REDOX

[mandy]

Balance the following redox eqns by seperating them into two half eqns, balancing each eqn, and then combining the pair into a balanced complete redox equation.
a. H₂O₂(aq) + PbS(s) ------------>  PbSO₄(s) + H₂O(l)

There's a part a - f, but I think if I have some guidance on the first bit, I can do the rest
Anyone know what to do ?

[chem-nerd]

your two half equations would start with:
H2O2       -> H2O

PbS      ->   PbSO4

to balance each one, use the KOHeS method
K balance the key element (usually the element other than O or H)
O balance oxygen atoms by adding water
H balance hydrogen atoms by adding H+
e balance electrons
S ensure you have correct states

[mandy]

when i made the half eqns, i got :

H₂O₂ + 2H⁺ + 2e^-----> H₂O + H₂O

and

PbS + 4H₂O -----> PbSO₄ + 8H⁺ + 8e^-

So i multiplied the top eqn by 4, and then combined them to get :

4H₂O₂ + 8H⁺ + PbS + 4H₂O  -------> 8H₂O + PbSO₄ + 8H⁺

this is completely wrong

[chem-nerd]

don't forget to cancel out the H2O and H+ that appear on both sides

[mandy]

but there's 4H2O on one side, and 8 on the other :S

[chem-nerd]

so cancel 4 from both sides

[mandy]

oh thank you :DDDD

I have another qn,

List the following in order of increasing reducing strength:
Mg, I^-, Ag, F^-,Ni, Sn, Li, Cu

Do I just base this on the electrochemical series ?

[mandy]

Balance the following redox eqns by seperating them into two half eqns, balancing each eqn, and then combining the pair into a balanced complete redox equation.
a. H₂O₂(aq) + PbS(s) ------------>  PbSO₄(s) + H₂O(l)

Similar to this question, but this is part c.

SO₂^- + MnO₄^- ------> SO₃^2- + Mn²⁺

Nothing works :@