Redox Reactions 13.1a Electron Transfer Theory

Overview oxidation and reduction rxtns always occur together (redox rxtn) –you can’t have one without the other examples –extracting metal from an ore –electroplating of metals –salt on roads (corrosion) salt accelerates the reaction between oxygen and metal makes electron transfer easier

3 perspectives of oxidation/reduction 1) oxygen –oxidation gains and reduction loses 2) hydrogen –oxidation loses and reduction gains 3) electrons (modern view) –oxidation loses and reduction gains –most fundamental explanation, what we will be working with the most

Sample Rxtn. We convert iron ore to metallic iron using carbon. What is being oxidized? 2Fe 2 O 3 + 3C  4Fe + 3CO 2 –we removed oxygen from the iron(III)oxide and the carbon gained oxygen –carbon was oxidized because it gained an oxygen

Sample Rxtns. con’t Fe 2 O 3 (s) + 3 CO (g) 2 Fe (s) + 3CO 2 (g) SnO 2 (s) + C (s)  Sn (s) + CO 2 (g) CuS (s) + H 2(g)  Cu (s) + H 2 S (g)

OxidationReduction Gains oxygenLose Oxygen Lose HydrogenGains hydrogen Lose ElectronsGains electrons Oxygen Hydrogen e-e-

Redox with Electrons many reactions may not even involve oxygen redox currently refers to electrons being transferred between reactants Mg + S Mg 2+ + S 2- the magnesium atom (which has zero charge) changes to a magnesium ion by losing 2 electrons, and is oxidized to Mg 2+ the sulfur atom (which has no charge) is changed to a sulfide ion by gaining 2 electrons, and is reduced to S 2- Mg is the reducing agent and S is the oxidizing agent agents cause the other half of the rxtn. to occur (MgS)

Examples Is the reactant oxidized or reduced? Pb  PbO 3 oxidized SnO 2  SnOreduced KClO 3  KCl reduced C 2 H 6 O  C 2 H 4 O oxidized C 2 H 2  C 2 H 6 reduced

Homework Textbook p. 559 #1-4

Redox Reactions 13.1a 1 Electron Transfer Theory

Leo the Lion! LEO the lion says GER –Loss of electrons is oxidation, gain of electrons is reduction

LEO says GER LEO says GER Lose Electrons = Oxidation Sodium is oxidized Gain Electrons = Reduction Chlorine is reduced

LEO says GER con’t LEO says GER con’t - losing electrons is oxidation, and the substance that loses the electrons is called the reducing agent. - gaining electrons is reduction, and the substance that gains the electrons is called the oxidizing agent. Mg (s) + S (s) MgS (s) Mg is oxidized: loses e -, becomes a Mg 2+ ion S is reduced: gains e - = S 2- ion Mg is the reducing agent S is the oxidizing agent

Oxidizing and Reducing Agents CuO + H 2  Cu + H 2 O Cu goes from 2+ to 0 –Cu is reduced, therefore it is called an oxidizing agent because it causes some other substance to be oxidized H goes from 0 to 1+ –H is oxidized, therefore it is called a reducing agent because it causes some other substance to be reduced

Identifying Agents in an Equation CuO + H 2  Cu + H 2 O Reduction: CuO is the oxidizing agent Oxidation: H 2 is the reducing agent

A) H 2 (g) + Cl 2 (g) 2HCl(g) H 2 oxidized Cl 2 reduced B) S(s) + Cl 2 (g) SCl 2 (g) S oxidized Cl 2 reduced C) N 2 + 2O 2 2NO 2 N 2 oxidized O 2 reduced D) 2Li + F 2 2LiF Li oxidized F 2 reduced E) H 2 + S H 2 S H 2 oxidized S reduced Examples

Half-Cell Reactions The overall reaction: 2Fe + 3Cl 2 2Fe Cl - may be written as the sum of two half-cell reactions: 2Fe  2Fe e - (oxidation) 3Cl 2 + 6e -  6Cl - (reduction) Complete redox reactions can be expressed as the sum of two half reactions, one reduction and one oxidation.

Homework Textbook p.564 #7-11 LSM 13.1B,C summary