I don't understand the answer of this redox multiple choice question?

The question is "Find the total of all the coefficients in the balanced equation when 1 mol of MnO4- is reduced."

The unbalanced equation provided reads:

MNO4- + H+ + e- -----> Mn2+ + H2O

The options are:

A. 5

B. 9

C. 17

D. 19

Why is the correct answer D? Shouldn't it be C?

Please explain. Thanks!

2 Answers

  • Yash
    Lv 5
    6 years ago
    Best Answer

    The unbalanced equation provided reads:

    MnO4- + H+ + e- -----> Mn2+ + H2O

    To balance it, you need to balance charge and mass.

    Mn is already balanced so we move on to electrons. Now since the Mn atom takes up five electrons in being reduced, you can write 5 as the co-efficient.Now we have:

    MnO4- + H+ + 5e- -----> Mn++ + H2O

    The charge on RHS is (+2) and will not change. So to balance the charge on LHS you have to have 8H+:

    MnO4- + 8H+ + 5e- -----> Mn++ + H2O

    Now just balance the H2O:

    MnO4- + 8H+ + 5e- -----> Mn++ + 4H2O

    The co-efficients are 1,8,5,1,4 so the sum is 19.

  • 6 years ago

    The balanced half equation is: 1 MnO4- + 8 H+ 5 e- ------>1 Mn++ + 4 H2O

    Total is 1+8+5+1+4 =19

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