2010 DAT destroyer gen chem # 32 problem

[Solapike]

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I've been trying to comprehend why the book got the answer they did. If anyoen can explain I would be appreciative.

32. How many H+ would be needed to balance the following redox reaction?

MnO4- + I- --> I2 + MnO2 + H2O

a) 8
b)6
c)5
d)4
e)3

The book says the answer is A but I'm only getting 4H+ (D)

The books reasoning is

2I- --> I2 + 2e-
4H+ + 3e- + MnO4- -->MnO2 + 2H2O (how are they getting 3e- I'm only getting 2e-).

Any help would be awesome thanks!

 

[kevinrho]

Someone can correct me if I'm wrong. Maybe another SDNer will contribute as well.... but... here we go....

I think the problem where you are confused lies here.....

4H+ + 3e- + MnO4- -->MnO2 + 2H2O (how are they getting 3e- I'm only getting 2e-).

MnO4- = Mn (7+).....O4(😎

MnO2 = Mn(4+)......O2(4-)

This is why they are getting 3e-..... Mn(7+) was reduced by 3e- in order to get Mn(4+)

Original equation: MnO4- + I- + H+ --> I2 + MnO2 + H2O

Balance half reactions....
3e- + MnO4- + 4H+ -----> MnO2 + 2H2O

2I- ------> I2 + 2e-

Multiply by 2 on top...... 2(3e- + MnO4- + 4H+ -----> MnO2 + 2H2O)

you get.... 6e- + 2MnO4- + 8H+ -----> 2MnO2 + 4H2O

Multiply by 3 on bottom 3(2I- --------> I2 + 2e-)

you get 6I- ------> 3I2 + 6e-

there you go...... 8H+

hope i didn't confuse you....

 

[Solapike]

Thank you very much I get it now!