Oxidation and Reducing Agents?

Question

In 4H+(aq) + Pb(s) + PbO2(s) + 2SO42-(aq) -> 2PbSO4 + 2H2O(l), what is the oxidizing agent, and what is the reducing agent?

and in 6H2O(l) + 3S2-(aq) + 2CrO42-(aq) -> 2CrO2-(aq) + 3S(s) + 8OH- what is the oxidizing and reducing agent?

Please explain, don't just answer. Thank you.

Answer 1

It is simple but can be confusing, so here are two rules each in two parts (follow them and that's it):

a1) The oxidizing agent is the reactant containing the atom reduced
a2) The atom reduced is the atom whose oxidation number decreases

b1) The reducing agent is the reactant containing the atom oxidized
b2) The atom oxidized is the atom whose oxidation number increases

With these rules you can do everything yourself.

Dr.J.

Answer 2

Redox reactions involve the change in charge from reactants to products. To figure this out, you need to assign oxidation numbers. All single elements(elements by themselves) have an oxidation number of zero. All ions have oxidation numbers equal to their charge. H usually has a +1 oxidation number (in a compound) and oxygen usually has a -2 oxidation number(again, in a compound).

Use that to help you.