Some harder redox half equation examples.

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About redox half equations.

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Oxidation States and Half Equations
(Done on the computer to help understand the changes better!)
The element which changes it's OXIDATION STATE is the one which is either losing or
gaining e¯`s
Example 1
I¯ I
2I¯ I + 2 e¯
Here the element only needs to lose two electrons, from the I¯ ions.
Example 2
Firstly, check the OXIDATION STATES of each element in the equation.
SO²¯ + 2e¯ SO
However we are still unbalanced!
We need to add some oxygen to our half equation, this comes in the form of HO, as this is
the source of oxygen in solution and in this equation needs to be added to the right-hand
SO²¯ + 2e¯ SO + 4HO
The addition of water means we need to balance out the addition of hydrogen using Hions.
4H + SO²¯ + 2e¯ SO + 4HO
Finally, make sure the charges on either side BALANCE.

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H + SO²¯ + 2e¯ SO + 4HO
From the equation we can see that both sides of the equation have an overall charge of 0.
Example 3
Sometimes compounds can carry different charges to expected, and also don't require all
three of HO and H.
Here we are going to balance the half equation of:
HO O + 2 e¯
The oxygens are already balanced therefore we only need to add H to the right-hand
side to balance the equation.…read more

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Now to consider the oxidation numbers of each of the elements, be careful!
2Cr³ CrO²¯
2Cr³ CrO…read more

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Cr³ CrO²¯ + 6e¯
As usual we need to balance our oxygens, this time adding them to the left-hand side.
7HO + 2Cr³ CrO²¯ + 6e¯
And then balance the H on the right-hand side, remember we need 14 H
7HO + 2Cr³ CrO²¯ + 6e¯ + 14H
Make sure the charges balance. Don't get numbers mixed up, remember that there
are 2xCr³, therefore on either side there needs to be a charge of +6 to balance.…read more


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