Oxidation-Reduction Reactions REDOX Oxidation-Reduction Reactions

Oxidation-Reduction Reactions Electrons transferred 1 atom to another Redox reactions: All single-replacement rxns All combustion rxns

LEO GOES GER!!!

Oxidation = loss of electrons LOSS of ELECTRONS = OXIDATION LEO

Reduction = gain of electrons GAIN of ELECTRONS = REDUCTION GER

REDOX Oxidation & Reduction: complementary reactions occur together & simultaneously or not at all

Oxidation Numbers In Ionic Compounds: # of electrons lost/gained by atom determined by ions that form compound

Assigning Oxidation Numbers

# of free, uncombined element = 0 Rule #1: # of free, uncombined element = 0 Na He O2 N2 S8 Cl2 P

# of monatomic ion = charge of ion Rule # 2: # of monatomic ion = charge of ion Ca+2 = +2 Cl-1 = -1 Al+3 = +3 Remember: Ions form ionic cmpds: CaCl2, Al(NO3)3, etc.

Rule # 3: F always -1 CF4

Rule # 4: H is nearly always +1 except if bonded to metal then -1 H2O, HNO3, H2SO4, LiH, CaH2, NaH

O is nearly always -2 except when: Rule # 5: O is nearly always -2 except when: OF2 - Bonded to F: O is +2 O22- Bonded to peroxide ion: O is -1 (group 1 & 2 metals)

Rule # 6 Sum oxidation # in neutral compound = 0 H2O CO2 NO SO3

Rule # 7 Sum oxidation # in polyatomic ion = charge of ion Sum in SO4-2 = -2 Sum in NO3-1 = -1

Rule # 8 Covalent cmpds: oxidation # more electronegative atom = negative charge if was ion *NH3: N = -3, H = +1 SiCl4: Si = +4, Cl = -1

Assign Oxidation Nos KCl K = +1, Cl = -1 CaBr2 CO Ca = +2, Br = -1 CO2 Al(NO3)3 Na3PO4 H2S NH4+1 SO3-2 K = +1, Cl = -1 Ca = +2, Br = -1 C = +2, O = -2 C = +4, O = -2 Al = +3, O = -2, N = +5 Na = +1, O = -2, P = +5 H = +1, S = -2 N = -3, H = +1 S = +4, O = -2

2) And if you’re lucky you strike oil & it shoots up 4 3 2 1 -1 -2 -3 -4 2) And if you’re lucky you strike oil & it shoots up 1) You dig down with an oil rig

Electrons are Negative! Why use the word “reduced” when electrons are gained? Look at how the oxidation number changes Ex: Cl gains an electron → Cl-1 oxidation # ↓ from 0 to -1; the # was reduced

Writing Equations Even though oxidation & reduction reactions occur together we write separate equations for each process known as Half-Reactions

Reduction Half-Reactions I2 + 2e-  2I-1 O2 + 4e-  2O-2 Half-reactions must demonstrate: conservation of mass & conservation of charge # atoms on left must = # atoms on right total charge on left must = total charge on right Electrons are gained so put on reactant side!

Oxidation Half-reactions K  K1+ + 1e- Fe2+  Fe3+ + 1e- Cu  Cu2+ + 2e- Total Charge on left = Total Charge on right # atoms on left = # atoms on right Electrons are lost so they are put on product side!

Vocabulary Interlude Oxidizing Agent: Substance being reduced Accepts electrons from something else aids oxidation for another species Reducing Agent: Substance being oxidized Loses electrons to something else aids reduction for another species