class example

[805329408]

Just to clarify, in class Lavelle used the example:
8H+ + MnO4- + 5e- = Mn+2 + 4H2O where he said Mn is reduced from +7 to +2

Mn is initially +7 because O4 is is -8 and in order for the overall molecule to have a negative charge, Mn has to be +7 right? Thanks in advance!

[505316964]

That's correct. You know Mn has to be +7 in MnO4- because O4 has an overall -8 charge and the molecule has a -1 charge.

It is then being reduced to Mn 2+, as it's oxidation number decreases.

[Sidharth D 1E]

As a good rule of thumb, remember that oxygen in a compound other than O2 will have an oxidation number of -2 and hydrogen in a compound other than H2 will have an oxidation number of +1.