2014 Winter Final

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Fengting Liang 1F
Posts: 23
Joined: Sat Jul 09, 2016 3:00 am

2014 Winter Final

Postby Fengting Liang 1F » Sat Mar 18, 2017 5:42 pm

Can someone explain for Q3 part A, why each chemical is selected to be part of the galvanic cell (or why not)?
page 182 in course reader

Audrey Magsig 1E
Posts: 17
Joined: Wed Sep 21, 2016 3:00 pm

Re: 2014 Winter Final

Postby Audrey Magsig 1E » Sat Mar 18, 2017 6:46 pm

Unfortunately for this question we are missing a table of reduction potentials. For this question, we are trying to build a galvanic cell that has the highest overall voltage. Here are the missing reduction potentials:

Zn (2+) + 2e -> Zn (s) -.763V

Fe (2+) + 2e -> Fe (s) -.44V

Fe (3+) + e -> Fe (2+) (aq) .771

Cu (+) + e -> Cu (s) .521V


So in creating the galvanic cell we want to choose the two that combined give the greatest overall voltage which, using the E*cell= E*cathode- E*anode, would be the reduction of Zinc to Zn(s) and Fe (3+) to Fe (2+) (in the equation: .771- (-.763) which would give an overall cell potential of 1.534). As the reduction of iron is to another aqueous iron ion, we use Fe(NO3)2 instead of Fe(s) which implies that we also need to use Pt as a conductor.

Therefore, we use Zn(s), Zn(NO3)2, Fe(NO3)2, Fe(NO3)3, and Pt in the reaction.

Fengting Liang 1F
Posts: 23
Joined: Sat Jul 09, 2016 3:00 am

Re: 2014 Winter Final

Postby Fengting Liang 1F » Sat Mar 18, 2017 7:54 pm

Why couldn't we use solid Fe as a conductor?

Chem_Mod
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Re: 2014 Winter Final

Postby Chem_Mod » Sat Mar 18, 2017 8:25 pm

Fengting Liang 1F wrote:Why couldn't we use solid Fe as a conductor?


Unwanted reactions with Fe(s) and the other two iron species.


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