2014 Midterm Question 3

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604805638
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Joined: Wed Sep 21, 2016 2:59 pm

2014 Midterm Question 3

Postby 604805638 » Tue Mar 14, 2017 11:24 am

For this question we have to pick which chemicals to use for the galvanic cell and the correct answer says to pick Zn and Fe(NO3) would it be wrong we chose to do the galvanic cell with Zn and Cu(NO3)2?

Rochelle Ellison 2H
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Joined: Wed Sep 21, 2016 3:00 pm

Re: 2014 Midterm Question 3

Postby Rochelle Ellison 2H » Tue Mar 14, 2017 6:32 pm

Yes you would have to choose the chemicals containing Zn and Fe in order to get full credit. To determine this you would have to look at the standard reduction potentials of Zn+2, Cu+2, Fe+2, and Fe+3 to determine the one with the lowest reduction potential and the one with the highest reduction potential. This is because the question asks you to create a galvanic cell that will produce the highest possible voltage and you can do this by using the strongest oxidizing agent (Fe+3 to Fe+2 which has the highest reduction potential of 0.77V) and the strongest reducing agent (Zn(s) (written as the half reaction Zn+2 to Zn)which has the lowest reduction potential of -0.76V). The Zn half reaction has the lower reduction potential therefore Zn is the species being oxidized and the Fe half reaction has the higher reduction potential so Fe+3 is the species being reduced. After flipping the sign of the reduction potential of the Zn half reaction to represent the cell potential of the oxidation reaction and adding the reduction potential of the Fe+3 to Fe+2 half reaction you would have calculated (1.53V) the highest possible voltage that any combination of the given chemicals could have produced in a galvanic cell.

Camille_Rousculp_3A
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Joined: Wed Sep 21, 2016 3:00 pm

Re: 2014 Midterm Question 3

Postby Camille_Rousculp_3A » Thu Mar 16, 2017 3:22 pm

How would you know the reduction potential for these? Would they be given? Or is there another way to know?

Khachik_Hmayakyan_2E
Posts: 25
Joined: Sat Jul 09, 2016 3:00 am

Re: 2014 Midterm Question 3

Postby Khachik_Hmayakyan_2E » Fri Mar 17, 2017 12:39 pm

If I am not mistaken, the reduction potentials and any other necessary information will be provided on the back of the equation sheet. The equation sheets for each individual exams have been omitted and replaced with a general equation sheet at the beginning of the practice exams section. You can still determine the reduction potentials by looking at the appendix in the back of the textbook.


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