Redox Reactions

Part I: Define oxidation and reduction. Redox Notes Part I: Define oxidation and reduction.

Oxidation-Reduction Reactions Aka Redox Rxns Chemical reactions that transfer electrons from one chemical to another at the same time OXIDATION – the LOSS of electrons in a chemical rxn REDUCTION – the GAIN of electrons in a chemical rxn

Redox is a tandem process Oxidation cannot happen without reduction & vice versa Thus, you will have two types of agents (chemicals) OXIDIZING AGENT – substance that oxidizes another. It gets reduced. REDUCING AGENT - substance that reduces another. It gets oxidized.

Why can oxidation not happen without reduction? One substance that donates the electrons needs a place for the electrons to travel to. Electrons don’t just vanish; they attach to another atom. Therefore, one substance donates and the other accepts the electron.

Living Systems Photosynthesis and cellular respiration are biological examples of Redox reactions. Write the chemical equation for these reactions. Photosynthesis Cellular Respiration

Examples Photosynthesis Cellular Respiration 6CO2 + 6H2O  C6H12O6 + 6O2 Cellular Respiration 6O2 + C6H12O6  6CO2 + 6H2O

Non-Living Systems Fires, rusting, and metals reacting in acid are also examples of RedOx reactions

LEO goes GER Listen to him ROAR!!

Loss of Electrons = Oxidation Gain of Electrons = Reduction LEO the lion goes GER Loss of Electrons = Oxidation Gain of Electrons = Reduction

Think-Pair-Share Write your thoughts. When unbonded elements react to form compounds, one of the elements gains electrons (would that be the metal or the nonmetal?) while the other loses electrons (would that be the metal or the nonmetal?). Think about the formation of NaCl. Write your thoughts. Share your ideas with your partner. Share with the class.

REDOX Reaction Example Metals undergo Oxidation: loss of e- Ex Na  Na+ +e- Reduction: gain of e- Ex Cl2 + 2e- 2Cl- The Oxidizing Agent-substance reduced: Cl2 The Reducing Agent-substance oxidized: Na

Changes in oxidation number Oxidation number = number of e- gained or lost by an atom when it forms an ion EX: 2K + Br2  2KBr Potassium is oxidized from 0 to +1 Bromine is reduced from 0 to -1

Rules for Assigning Oxidation Numbers: 1. The oxidation # of an uncombined atom = 0. (ex: Na Al Br2 H2 etc) 2. The oxidation number of a monatomic ion is equal to the charge on the ion. (ex: Na1+ = +1, S2- = -2 etc) 3. H is always +1 (except when attached to more electronegative metals, Li, Na, Ca, and Al (ex: HCl H2SO4 NH3 etc) 4. O is always -2 (except in peroxides and when attached to F) (ex: H2O H2SO4 MgO)

Rules cont… 5. Group 1A, 2A, and 3A always have an oxidation number equal to the group number (equal to the charge it would have if it were a ion with noble gas configuration.) (ex: LiCl MgCl2 AlCl3) 6. If not neutral, sum of all oxidation numbers is equal to the overall charge on ion (ex: SO42- NH41+ HCO31-)

Exceptions Examples: O in CO2 is -2 O in LiOH is -2 O in Na3PO4 is -2 Oxygen that is bonded to other elements has an oxidation number of -2 (negative two) unless it is in a peroxide (O22-) or bonded to F. Examples: O in CO2 is -2 O in LiOH is -2 O in Na3PO4 is -2 What is O in O2? What is O in H2O? Exception: O in H2O2, hydrogen peroxide

Exceptions Halogens that are bonded to other elements have an oxidation number of -1 (negative one) unless they are bonded to a more electronegative element such as a halogen closer to the top of the periodic table. Examples: Cl in NaCl is -1 Cl in PCl5 is -1 Cl in CaCl2 is -1 Exception: Cl in ClF5 is +5, Cl in ClBr6 is -6 while Br in ClBr6 is +1 OK – Let’s face it, the larger halogens are only easily predictable when bonded with a metal, otherwise, much thinking is required!

H in HCl is +1 H in BH3 is -1 Exceptions Hydrogen bonded to a metal is assigned -1, and hydrogen bonded to nonmetal is +1. H in HCl is +1 H in BH3 is -1

DO NOW! Assign oxidation numbers to each element in the element, compound or ion. HCl Mg3N2 KNO3 I2 OH-

Assign oxidation numbers to each element DO NOW! Assign oxidation numbers to each element ClO3- H2O2 Al(NO3)3 PbO2 S8

Assign oxidation numbers to each element. More Practice! Assign oxidation numbers to each element. NaHSO4 m) KMnO4 SO32- n) LiH

More Practice! Assign oxidation numbers to each element in the compounds listed below. o) Fe2O3 p) SO3 q) NH4+ r) H2SO4 s) Na

Review definition of oxidation and reduction. LEO the lion says GER Loss of Electrons is Oxidation _____ Gain of Electrons is Reduction OIL RIG Oxidation Is Loss of electrons causing the oxidation number to pump up to a higher value. Reduction Is Gain of electrons causing a reduction in the value of the oxidation number.

Example 1: Identify the movement of the electron(s) and then label the reaction as oxidation or reduction: Al  Al+3 + 3 e-

2Br - + Cl2  Br2 + 2Cl - Example 2: Identify the movement of the electron(s) (If +  - …gained e-. If -  +…lost e-) and then label the reaction as oxidation or reduction: 2Br - + Cl2  Br2 + 2Cl -

Assign oxidation numbers to each element 1) Mg + N2  Mg3N2 Oxidized ___________________ Reduced ___________________ Reducing Agent __________ Oxidizing Agent _________ 2) Fe + O2 → Fe2O3  Oxidized ___________________

Assign oxidation numbers to each element 3) Ca + O2  CaO Oxidized ___________________ Reduced ___________________ Reducing Agent __________ Oxidizing Agent _________ 4) H2 + O2 → H2O

Assign oxidation numbers to each element 5) CH4 + O2  CO2 + H2O Oxidized ___________________ Reduced ___________________ Reducing Agent __________ Oxidizing Agent _________ 6) Cl2 + KI → KCl + I2  

Assign oxidation numbers to each element 7) CaCO3 + HCl → CaCl2 + H2CO3 Oxidized ___________________ Reduced ___________________ Reducing Agent __________ Oxidizing Agent _________ 8) AgNO3 + Cu  Cu(NO3)2 + Ag