# Reduction - Oxidation Reduction Oxidation Chapters 20 + 21 Oxidation Numbers (States) Positive, negative or neutral values assigned to an atom to keep track of the number of electrons lost or gained. Charge Oxidation Number Rules

Elements alone (not in a compound) = 0 Example: Cu, N2 Monatomic ion (single atom) = charge Example:

Na+, Cl-, Mg+2, O-2 Oxidation Number Rules Compound Example: H2O

sum of all atoms = 0 H+H+O=0 Polyatomic ion sum of all atoms = charge Example: NO3-

N + O + O + O = -1 Common Oxidation Numbers Group 1 +1 Group 2 +2 Group 13 +3 Group 15 -3 Group 16 -2 Group 17 -1 Some

exceptions to each above Redox Reactions Reduction Oxidation, or redox, involves the transfer of electrons Reduction gain of electrons

Oxidation loss of electrons Redox Reactions LEO goes GER

Lose Electrons Oxidation Gain Electrons Reduction Redox Reaction 0 Mg 0

+2 -1 + Cl2 MgCl2 Mg - lost electrons (oxidation) Cl gained electrons (reduction)

Redox Reaction 0 2Al Al Ni +2 +5 -2

0 +3 +5 -2 + 3Ni(NO3)2 3Ni + 2Al(NO3)3 - lost electrons (oxidation) gained electrons (reduction) Redox Reaction

Zn + CuSO4 Cu + ZnSO4 One element loses electrons (oxidation) One element gains electrons (reduction) All other ions are spectators Net Ionic Equation Shows only the ions involved in the redox reaction, not spectator ions

Still shows conservation of mass and charge Zn + CuSO4 Cu + ZnSO4 Zn + Cu+2 Cu + Zn+2

Net Ionic Example Zn + 2HCl H2 + ZnCl2 Zn + 2H+ H2 + Zn2+ Half Reactions

Only shows one element and how many electrons are gained or lost Must maintain conservation of mass and charge Half Reactions Zn + CuSO4 Cu + ZnSO4

Zn + Cu+2 Cu + Zn+2 Zn Zn+2 + 2e- Cu2+ + 2e- Cu

Net Ionic Oxidation Reduction Oxidation Loss of Electrons

Examples: Zn 2Cl- Zn+2 + 2e Cl2 + 2e- Reduction Gain of electrons

Examples: Ag+ Cl2 + e- Ag + 2e- 2Cl- Balancing Reactions

The number of electrons lost must equal the number of electrons gained Example: 2Na + ZnCl Zn + 2NaCl 2 + 2e- Zn 2(Na Na + + e- ) Zn+2

Balancing Example Ti+4 + 4e 2(Cu+2 + 2e- Cu) Ti Ti + 2Cu+2 Ti+4 + 2Cu Ti + 2CuCl2 TiCl4 + 2Cu

Spontaneous Reactions More active element does not want to be alone Table J Metal being oxidized must be ABOVE

metal being reduced for spontaneous reactions to occur Reversed for Nonmetals Spontaneous Reactions Examples: Zn + CuSO Cu + ZnSO 4 4

YES NO CaSO4 + Mg Ca + MgSO4 Zn + 2HCl H2 + ZnCl2 YES

YES F2 + 2NaI I2 + 2NaF Electrochemical Cells any device that converts chemical energy into electrical energy or electrical energy into chemical energy

Two types Voltaic (Chemical) Electrolytic Electrochemical Cells

Electrode metal conductor in an electrical circuit that carries electrons to or from another substance Cathode electrode where reduction takes place Anode electrode where oxidation takes place Voltaic Cell

Flow of electrons is spontaneous based on electronegativity and ionization energy Chemical energy is converted to electrical energy Examples: Batteries

Voltaic Cell Electrochemical Cell Components Salt Bridge Allows

for the passage of ions, not electrons Switch Device that opens(turns off) and closes(turns on) circuit Voltaic Cell Electrolysis

Process in which electrical energy is converted to chemical energy Example: 2H2O 2H2 + O2 Electrolytic Cells

Electrons are pushed by an outside power source Electrical energy is converted to chemical energy

Examples: Electroplating, Electropolishing Electrolytic Cell Voltaic or Electrolytic? Zn + NiCl2 Ni + ZnCl2 Voltaic Electrolytic

Cu + ZnSO4 Zn + CuSO4 Zn + NiCl2 Ni + ZnCl2 Voltaic Electrolytic

2H2O 2H2 + O2 Electrolytic 2NaCl 2Na + Cl2