3- Oxidation-Reduction (Redox) titration Redox reaction: Define oxidation and reduction in terms of the loss or gain of oxygen, and the loss or gain of electrons. Redox reactions are characterized by ELECTRON TRANSFER between an electron donor and electron acceptor. A reversible chemical reaction in which one reaction is an oxidation and the reverse is a reduction

Terminology for Redox Reactions OXIDATION—loss of electron(s) by a species; increase in oxidation number; increase in oxygen. REDUCTION—gain of electron(s); decrease in oxidation number; decrease in oxygen; increase in hydrogen. OXIDIZING AGENT— electron acceptor; species is reduced. (an agent facilitates something; ex. Travel agents don’t travel, they facilitate travel) REDUCING AGENT—electron donor; species is oxidized. Valances— the electrical charge an atom would acquire if it formed ions in aqueous solution.

Oxidation and Reduction (Redox) Each sodium atom loses one electron: Each chlorine atom gains one electron:

Lose Electrons = Oxidation Sodium is oxidized Gain Electrons = Reduction Chlorine is reduced

Not All Reactions are Redox Reactions Reactions in which there has been no change in oxidation number are NOT redox reactions. Examples:

Electron Transfer Electron transfer reactions are oxidation-reduction or redox reactions. Results in the generation of an electric current (electricity) or be caused by imposing an electric current. Therefore, this field of chemistry is often called ELECTROCHEMISTRY.

Electrochemical processes are oxidation-reduction reactions in which: the energy released by a spontaneous reaction is converted to electricity (Galvanic cell) or electrical energy is used to cause a nonspontaneous reaction to occur (Electrolytic cell) 19.1

Therefore, we use a salt bridge, usually a U-shaped tube that contains a salt solution, to keep the charges balanced. Cations move toward the cathode. Anions move toward the anode. Salt Bridge allows current to flow H+ MnO4- Fe+2

CHEMICAL CHANGE ---> ELECTRIC CURRENT Electricity travels in a complete circuit e- H+ MnO4- Fe+2

- + Galvanic Cells anode oxidation cathode reduction spontaneous redox reaction 19.2

Line Notation solid /Aqueous//Aqueous/solid Anode on the left//Cathode on the right Single line different phases. Double line porous disk or salt bridge. If all the substances on one side are aqueous, a platinum electrode is indicated.

Standard Hydrogen Electrode Their values are referenced to a standard hydrogen electrode (SHE). By definition, the reduction potential for hydrogen is 0 V: 2 H+ (aq, 1M) + 2 e−  H2 (g, 1 atm)

Standard Cell Potentials The cell potential at standard conditions can be found through this equation:  Ecell = Ered (cathode) − Eoxid (anode) Because cell potential is based on the potential energy per unit of charge, it is an intensive property.

Cell Potentials Eox = −0.76 V  Ered = +0.34 V  For the oxidation in this cell, For the reduction, Eox = −0.76 V  Ered = +0.34 V 