1. Redox Reactions

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

3. 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

4. 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.

5. 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.

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

7. Examples Photosynthesis Cellular Respiration
6CO H2O  C6H12O O2
Cellular Respiration
6O2 + C6H12O6  6CO H2O

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

9. LEO goes GER
Listen to him ROAR!!

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

11. 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.

12. 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

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

14. 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)

15. 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-)

16. 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

17. 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!

18. 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

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

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

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

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

23. 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.

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

25. 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 -

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

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

28. Assign oxidation numbers to each element
5) CH O2  CO H2O
Oxidized ___________________
Reduced ___________________
Reducing Agent __________ Oxidizing Agent _________
6) Cl KI → KCl I2

29. Assign oxidation numbers to each element
7) CaCO HCl → CaCl H2CO3
Oxidized ___________________
Reduced ___________________
Reducing Agent __________ Oxidizing Agent _________
8) AgNO Cu  Cu(NO3) Ag