Balancing redox reactions occurring in acidic solutions

[shikam08]

Homework Statement

Balance the following redox reactions occurring in an acidic solution.

Homework Equations

PbO₂(s)+I^-(aq)---->Pb²⁺(aq)+I₂(s)

The Attempt at a Solution

1.) half reactions:
a.) reduction: I^-(aq)----->I₂(s)
b.) oxidation: PbO₂(s)------>Pb²⁺(aq)
2.) balance Oxygens and Hydrogens
PbO₂+4H⁺------>Pb²⁺+2H₂O
3.) add electrons to balance equations
a.)PbO₂+4H⁺+4e^---->Pb⁺²+2H₂O
b.) 4I--->4I₂+4e^-
4.) cancel out the electrons and combine the half reactions
PbO₂+4H⁺+4I--->Pb²⁺+4I₂+2H₂O

 

[Borek]

b.) 4I--->4I₂+4e^-

Nope.

 

[shikam08]

I don't understand how to insert the number of electrons on both sides to balance the equations and cancel out the electrons.

 

[Borek]

Balance atoms first, then use electrons to balance charge in half reaction. As long as charge on both sides is different, equation is not balanced.