4.3 Oxidation-Reduction Reactions
What is an Oxidation-Reduction Reaction?
An oxidation-reduction reaction (a.k.a. redox reaction) is a reaction in which electrons are transferred from one species (oxidized) to another species (reduced). The evidence that a redox reaction has occurred are changes in oxidation states (charges).
Oxidation is the loss of electrons. (OIL) (LEO)
Reduction is the gain of electrons. (RIG) (GER)
Oxidation-Reduction Rules
| OXIDATION STATE RULES | |
|---|---|
| 1 | Atoms in their elemental form are in the zero oxidation state. |
| 2 | Monatomic ions in ionic compounds get their typical ionic charge. The oxidation states of transition metals are determined based upon the anion they are with. |
| 3 | Atoms in Molecular Compounds and Polyatomic Ions Hydrogen +1 (when bonded with any nonmetals) Oxygen -2 except in peroxide O22- Fluorine -1 always Halogens -1 except when bonded to Oxygen |
| 4 | The oxidation numbers sum to zero for a compound or to the overall charge of a polyatomic ion. |
Assign oxidation states to the elements in the following elements/compounds:
Na Cl2 O3
MgCl2 CuCl2 H2SO4
Identify the species that are oxidized and reduced in the following reaction:
Zn(s) + 2MnO2(s) → ZnO(s) + Mn2O3(s)
Single Replacement Reactions
If the species being oxidized in a single replacement reaction is higher on the activity series than the species being reduced, the reaction will be spontaneous.
Which of the two reactions below are spontaneous?
Cu(s) +Zn(NO3)2(aq) → Cu(NO3)2(aq) + Zn(s)
Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
