Redox Reactions What is oxidation? What is reduction?

What is REDOX? chemical reactions in which atoms have their oxidation state changed chemical reactions oxidation state family of reactions that are concerned with the transfer of electrons between species Rusting is an example of a redox reaction.

REDOX term comes from the two concepts of reduction and oxidation Oxidation is the loss of electrons or an increase in oxidation state Reduction is the gain of electrons or a decrease in oxidation state Oxidation State = the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic

Assigning Oxidation Numbers #1. All free, uncombined elements have oxidation number of 0. Includes diatomic elements such as O 2 #2. All monoatomic ions have the same oxidation # as the charge on the ion. Mg = +2Cl = -1 #3. All combined Hydrogen has oxidation # = +1. (except hydrides)

Assigning Oxidation Numbers #4. All combined Oxygen has oxidation # = -2. (except peroxides) #5. Polyatomics = sum of oxidation numbers of elements in ion equals the charge on that species Ex. Sulfate SO 4 2 ¯ O = -2. There are four oxygens for -8 total. Since -2 is left over, the S must = +6. #6. Group I = +1Group II = +2

EXAMPLES H 2 SO 4 H =O =S = MoO 4 -2 Mo = O =

Determining REDOX Species

4 Fe  2 Fe e- Was an electron gained or lost? An electron was produced or lost by Fe. LEO.. Losing electrons is oxidation. Fe was oxidized.

1 e- + 3 O 2  2 O 3 Was an electron gained or lost? An electron was gained by O 2. GER.. Gaining electrons is reduction. Oxygen was reduced.

Oxidation and Reduction ALWAYS occur together. One cannot occur without the other.

How does this occur? By oxidizing and reducing agents Oxidizing Agent = substance that removes an electron from another species – Ex. oxygen Reducing Agent = substance that donates an electron to another species – Ex. Iron, metals Full Rxn:4Fe + 3O 2 → 2Fe 2 O 3 Half Rxn: Fe 0 → Fe e − Half Rxn: O 2 + 4e − → 2 O 2− Iron is the reducing agent Oxygen is the oxidizing agent

Iron (Fe) has been oxidized because the oxidation number increased. (0  +3) Iron (Fe) is the reducing agent because it gave electrons to the oxygen (O 2 ). Oxygen (O 2 ) has been reduced because the oxidation number has decreased. (0  -2) Oxygen (O 2 ) is the oxidizing agent because it took electrons from iron (Fe). Full Rxn:4Fe + 3O 2 → 2Fe 2 O 3 Half Rxn: Fe 0 → Fe e − Half Rxn: O 2 + 4e − → 2 O 2−

Cl 2 (g) + 2NaBr (aq)  2NaCl (aq) + Br 2 (g) 1. Assign Oxidation Numbers O O Is it REDOX? Did oxidation numbers change? 3. LEO goes GER Who is oxidized? Who is reduced? Who is the oxidizing agent? Who is the reducing agent? Bromine Chlorine

Example