strongest reducing agent

[adrakdavra]

Which of the following is the strongest reducing agent?

Electrochemical reaction Eo value (V)
MnO2 + 4H+ + 2e- ↔ Mn2+ + 2H2O +1.23
Fe3+ + e- ↔ Fe2+ +0.771
N2 + 5H+ + 4e- ↔ N2H5+ -0.230
Cr3+ + e- ↔ Cr2+ -0.410


A. Cr3+
B. Cr2+
C. Mn2+
D. MnO2
INCORRECT:
Your Answer: C
Correct Answer: B Why???😎

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[GomerPyle]

Which of the following is the strongest reducing agent?

Electrochemical reaction Eo value (V)
MnO2 + 4H+ + 2e- ↔ Mn2+ + 2H2O +1.23
Fe3+ + e- ↔ Fe2+ +0.771
N2 + 5H+ + 4e- ↔ N2H5+ -0.230
Cr3+ + e- ↔ Cr2+ -0.410


A. Cr3+
B. Cr2+
C. Mn2+
D. MnO2
INCORRECT:
Your Answer: C
Correct Answer: B Why???😎

Strongest reducing agent is one that is oxidized most readily (and thus has the highest oxidation potential). The Eo values given are reducing potentials (since the reactions are written from left to right as reductions), so you need to reverse the sign and look at the reactions from right to left for oxidation (losing electrons).

A. Cr3+ is reduced, not oxidized. Therefore not a reducing agent.

B. Cr2+ is oxidized in the reaction and has an oxidizing potential of +0.410

C. Mn2+ is oxidized in the reaction and has an oxidizing potential of -1.23

D. MnO2 is reduced, not oxidized. Therefore not a reducing agent.

You can see that Cr2+ has the strongest oxidizing potential, and therefore is the strongest reducing agent.

 

[adrakdavra]

Strongest reducing agent is one that is oxidized most readily (and thus has the highest oxidation potential). The Eo values given are reducing potentials (since the reactions are written from left to right as reductions), so you need to reverse the sign and look at the reactions from right to left for oxidation (losing electrons).

A. Cr3+ is reduced, not oxidized. Therefore not a reducing agent.

B. Cr2+ is oxidized in the reaction and has an oxidizing potential of +0.410

C. Mn2+ is oxidized in the reaction and has an oxidizing potential of -1.23

D. MnO2 is reduced, not oxidized. Therefore not a reducing agent.

You can see that Cr2+ has the strongest oxidizing potential, and therefore is the strongest reducing agent.

Thanks, I also realized this afterward, that the most negative on the reduction table is the most oxidized, so by looking at the table Cr2+ is the one. it is easy to spot it when they are all listed as reducing potentials
However, if they were listed by oxidizing potentials then I have to figure out which one is most oxidized and look at the most positive number , am I at the right track ?😎

 

[GomerPyle]

Thanks, I also realized this afterward, that the most negative on the reduction table is the most oxidized, so by looking at the table Cr2+ is the one. it is easy to spot it when they are all listed as reducing potentials
However, if they were listed by oxidizing potentials then I have to figure out which one is most oxidized and look at the most positive number , am I at the right track ?😎

Yep, you are right. A trick that the MCAT likes to do is write both reduction and oxidation potentials in the same column, so what you have to do is go to the reaction and see if the forward reaction is an oxidation or reduction reaction. If it is an oxidation reaction, then the corresponding potential value written next to it will be an oxidation potential and not a reduction potential, and vice versa.