wrong?
thank you so much.
I am not confident on my answer cuz u know, its my professor's answer after all.
Maybe there is some trick or whatsoever but I cant really find it.
 
here is the picture. thank you guys!!!
 
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#2 MrShorty

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Posted 20 February 2018 - 02:26 PM

As near as I can tell, your use of the Nernst equation looks correct. I cannot say where your professor is getting the E0 of 1.05 for the Mn half reaction. In an old text, I found an E0 for a Mn(CN) complex that is 1.05 -- is it possible that he/she accidentally pulled the wrong value from his/her table of standard reduction potentials? Can you approach the professor or an assistant or someone to ask where that comes from?

 

The point of the exercise is to demonstrate how well you can use the Nernst equation -- including looking up reduction potentials in a table. I would suggest that you use the values you believe to be correct, document where the values are coming from, and proceed to compute the voltage from the Nernst equation. If you cannot approach the professor before submitting the test/assignment, I would suggest that you pick what you believe is the correct answer, document you work to show why you think it is correct, and then see what feedback you get.



#3 breizh

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Posted 21 February 2018 - 06:31 AM

Hi,

Lange's Chemistry Handbook : -1.17 V at 25C for Mn2+/Mn  half reaction.

Breizh






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