Section 18.1 Electron Transfer Reactions 1.To learn about metal-nonmetal oxidation–reduction reactions 2.To learn to assign oxidation states Objectives

Section 18.1 Electron Transfer Reactions A. Oxidation-Reduction Reactions Oxidation-reduction reaction – a chemical reaction involving the transfer of electrons –Oxidation – loss of electrons –Reduction – gain of electrons

Section 18.1 Electron Transfer Reactions A. Oxidation-Reduction Reactions –Which element is oxidized? –Which element is reduced?

Section 18.1 Electron Transfer Reactions B. Oxidation States Oxidation states – allow us to keep track of electrons in oxidation-reduction reactions

Section 18.1 Electron Transfer Reactions B. Oxidation States

Section 18.2 Balancing Oxidation-Reduction Reactions 1.To understand oxidation and reduction in terms of oxidation states 2.To learn to identify oxidizing and reducing agents 3.To learn to balance oxidation-reduction equations using half reactions Objectives

Section 18.2 Balancing Oxidation-Reduction Reactions A. Oxidation-Reduction Reactions Between Nonmetals Na  oxidized –Na is also called the reducing agent (electron donor). Cl 2  reduced –Cl 2 is also called the oxidizing agent (electron acceptor). 2Na(s) + Cl 2 (g)  2NaCl(s)

Section 18.2 Balancing Oxidation-Reduction Reactions A. Oxidation-Reduction Reactions Between Nonmetals C  oxidized –CH 4 is the reducing agent. O 2  reduced –O 2 is the oxidizing agent. CH 4 (g) + 2O 2 (g)  CO 2 (g) + 2H 2 O(g)

Section 18.2 Balancing Oxidation-Reduction Reactions B. Balancing Oxidation-Reduction Reactions by the Half-Reaction Method Half reaction – equation which has electrons as products or reactants

Section 18.2 Balancing Oxidation-Reduction Reactions B. Balancing Oxidation-Reduction Reactions by the Half-Reaction Method

Section 18.3 Electrochemistry and Its Applications 1.To understand the concept of electrochemistry 2.To learn to identify the components of an electrochemical (galvanic) cell 3.To learn about commonly used batteries 4.To understand corrosion and ways of preventing it 5.To understand electrolysis 6.To learn about the commercial preparation of aluminum Objectives

Section 18.3 Electrochemistry and Its Applications A. Electrochemistry: An Introduction Electrochemistry – the study of the interchange of chemical and electrical energy Two types of processes –Production of an electric current from a chemical reaction –The use of electric current to produce chemical change

Section 18.3 Electrochemistry and Its Applications A. Electrochemistry: An Introduction Making an electrochemical cell

Section 18.3 Electrochemistry and Its Applications A. Electrochemistry: An Introduction If electrons flow through the wire charge builds up. Solutions must be connected to permit ions to flow to balance the charge.

Section 18.3 Electrochemistry and Its Applications A. Electrochemistry: An Introduction A salt bridge or porous disk connects the half cells and allows ions to flow, completing the circuit.

Section 18.3 Electrochemistry and Its Applications A. Electrochemistry: An Introduction Electrochemical battery (galvanic cell) – device powered by an oxidation-reduction reaction where chemical energy is converted to electrical energy Anode – electrode where oxidation occurs Cathode – electrode where reduction occurs

Section 18.3 Electrochemistry and Its Applications A. Electrochemistry: An Introduction Electrolysis – process where electrical energy is used to produce a chemical change –Nonspontaneous

Section 18.3 Electrochemistry and Its Applications B. Batteries Lead Storage Battery –Anode reaction - oxidation Pb + H 2 SO 4  PbSO 4 + 2H + + 2e  –Cathode reaction - reduction PbO 2 + H 2 SO 4 + 2e  + 2H +  PbSO 4 + 2H 2 O

Section 18.3 Electrochemistry and Its Applications B. Batteries –Overall reaction Pb + PbO 2 + 2H 2 SO 4  2PbSO 4 + 2H 2 O

Section 18.3 Electrochemistry and Its Applications B. Batteries Electric Potential – the “pressure” on electrons to flow from anode to cathode in a battery

Section 18.3 Electrochemistry and Its Applications B. Batteries Dry Cell Batteries – do not contain a liquid electrolyte –Acid version Anode reaction - oxidation Zn  Zn e  Cathode reaction – reduction 2NH MnO 2 + 2e   Mn 2 O 3 + 2NH 3 + 2H 2 O

Section 18.3 Electrochemistry and Its Applications B. Batteries Dry Cell Batteries – do not contain a liquid electrolyte –Alkaline version Anode reaction - oxidation Zn + 2OH   ZnO + H 2 O + 2e  Cathode reaction – reduction 2MnO 2 + H 2 O + 2e   Mn 2 O 3 + 2OH 

Section 18.3 Electrochemistry and Its Applications B. Batteries Dry Cell Batteries – do not contain a liquid electrolyte –Other types Nickel-cadmium – rechargeable Silver cell – Zn anode, Ag 2 O cathode Mercury cell – Zn anode, HgO cathode

Section 18.3 Electrochemistry and Its Applications C. Corrosion Corrosion is the oxidation of metals to form mainly oxides and sulfides. –Some metals, such as aluminum, protect themselves with their oxide coating. –Corrosion of iron can be prevented by coatings, by alloying and cathodic protection. Cathodic protection of an underground pipe

Section 18.3 Electrochemistry and Its Applications D. Electrolysis Electrolysis – a process involving forcing a current through a cell to produce a chemical change that would not otherwise occur