Test 2 Question 5

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Ethan-Van To Dis2L
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Joined: Fri Sep 29, 2017 7:05 am

Test 2 Question 5

Postby Ethan-Van To Dis2L » Wed Mar 14, 2018 1:14 am

They asked to rank Zn, Mn, Cr in order of reducing power.
Zn+2 + 2e- = -0.76 V
Mn+2 + 2e- = -1.18 V
Cr+3 + 3e- = -0.74 V

So I ranked them as Mn>Zn>Cr but the answer was the reverse of that. Can someone explain why am wrong? From my understanding, for a species to have a lot of reducing power, it would be very likely to be oxidized. So I thought Mn would have the greater reducing power cause the above equation shows the reduction of Mn, and since it is more negative than everything else, it would less likely to be reduced and more likely to be oxidized thus having more reducing power.

Julian Krzysiak 2K
Posts: 49
Joined: Fri Sep 29, 2017 7:07 am

Re: Test 2 Question 5

Postby Julian Krzysiak 2K » Wed Mar 14, 2018 2:10 am

Your logic is correct, Mn has the most reducing power. But the question asks to put them in order of increasing reducing power, which means you have to order them from worst reducing power to best reducing power. The way you wrote it is technically correct, with the inequality signs, Mn>Zn>Cr. If you put them with inequality signs like that on the test, you should have gotten credit, but maybe they are specifically looking for putting them in increasing order w/o any inequality signs.

Ammar Amjad 1L
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Joined: Thu Jul 27, 2017 3:00 am
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Re: Test 2 Question 5

Postby Ammar Amjad 1L » Wed Mar 14, 2018 8:04 am

Hey, so the potential you've written for Cr should be -0.91 V, the one you've written is the potential for Cr^3+ going to Cr, you need to use the potential from Cr^2+ to Cr. Hope this helps.
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