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Reducing agents, question

arc5005

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    Which of the following species is the strongest reducing agent?

    A. Cl2
    B. Cu
    C. Mg2+
    D. Zn

    D) Zn
    Reducing agents get oxidized, so we need to reverse the reactions in table 4.1. This eliminates choices A & C, because Cl2 and Mg2+ cannot oxidize further. Between Zn and Cu, the more favorable oxidation (reverse reaction from table 4.1) is found with zinc (0.76 > -0.34)

    IMG_2792.jpg



    My question:
    So Cl2 can't be oxidized because it's stable as a diatomic molecule?
    And I'm assuming Mg2+ because it has reached noble gas configuration (this one makes sense to me), but if you didn't realize those, and just based it off the table above, then you'd make the mistake of picking Mg2+ as the answer.
     

    Lawpy

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      A strongest reducing agent is one that is most easily oxidized. Oxidation refers to loss of electrons or an increase in oxidation state. The reduction potential tables commonly seen and provided refer to how easily reduced a particular chemical entity is. So to find what’s the best reducing agent, you would need to reverse the half-reactions to see the loss of electrons, and you compare the resulting voltage values (remember to flip the sign since you are reversing the reaction).

      For this question, Cl2 and Mg2+ are already fully oxidized. You can’t remove any more electrons since they already have a stable octet (not to mention chlorine is unstable under a positive charge unless it’s bonded with an even more electronegative atom like fluorine).

      But Cl2 can accept an electron since it likes to have a negative charge, which is why Cl2 is a good oxidizing agent and its reduction potential is positive. Mg2+ however doesn’t want electrons since adding electrons will force it to use its 3s orbital which requires energy. That’s why Mg2+ reduction potential is strongly negative. On the flip side, Mg is happy to lose its 3s electrons to become a stable Mg2+ ion with an octet filled at lower energy levels, which is why Mg is a good reducing agent with a positive oxidizing potential (it’s the reverse of Mg2+ reduction potential).

      Comparing the reverse of the half-reactions of Zn and Cu readily shows that Zn has a higher oxidizing potential than Cu and is thus a better reducing agent.
       
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      arc5005

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        11-table-01.gif


        A strongest reducing agent is one that is most easily oxidized. Oxidation refers to loss of electrons or an increase in oxidation state. The reduction potential tables commonly seen and provided refer to how easily reduced a particular chemical entity is. So to find what’s the best reducing agent, you would need to reverse the half-reactions to see the loss of electrons, and you compare the resulting voltage values (remember to flip the sign since you are reversing the reaction).

        For this question, Cl2 and Mg2+ are already fully oxidized. You can’t remove any more electrons since they already have a stable octet (not to mention chlorine is unstable under a positive charge unless it’s bonded with an even more electronegative atom like fluorine).

        But Cl2 can accept an electron since it likes to have a negative charge, which is why Cl2 is a good oxidizing agent and its reduction potential is positive. Mg2+ however doesn’t want electrons since adding electrons will force it to use its 3s orbital which requires energy. That’s why Mg2+ reduction potential is strongly negative. On the flip side, Mg is happy to lose its 3s electrons to become a stable Mg2+ ion with an octet filled at lower energy levels, which is why Mg is a good reducing agent with a positive oxidizing potential (it’s the reverse of Mg2+ reduction potential).

        Comparing the reverse of the half-reactions of Zn and Cu readily shows that Zn has a higher oxidizing potential than Cu and is thus a better reducing agent.


        Thank you. :)
         
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