Oxidation and Reduction?

Question

Identify which reagent gets reduced in each of the following redox reactions.


Zn CuCl2 CuCl2 + Zn ZnCl2 + Cu


PtS O2 2PtS + 3O2 2PtO + 2SO2


Cr2O3 Si 3Si + 2Cr2O3 4Cr + 3SiO2


H2 N2 3H2 + N2 2NH3


?I though it was all the elements that are by themselves like Zn for th first one ad PtS for the second one but those answers are not working for me..Hlp please...

Answer 1

1. Cu2+ ions (or CuCl2)
2. O2
3. Cr3+ ions (or Cr2O3)
4. N2

You have to understand the concept of oxidation state (or oxidation number) and work out which element has gone down in value.