Oxidizing and Reducing Agents and Spontaneity

1. Oxidizing and Reducing Agents and Spontaneity Section 13.2 Freiman

2. Oxidizing and Reducing Agents • A REDUCING AGENT reduces another substance by giving it electrons in a reaction • Because they lose electrons, RAs are OXIDIZED • An OXIDIZING AGENT oxidizes another substance by taking electrons from it in a reaction • Because they gain electrons, OAs are REDUCED

3. Table of REDOX half-reactions • This table is on pg. 828 • Organized by strength of OAs an RAs • Strong Oxidizing Agents (SOA) are top left • Strong Reducing Agents (SRA) are bottom right

4. Spontaneity • Not all substances will react together in a redox reaction. There is a simple rule to predict spontaneity of redox reactions: • If left side (SOA) HIGHER than right side (SRA), reaction is spontaneous and products will form

5. Examples • If copper(II) sulfate and zinc metal were placed in a beaker, would a spontaneous reaction occur? • If nickel oxide and lead metal were placed in a beaker, would a spontaneous reaction occur?

7. Homework • Read Section 13.2 – Pgs. 568-569 • Worksheet – Oxidation and Reduction Review

8. Building Redox Tables Chapter 13.2 Freiman

9. The Reduction table in the data book does not contain every single OA or RA that exists. • Reduction tables can be made from data obtained in the lab. • By reacting various elements in single replacement reactions, OAs and RAs can be ranked according to strength. • Remembering the spontaneity rule

10. SOA SRA

11. Example • Using each of the following reactions, write the reduction table for tungsten, rhodium and osmium • Os4+(aq) + Rh(s) Os(s) + Rh3+(aq) • W(s) + Os4+(aq)  W6+(aq) + Os(s) • W(s) + Rh3+(aq)  no reaction

12. Steps • For the 1st reaction, determine the OA and the RA. • If reaction is spontaneous, then OA is higher than RA on the chart. • If NOT spontaneous, then RA is higher than OA on the chart • Repeat step one for all other reactions • Once the relative strength of all OAs and RAs have been determined, write the REDUCTION HALF REACTIONS in order of strength. (Indicate SOA and SRA in the corners)

14. Example 2 • Write a reduction half-reaction table using the information from the following lab results. • LaCl3(aq) + V(s) no reaction • LaCl3(aq) + Ga(s)  products form • Y(s) + VBr5(aq)  no reaction • GaCl3(aq) + Sc(s)  products form

16. Predicting Redox Reactions Section 13.2 Freiman

17. Predicting Redox Reactions • When performing a reaction in a solution, there may be more than one oxidizing agent or reducing agent. • Predicting redox reactions requires a 5-step process

18. Steps • List all entities in solution and classify them as oxidizing or reducing agents OR BOTH • Choose SOA and SRA • Write the half-reactions • Balance and write the full redox reaction • Predict spontaneity (spontaneous or not spontaneous)

19. Hints • Aqueous solution means H2O(l) is present • Acidic solution means H+ is present • Basic solution means OH- is present • Some oxidizing and reducing agents are COMBINATIONS – find the combinations! • Watch for DISPROPORTIONATIONS – reduction and oxidation happen to the SAME ENTITY

20. Examples 1. What is the redox reaction that occurs when copper metal is placed in an acidic potassium permanganate solution??? 2. Can an iron container be used to transport a mixture of hydrochloric acid and zinc bromide?