00:01
Okay, so for the first reaction, the highlighted atom, the oxygen, is it being oxidized or reduced? well, in order to determine that, we want to determine the oxidation numbers.
00:11
So on the left -hand side, oxygen exists as a free element in its standard state, so its oxidation number is zero.
00:17
In the second situation here on the right -hand side, it's part of a compound, and oxygen, unless it's bonded to fluorine -orientic peroxide, is going to have an oxidation number of minus two.
00:28
So the oxidation number decreases, meaning that it's reduction.
00:32
And the oxidation number goes down, an element is reduced.
00:36
Okay.
00:37
Next, we are dealing with copper.
00:39
So in this case, copper is part of a compound.
00:42
Oxidation number is going to be equal to its charge.
00:44
Sulfate always has a charge of minus two, so the copper here is copper 2 plus.
00:49
And here, in the free element state, it's zero.
00:52
So its oxidation number has gone down, so we say that copper is reduced.
00:58
All right.
00:59
For the third one, here chromium is part of chromate...