Oxidation and Reduction as a Process Any chemical process in which elements undergo changes in oxidation number is an oxidation-reduction reaction. This name is often shortened toredox reaction. The part of the reaction involving oxidation or reduction alone can be written as a half-reaction. Section 1 Oxidation and Reduction Chapter 19

Equations for the reaction between nitric acid and copper illustrate the relationship between half-reactions and the overall redox reaction. Section 1 Oxidation and Reduction Chapter 19 Oxidation and Reduction as a Process, continued (oxidation half-reaction) (reduction half-reaction) (redox reaction)

Oxidation and Reduction as a Process, continuedRedox Reactions and Covalent Bonds When hydrogen burns in chlorine, a covalent bond forms from the sharing of two electrons. The pair of electrons is more strongly attracted to the chlorine atom because of its higher electronegativity. Section 1 Oxidation and Reduction Chapter 19

Oxidation and Reduction as a Process, continuedRedox Reactions and Covalent Bonds, continued Neither atom has totally lost or totally gained any electrons. Hydrogen has donated a share of its bonding electron to the chlorine but has not completely transferred that electron. Section 1 Oxidation and Reduction Chapter 19

Section 1 Oxidation and Reduction Chapter 19 Particle Model for a Redox Reaction

Visual Concepts Chapter 19 Half-Reaction Equation

Objectives Explain what must be conserved in redox equations. Balance redox equations by using the half-reaction method. Section 2 Balancing Redox Equations Chapter 19

Half-Reaction Method The half-reaction method for balancing redox equations consists of seven steps: 1. Write the formula equation if it is not given in the problem. Then write the ionic equation. 2. Assign oxidation numbers. Delete substances containing only elements that do not change oxidation state. Section 2 Balancing Redox Equations Chapter 19

Half-Reaction Method, continued 3. Write the half-reaction for oxidation. Balance the atoms. Balance the charge. 4. Write the half-reaction for reduction. Balance the atoms. Balance the charge. Section 2 Balancing Redox Equations Chapter 19

Half-Reaction Method, continued 5. Conserve charge by adjusting the coefficients in front of the electrons so that the number lost in oxidation equals the number gained in reduction. 6. Combine the half-reactions, and cancel out anything common to both sides of the equation. 7. Combine ions to form the compounds shown in the original formula equation. Check to ensure that all other ions balance. Section 2 Balancing Redox Equations Chapter 19

Section 2 Balancing Redox Equations Chapter 19 Balancing Redox Equations Using the Half-Reaction Method

Visual Concepts Chapter 19 Rules for the Half-Reaction Method

Half-Reaction Method, continued Sample Problem A A deep purple solution of potassium permanganate is titrated with a colorless solution of iron(II) sulfate and sulfuric acid. The products are iron(III) sulfate, manganese(II) sulfate, potassium sulfate, and water—all of which are colorless. Write a balanced equation for this reaction. Section 2 Balancing Redox Equations Chapter 19

Half-Reaction Method, continued Sample Problem A Solution 1. Write the formula equation if it is not given in the problem. Then write the ionic equation. Section 2 Balancing Redox Equations Chapter 19

Sample Problem A Solution, continued 2. Assign oxidation numbers to each element and ion. Delete substances containing an element that does not change oxidation state. Section 2 Balancing Redox Equations Chapter 19 Half-Reaction Method, continued Only ions or molecules whose oxidation numbers change are retained.

Sample Problem A Solution, continued 3. Write the half-reaction for oxidation. The iron shows the increase in oxidation number. Therefore, it is oxidized. Balance the mass. The mass is already balanced. Balance the charge. Section 2 Balancing Redox Equations Chapter 19 Half-Reaction Method, continued

Half-Reaction Method, continued Sample Problem A Solution, continued 4. Write the half-reaction for reduction. Manganese is reduced. Section 2 Balancing Redox Equations Chapter 19 • Balance the mass. • Water and hydrogen ions must be added to balance the oxygen atoms in the permanganate ion. Balance the charge.

Half-Reaction Method, continued Sample Problem A Solution, continued 5. Adjust the coefficients to conserve charge. Section 2 Balancing Redox Equations Chapter 19

Sample Problem A Solution, continued 6. Combine the half-reactions and cancel. Section 2 Balancing Redox Equations Chapter 19 Half-Reaction Method, continued

Sample Problem A Solution, continued 7. Combine ions to form compounds from the original equation. Section 2 Balancing Redox Equations Chapter 19 Half-Reaction Method, continued

Lesson Starter Label a small object (such as an empty box) “electrons.” Ask another student to take the electrons from you. The other student was the agent of your losing the electrons and you were the agent of the other student’s gaining the electrons. Section 3 Oxidizing and Reducing Agents Chapter 19

Lesson Starter, continued By causing you to lose your electrons, the other student is the oxidizing agent. You are the reducing agent because you caused the student to gain electrons. The student is reduced by you, and you are oxidized by the other student. Section 3 Oxidizing and Reducing Agents Chapter 19

Objectives Relate chemical activity to oxidizing and reducing strength. Explain the concept of disproportionation. Section 3 Oxidizing and Reducing Agents Chapter 19

Areducing agentis a substance that has the potential to cause another substance to be reduced. An oxidizing agentis a substance that has the potential to cause another substance to be oxidized. Section 3 Oxidizing and Reducing Agents Chapter 19

Strengths of Oxidizing and Reducing Agents, continued Section 3 Oxidizing and Reducing Agents Chapter 19

Strengths of Oxidizing and Reducing Agents, continued Different substances can be compared and rated by their relative potential as reducing and oxidizing agents. The negative ion of a strong oxidizing agent is a weak reducing agent. The positive ion of a strong reducing agent is a weak oxidizing agent. Section 3 Oxidizing and Reducing Agents Chapter 19

Disproportionation A process in which a substance acts as both an oxidizing agent and a reducing agent is called disproportionation. A substance that undergoes disproportionation is bothself-oxidizingandself-reducing. example: Hydrogen peroxide is both oxidized and reduced Section 3 Oxidizing and Reducing Agents Chapter 19

End of Chapter 19 Show

Multiple Choice 1. In the following reaction, which species is reduced? A. K B. Br2 C. All of the above D. None of the above Standardized Test Preparation Chapter 19

1. In the following reaction, which species is reduced? A. K B. Br2 C. All of the above D. None of the above Standardized Test Preparation Chapter 19 Multiple Choice

2. The oxidation number of the sulfur atom in the A. +2. B. −2. C. +6. D. +4. Standardized Test Preparation Chapter 19 Multiple Choice

2. The oxidation number of the sulfur atom in the A.+2. B. −2. C. +6. D. +4. Standardized Test Preparation Chapter 19 Multiple Choice

3. A half-reaction A. involves a change in the oxidation state of an element. B. always contains H2O molecules. C.always contains H+ ions. D. All of the above Standardized Test Preparation Chapter 19 Multiple Choice

3. A half-reaction A. involves a change in the oxidation state of an element. B. always contains H2O molecules. C. always contains H+ ions. D. All of the above Standardized Test Preparation Chapter 19 Multiple Choice

4. In the following reaction, which is the oxidizing agent? A. AgNO2 B. Cl2 C. KOH D. KCl Standardized Test Preparation Chapter 19 Multiple Choice

5. What are the oxidation states (in increasing order) of the element that undergoes disproportionation in the following reaction: A. −1, 0, +2 B. −1, 0, +1 C. −2, −1, 0 D. None of the above Standardized Test Preparation Chapter 19 Multiple Choice

6. Which reaction is a redox reaction? A. B. C. D. Standardized Test Preparation Chapter 19 Multiple Choice

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