Electrochemistry Oxidation Numbers Redox Reactions Oxidizing & Reducing Agents

Oxidation States Oxidation state of an element is 0. Oxidation state of a monatomic ion is the same as its charge. Oxidation state of F is –1. Oxidation state of O is usually –2. –In peroxides, H 2 O 2, oxygen is -1 –In OF 2 oxygen is +2

Oxidation States Oxidation state of H is usually +1. –H combined with a metal from columns 1, 2, or 3 has an oxidation state of -1 Sum of oxidation states should equal charge on an ion or “0” for a compound.

A Problem For You Identify the oxidation states of all atoms in the following molecules. MgSO 4 Na 2 C 2 O 4 H2O2H2O2 Cr 2 O 3

Another Problem For You Identify the oxidation states of all atoms in the following ions. SO 3 -2 PO 4 -3 AsO 4 -3 IO -

Electrons are transferred from the reducing agent to the oxidizing agent Reduction involves gaining e- Oxidation involves losing e- Easiest to look at each half-reaction Oxidation & Reduction

Oxidation and Reduction  A reaction in which electrons are involved  Electrons are given up or taken on during this type of reaction  Both electrons and atoms must balance in this type of reaction

Oxidation and Reduction  Reactions that involve a loss or gain of electrons  Occurs in many of the 4 types of reactions and combustion  Important in food metabolism, batteries, rusting of metals

Electrons are transferred Two processes occur Oxidation = Loss of electrons (LEO) Zn  Zn e - Reduction = Gain of electrons (GER) Cu e -  Cu Requirements for Oxidation and Reduction

Balanced Red-Ox Equations Combine the oxidation and reduction reactions to make Loss of electrons = Gain of electrons Zn + Cu e -  Zn e - + Cu Zn + Cu 2+  Zn 2+ + Cu

Gain/Loss of Hydrogen In organic and biological reactions oxidation = Loss of H reduction = Gain of H

Identifying Oxidation & Reduction Identify the following as an 1) oxidation or a 2) reduction process: __A. Sn  Sn e- __B. Fe e -  Fe 2+ __C. Cl 2 + 2e -  2Cl -

Solution Identify the following as an 1) oxidation or a 2) reduction process: 1_ A. Sn Sn e- 2_ B. Fe e - Fe 2+ 2_ C. Cl 2 + 2e - 2Cl -

Idendtifying Oxidation & Reduction In light-sensitive sunglasses, UV light initiates an oxidation-reduction reaction Ag + + Cl - Ag + Cl A. Which reactant is oxidized 1) Ag + 2) Cl - 3) Ag B. Which reactant is reduced? 1) Ag + 2) Cl - 3) Cl

Solution In light-sensitive sunglasses, UV light initiates an oxidation-reduction reaction Ag + + Cl - Ag + Cl A. Which reactant is oxidized 2) Cl - Cl - Cl + e - B. Which reactant is reduced? 1) Ag + Ag + + e- Ag

Oxidizing and Reducing Agents *An oxidizing agent is the substance being reduced * A reducing agent is the substance being oxidized

Select the Oxidizing and Reducing Agents in this reaction In light-sensitive sunglasses, UV light initiates an oxidation-reduction reaction Ag + + Cl - Ag + Cl A. Which reactant is the oxidizing agent? 1) Ag + 2) Cl - 3) Ag B. Which reactant is the reducing agent? 1) Ag + 2) Cl - 3) Cl

Solution In light-sensitive sunglasses, UV light initiates an oxidation-reduction reaction Ag + + Cl - Ag + Cl A. Which reactant is the oxidizing agent? 1) Ag + B. Which reactant is the reducing agent? 2) Cl -

Redox Reactions Identify the oxidizing agent, the reducing agent, the substance being oxidized, and the substance being reduced. __Ag + + __ Al (s)  __ Ag (s) + __ Al 3+ ___I - + ___Cl 2(g)  ___I 2(s) + ___ Cl - ___CS 2 + __ O 2(s)  __ CO 2 + __ SO 2

Redox Reactions-Solution Identify the oxidizing agent, the reducing agent, the substance being oxidized, and the substance being reduced. 3 Ag + + __ Al (s)  3 Ag (s) + __ Al 3+ –Silver ion is the oxidizing agent (reduced) –Aluminum is the reducing agent (oxidized) I - + ___Cl 2(g)  ___I 2(s) + 2 Cl - 2 ____ –Iodide ion is the reducing agent (oxidized) –Chlorine is the oxidizing agent (reduced) ___CS O 2(s)  __ CO SO 2 –Carbon disulfide is the reducing agent (oxidized) –Oxygen is the oxidizing agent (reduced)