Redox Reactions

Oxidation Reduction (REDOX) Reactions Reactions in which one or more electrons are transferred (redox reactions) Example: H2(g) + Cl2(g) 2HCl(g) Electrons are transferred from the hydrogen to the chlorine. Recall Rules for Assigning Oxidation States Remember: The sum of the oxidation states in a neutral compound must equal zero.

Oxidation States Assign oxidation states to each of the atoms in the following compounds: Hint: Check that oxidation states sum up to the charge on the compound/ion. CaF2 C2H6 H2O ICl5 KMnO4 SO42-

Practice- Oxidation States Fe2O3 + 2Al Al2O3 + 2Fe THE IRON GAINED ELECTRONS. IT HAS BEEN REDUCED. THE ALUMINUM LOST ELECTRONS. IT HAS BEEN OXIDIZED. OIL – Oxidation Involves Loss (of electrons) RIG- Reduction Involves Gain (of electrons)

OIL RIG Practice For each reaction, identify the atoms that undergo reduction or oxidation (and charges). Also, list the oxidizing and reducing agents. 2H2(g) + O2(g) 2H2O(g) Zn(s) + Cu2+(aq) Zn2+(aq) + Cu(s) 2AgCl(s) + H2(g) 2H+(aq) + 2Ag(s) + 2Cl-(aq)

Tricky…Tricky… Fe2O3 + 2Al Al2O3 + 2Fe Oxidizing agent Reducing agent Something that is reduced (it causes something else to oxidize) Reducing agent Something that is oxidized (it causes something else to reduce) Fe2O3 + 2Al Al2O3 + 2Fe Iron was reduced. Aluminum was oxidized. Iron (II) oxide was the oxidizing agent. Aluminum was the reducing agent.

OIL RIG Practice For each reaction, identify the atoms that undergo reduction or oxidation (and charges). Also, list the oxidizing and reducing agents. 2H2(g) + O2(g) 2H2O(g) Zn(s) + Cu2+(aq) Zn2+(aq) + Cu(s) 2AgCl(s) + H2(g) 2H+(aq) + 2Ag(s) + 2Cl-(aq)

Balancing Oxidation-Reduction Equations (Half-Reaction Method) Steps: Acidic 1. Write separate equations for the oxidation and reduction half- reactions. 2. For each half-reaction Balance all the elements except hydrogen and oxygen. Balance oxygen using H2O. Balance hydrogen using H+. Balance the charge using electrons (e-). 3. If necessary, multiply one or both balanced half-reactions by an integer equalize the number of electrons transferred in the two half-reactions. 4. Add the half-reactions, and cancel identical species. 5. Check that the elements and charges are balanced.

Balancing Oxidation-Reduction Equations (Half-Reaction Method) Steps: Basic The same as acidic and then… 6. Add a number of OH- ions to both sides so that you just balance excess H+ ions. 7. H+ and OH- will form H2O on the side with excess H+. Free OH- will appear on one side of the equation. 8. Double check atoms and charges!

Balancing Redox Example - Acid Cu(s) + HNO3(aq) Cu2+(aq) + NO(g) Copper is being oxidized: Nitrogen is being reduced:

Balancing Redox Reactions - Base Cr2O72-(aq) + 2NO(g) + 6H+(aq) 2Cr3+(aq) + 2NO3-(aq) + 3H2O(l) **Already balanced in acid**