help balance equation

[Farcus]

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you have H+ + MNO4- + Fe2+ -> MN2+ Fe3+ + H2O

why is the answer 8H+ MNO4- + 5Fe2+ -> Mn2+ 5Fe3+ + 4H20?

I get everything except the 5 iron.... why did they do that? it don't make any sense.

 

[bodonid]

you have H+ + MNO4- + Fe2+ -> MN2+ Fe3+ + H2O

why is the answer 8H+ MNO4- + 5Fe2+ -> Mn2+ 5Fe3+ + 4H20?

I get everything except the 5 iron.... why did they do that? it don't make any sense.

I will work the problem and get back to you, but my first instinct is to say they did it for charge balance.

 

[bodonid]

Yes, I assume you worked the problem to this point:

8H+ + MnO4- + Fe2+ -> Mn2+ + Fe+3 + 4H2O

The problem is that the left side has a charge of 9+ while the right has a charge of 5+, a difference of 4+. So unless you want the reaction to consume electrons, you have to use more iron. The balanced equation has a left side charge of 17+ and a right side charge of 17+, so they are equal.

 

[Farcus]

yeh I got there too but I was taught to balance charge you add the number of e-1 to the side that need it. 😱 never seen this kind of problem before I didn't know u can do that.

 

[bodonid]

yeh I got there too but I was taught to balance charge you add the number of e-1 to the side that need it. 😱 never seen this kind of problem before I didn't know u can do that.

DUDE! Go Dawgs!! I didn't notice you were from UGA before. I am an alum c/o 07. But yeah, you can add e-, but only in half reactions for redox. If you add e- to a complete chemistry equation, then the reaction is electrogenic and you need an electron acceptor.

 

[ecoli]

balance the half reactions and it should make sense.