1. Chapter 19 Preview Objectives Oxidation States Oxidation Reduction
Oxidation and Reduction as a Process

2. Section 1 Oxidation and Reduction
Chapter 19
Objectives
Assign oxidation numbers to reactant and product species.
Define oxidation and reduction.
Explain what an oxidation-reduction reaction (redox reaction) is.

3. Chapter 19 Oxidation States
Section 1 Oxidation and Reduction
Chapter 19
Oxidation States
The oxidation number assigned to an element in a molecule is based on the distribution of electrons in that molecule.
The rules by which oxidation numbers are assigned are summarized on the next slide.

4. Rules for Assigning Oxidation Numbers
Section 1 Oxidation and Reduction
Chapter 19
Rules for Assigning Oxidation Numbers

5. Assigning Oxidation Numbers
Section 1 Oxidation and Reduction
Chapter 19
Assigning Oxidation Numbers

6. Rules for Assigning Oxidation Numbers
Section 1 Oxidation and Reduction
Chapter 19
Rules for Assigning Oxidation Numbers
Click below to watch the Visual Concept.
Visual Concept

7. Section 1 Oxidation and Reduction
Chapter 19
Oxidation
Reactions in which the atoms or ions of an element experience an increase in oxidation state are oxidation processes.
A species whose oxidation number increases is oxidized.

8. Chapter 19 Oxidation Section 1 Oxidation and Reduction
Click below to watch the Visual Concept.
Visual Concept

9. Section 1 Oxidation and Reduction
Chapter 19
Reduction
Reactions in which the oxidation state of an element decreases are reduction processes.
A species that undergoes a decrease in oxidation state is reduced.

10. Chapter 19 Reduction Section 1 Oxidation and Reduction
Click below to watch the Visual Concept.
Visual Concept

11. Oxidation and Reduction as a Process
Section 1 Oxidation and Reduction
Chapter 19
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 to redox reaction.
The part of the reaction involving oxidation or reduction alone can be written as a half-reaction.

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

13. Section 1 Oxidation and Reduction
Chapter 19
Oxidation and Reduction as a Process, continued Redox 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.

14. Section 1 Oxidation and Reduction
Chapter 19
Oxidation and Reduction as a Process, continued Redox 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.

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

16. Half-Reaction Equation
Section 1 Oxidation and Reduction
Chapter 19
Half-Reaction Equation
Click below to watch the Visual Concept.
Visual Concept

17. Chapter 19 Preview Objectives Half-Reaction Method
Section 2 Balancing Redox Equations
Chapter 19
Preview
Objectives
Half-Reaction Method

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

19. Chapter 19 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.

20. Half-Reaction Method, continued
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.

21. Half-Reaction Method, continued
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.

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

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

24. Rules for the Half-Reaction Method
Section 2 Balancing Redox Equations
Chapter 19
Rules for the Half-Reaction Method
Click below to watch the Visual Concept.
Visual Concept

25. Half-Reaction Method, continued
Section 2 Balancing Redox Equations
Chapter 19
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.

26. Half-Reaction Method, continued
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.

27. Half-Reaction Method, continued
Section 2 Balancing Redox Equations
Chapter 19
Half-Reaction Method, continued
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.
Only ions or molecules whose oxidation numbers change are retained.

28. Half-Reaction Method, continued
Section 2 Balancing Redox Equations
Chapter 19
Half-Reaction Method, continued
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.

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

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

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

32. Half-Reaction Method, continued
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.

33. Chapter 19 Preview Lesson Starter Objectives
Section 3 Oxidizing and Reducing Agents
Chapter 19
Preview
Lesson Starter
Objectives
Strengths of Oxidizing and Reducing Agents
Disproportionation

34. Chapter 19 Lesson Starter
Section 3 Oxidizing and Reducing Agents
Chapter 19
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.

35. Lesson Starter, continued
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.

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

37. Section 3 Oxidizing and Reducing Agents
Chapter 19
A reducing agent is a substance that has the potential to cause another substance to be reduced.
An oxidizing agent is a substance that has the potential to cause another substance to be oxidized.

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

39. 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.

40. Chapter 19 Disproportionation
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 both self-oxidizing and self-reducing.
example: Hydrogen peroxide is both oxidized and reduced

41. End of Chapter 19 Show