CHEM 121
Answers to Oxidation Number Part I Slide 9
a) SO42−
Assign -2 to oxygen, and S ends up with +6.
b) NH4+
Assign +1 to H and N ends up with −3
c) CoBr3
This is ionic so it forms monatomic ions: Co3+ and Br−
So, Co is +3 and Br is −1.
d) Fe(NO3)2
This is ionic so it forms Fe2+and NO3−. Fe is 2+.
YOU CANNOT GIVE AN OXIDATION FOR NITRATE AS SUCH.
Remember oxidation number is for EACH atom, not for the whole ion.
So, for nitrate (NO3−), assign −2 for O and N is +5.
NOTE ALSO THERE IS NO REASON TO DO (NO3)2. Just do one
nitrate (not two).
e) CrClO3
This is ionic, breaking up into Cr+ and ClO3−. Cr is +1 and from
ClO3−, you assign O as −2 and Cl becomes +5.
f) V2(OH)3
V has a variable charge so you have to figure that out from the anion,
OH−. Three OH− give a total charge of −3 So V2 would be a total of
+3, and EACH V would be +3/2.
From OH−, we assign +1 to H and O becomes −2.