I'm supposed to balance a redox reaction that occurs in an acidic solution.
I already balanced it(h**p://img148.imageshack.us/img148/4304/redoxht8.jpg), but how do I tell if a half-reaction is oxidation or reduction? I know an oxidation reaction loses electrons, and an reduction reaction gains electrons, but how do I tell from the reaction?
If electrons are added to the left side of the half reaction, it is a reduction. In the reaction you are referring to, ClO3- is reduced and As2S3 is oxidized.
I see. TY.
To determine if a half-reaction is oxidation or reduction, you can follow these steps:
1. Identify the changes in oxidation numbers: Start by identifying the oxidation numbers of the atoms involved in the half-reaction. The oxidation number is the charge that an atom would have if the electron pairs in a compound were divided equally.
2. Compare the oxidation numbers before and after: Compare the oxidation numbers of each atom before and after the reaction. If the oxidation number of an atom increases, it is undergoing oxidation because it is losing electrons. Conversely, if the oxidation number of an atom decreases, it is undergoing reduction because it is gaining electrons.
Looking at the balanced redox reaction you provided:
MnO4- + 8H+ + 5e- → Mn2+ + 4H2O
Fe2+ → Fe3+ + e-
In the first half-reaction, the oxidation number of Mn increases from +7 to +2. This means that Mn is undergoing reduction, gaining electrons and getting reduced from MnO4- to Mn2+.
In the second half-reaction, the oxidation number of Fe increases from +2 to +3. Therefore, Fe is undergoing oxidation, losing electrons and getting oxidized from Fe2+ to Fe3+.
Remember, oxidation is the loss of electrons, and reduction is the gain of electrons.