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March 30, 2017

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What is n, the number of moles of electrons transferred, in the following reaction?

2 MnO4-(aq) + 16 H+(aq) + 10 Cl-(aq) ===> 2 Mn2+(aq) + 5 Cl2(g) + 8 H2O(l).

  • Gen Chem - ,

    Mn goes from +7 on the left to +1 on the right(per Mn atom).
    Cl goes from -1 on the left to zero on the right (for each Cl atom/ion). That is all but telling you the number for n.

  • Gen Chem - ,

    So is n=5 then? (7-1)+(-1-0)?
    or (7-1)+(|-1-0|) then n=7?

    My choices are 2, 4, 5, 10, 16...

  • Gen Chem - ,

    No. Five is not right.
    Notice EACH Mn goes from +7 to +2. That is a change of n = 5 FOR each Mn atom. How many Mn atoms undergo that change? Or look at Cl.
    EACH Cl^- goes from -1 to 0. You have ten of them undergoing that change (from 10Cl^- to 5Cl2). What is total n?

  • Gen Chem - ,

    so n=10 then, right? 2Mn atoms (2*5), and 1*10 for the Cl...?

  • Gen Chem - ,

    right.
    In a redox reaction, electrons lost must equation electrons gained. Each Mn gains 5 electrons (from +7 to +2) and there are two of them and 2 x 5 = 10 electrons gained.
    For Cl, we have 10 Cl^- (at -1 each) going to 5Cl2 (at zero each), which is 10 electrons lost.

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