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# Help with balancing Redox Equations watch

1. I'm not asking anyone to do my homework for me I'm just stuck and confused on how to balance equations especially when the electrons are not the same for example in one part its 2e- and in the other part its 6e- for example how would you get them the same? If that makes sense. Could someone go through a step by step on how to do it for the first one only please as an example? The equation is Pbo2 --> Pb 2+ , Cl- --> cl2
2. [A] PbO2 --> Pb2+
[B] Cl- --> Cl2

These are the two you are combining. Usually, you'd be told whether these are in acid or basic conditions, for the purpose of balancing. In acid conditions, you are allowed to use H+ and H2O to balance things. In basic conditions, you are allowed to use OH- and H2O to balance. I will assume acid conditions, corresponding to the dissolution and reaction of PbO2 in HCl(aq)

[A]

As these are redox equations, the first step is to look at the oxidation state of Pb in the product and reactant.
PbO2 has Pb(+4) as O takes it's group oxidation state of O(-2)
Pb2+ is, clearly, Pb(+2)
So Pb takes two electrons when reacting. Hence; the first step is
2e- + PbO2 -->Pb2+
Now, you need to balance the elements. Two O's on the left need to appear on the right. Oxygen will keep its formal oxidation state, so there is no electron transfer occurring there.
2e- + PbO2 --> Pb2+ + 2O2- (bear in mind that this is not a real process)
Now, you need to couple the O2- with hydrogen ions to make water.
2e- + 4H+ + PbO2 --> Pb2+ + 2H2O
So, now you have equalised charges, elements, and no unphysical ions like O2-
So [A] is done.

[b]

Cl- --> Cl2
First, as it's unimolecular, balance the number of atoms.
2Cl- --> Cl2
Now look at oxidation state.
Left Cl(-1) goes to right Cl(0) (as it is the elemental form).
So you need to balance the electrons now.
2Cl- --> Cl2 + 2e-

Now it's time to combine [A] and [B]

The electrons need to cancel is the magic rule, remember.

2e- + 4H+ + PbO2 --> Pb2+ + 2H2O
2Cl- --> Cl2 + 2e-

As there are two on each side, you can literally just add the sides together.

Hence; finally-

2Cl- +4H++PbO2 --> Pb2+ + Cl2 + 2H2O

Can you name the oxidised species? The reduced species?

Which is the oxidising agent?

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Updated: September 13, 2015
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