Balancing oxidation-reduction equations, oxidation-reduction reactions, voltaic cells, cell EMF, effect of concentration on cell EMF is the main content of the lecture "Chapter 20: Electrochemistry". Invite you to consult the detailed content lectures to capture details. | Copyright 1999, PRENTICE HALL Chapter 20 Electrochemistry Chapter 20 David P. White University of North Carolina, Wilmington 1 1 1 1 Copyright 1999, PRENTICE HALL Chapter 20 Oxidation-Reduction Reactions Zn added to HCl yields the spontaneous reaction Zn(s) + 2H+(aq) Zn2+(aq) + H2(g). The oxidation number of Zn has increased from 0 to 2+. The oxidation number of H has reduced from 1+ to 0. Therefore, Zn is oxidized to Zn2+ while H+ is reduced to H2. H+ causes Zn to be oxidized and is the oxidizing agent. Zn causes H+ to be reduced and is the reducing agent. Note that the reducing agent is oxidized and the oxidizing agent is reduced. Copyright 1999, PRENTICE HALL Chapter 20 Balancing Oxidation-Reduction Equations Law of conservation of mass: the amount of each element present at the beginning of the reaction must be present at the end. Conservation of charge: electrons are not lost in a chemical reaction. In complicated redox reactions, we need to look at the transfer | Copyright 1999, PRENTICE HALL Chapter 20 Electrochemistry Chapter 20 David P. White University of North Carolina, Wilmington 1 1 1 1 Copyright 1999, PRENTICE HALL Chapter 20 Oxidation-Reduction Reactions Zn added to HCl yields the spontaneous reaction Zn(s) + 2H+(aq) Zn2+(aq) + H2(g). The oxidation number of Zn has increased from 0 to 2+. The oxidation number of H has reduced from 1+ to 0. Therefore, Zn is oxidized to Zn2+ while H+ is reduced to H2. H+ causes Zn to be oxidized and is the oxidizing agent. Zn causes H+ to be reduced and is the reducing agent. Note that the reducing agent is oxidized and the oxidizing agent is reduced. Copyright 1999, PRENTICE HALL Chapter 20 Balancing Oxidation-Reduction Equations Law of conservation of mass: the amount of each element present at the beginning of the reaction must be present at the end. Conservation of charge: electrons are not lost in a chemical reaction. In complicated redox reactions, we need to look at the transfer of electrons carefully. Half-Reactions Half-reactions are a convenient way of separating oxidation and reduction reactions. Copyright 1999, PRENTICE HALL Chapter 20 Balancing Oxidation-Reduction Equations Half-Reactions The half-reactions for Sn2+(aq) + 2Fe3+(aq) Sn4+(aq) + 2Fe3+(aq) are Sn2+(aq) Sn4+(aq) +2e- 2Fe3+(aq) + 2e- 2Fe2+(aq) Oxidation: electrons are products. Reduction: electrons are reagents. Copyright 1999, PRENTICE HALL Chapter 20 Balancing Oxidation-Reduction Equations Balancing Equations by the Method of Half-Reactions Consider the titration of an acidic solution of Na2C2O4 (sodium oxalate, colorless) with KMnO4 (deep purple). MnO4- is reduced to Mn2+ (pale pink) while the C2O42- is oxidized to CO2. The equivalence point is given by the presence of a pale pink color. If more KMnO4 is added, the solution turns purple due to the excess KMnO4. Copyright 1999, PRENTICE HALL Chapter 20 Balancing Oxidation-Reduction Equations Balancing Equations by the .
