Oxidation-Reduction Reactions: Understanding Redox and Balancing Equations

CHAPTER 20 “ Oxidation-Reduction Reactions” LEO SAYS GER

Section 20.1 The Meaning of Oxidation and Reduction (called “redox”) ,[object Object],[object Object]

Section 20.1 The Meaning of Oxidation and Reduction (Redox) ,[object Object],[object Object]

Oxidation and Reduction (Redox) ,[object Object],[object Object]

Oxidation and Reduction (Redox) ,[object Object],[object Object],[object Object],[object Object]

Oxidation and Reduction (Redox) ,[object Object],[object Object],[object Object]

Oxidation and Reduction (Redox) ,[object Object],[object Object],[object Object],[object Object],[object Object],(MgS)

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

LEO says GER : L ose E lectrons = O xidation Sodium is oxidized G ain E lectrons = R eduction Chlorine is reduced

LEO says GER : - Losing electrons is oxidation, and the substance that loses the electrons is called the reducing agent . - Gaining electrons is reduction, and the substance that gains the electrons is called the oxidizing agent . Mg (s) + S (s) -> MgS (s) Mg is oxidized : loses e - , becomes a Mg 2+ ion S is reduced : gains e - = S 2- ion Mg is the reducing agent S is the oxidizing agent

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

Corrosion ,[object Object],[object Object],[object Object]

Corrosion ,[object Object],[object Object],[object Object],[object Object]

Corrosion ,[object Object],[object Object],[object Object],[object Object],[object Object]

Section 20.2 Oxidation Numbers ,[object Object],[object Object]

Assigning Oxidation Numbers ,[object Object],[object Object]

Rules for Assigning Oxidation Numbers ,[object Object],[object Object]

Rules for Assigning Oxidation Numbers ,[object Object],2(+1) + (-2) = 0 H O (+2) + 2(-2) + 2(+1) = 0 Ca O H

Rules for Assigning Oxidation Numbers ,[object Object],X + 3(-2) = -1 N O thus X = +5 thus X = +6 X + 4(-2) = -2 S O

Reducing Agents and Oxidizing Agents ,[object Object],[object Object],[object Object],Sodium is oxidized – it is the reducing agent Chlorine is reduced – it is the oxidizing agent

Trends in Oxidation and Reduction ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Conceptual Problem 20.3, page 643

Section 20.3 Balancing Redox Equations ,[object Object],[object Object]

Identifying Redox Equations ,[object Object],[object Object],[object Object],[object Object],[object Object]

Identifying Redox Equations ,[object Object],[object Object],[object Object],[object Object],[object Object],YES!

Balancing Redox Equations ,[object Object],[object Object],[object Object],[object Object]

Using Oxidation-Number Changes ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Using half-reactions ,[object Object],[object Object],[object Object],[object Object],[object Object],(More steps on the next screen.)

Choosing a Balancing Method ,[object Object],[object Object]

Using half-reactions ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Electrochemical (Voltaic) Cells ,[object Object],[object Object]

[object Object],[object Object]

Basic Concepts of Electrochemical Cells

Cathode ,[object Object],[object Object]

Anode ,[object Object],[object Object],[object Object]

Electrolytic Cells ,[object Object],[object Object],[object Object],[object Object]

Basic Concepts of Electrolytic Cells

Electrodes ,[object Object],[object Object]

Electrodes ,[object Object],[object Object],[object Object]

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Oxidation-Reduction Reactions: Understanding Redox and Balancing Equations