Electrochemistry Lesson 3 Oxidation Numbers

Ho Ho Ho Silver crystals on a copper frame

Oxidation Numbers   HV2O4-  V6+ Is the above equation oxidation or reduction? Oxidation numbers are assigned numbers that are used to determine if oxidation or reduction has occurred.

Rules for Oxidation Numbers Oxidation #   1. All elements are zero: N2 Pb Na O2

Rules for Oxidation Numbers Oxidation #   2. Monatomic Ions are their charge Na+ +1 -1 Br- +2 MgSO4 -2 Al2S3

Rules for Oxidation Numbers Oxidation #   3. O in a compound is -2 exception: peroxides -1 Na2O -2 CO2 -2 O2 CH3COOH -2 -1 exception HOOH

Rules for Oxidation Numbers Oxidation #   4. H in a compound is +1 exception: metal hydrides -1 H2O +1 +1 C12H22O11 H2 -1 NaH

oxidation #s SO42- Total charge +6 -2 -2 x 4 +6 -8 = -2 Rules for Oxidation Numbers   5. The sum of the oxidation numbers must equal the charge oxidation #s SO42- Total charge +6 -2 -2 x 4 +6 -8 = -2

oxidation #s PO43- Total charge +5 -2 +5 -8 = -3

oxidation #s Cr2O72- Total charge +6 -2 12 / 2 +12 -14 = -2

Ca(NO3)2 +2

Na2C4O8 +1 +7/2 -2 +2 +14 -16 = 0

CH3COOH

Rewrite C2H4O2 +1 -2 +4 -4 = 0

Zn(OH)42- +2 -2 +1 +2 -8 +4 = -2

H2PtCl6 +1 +4 -1 +2 +4 -6 = 0

H3PO3 +1 +3 -2 +3 +3 -6 = 0

Al(NO3)3 +3 +5 -2 +3 +15 -18 = 0

Na2O2 Exception - does not work, O must be -1 +1 -1 -2 +2 -2 -4 = 0

CaH2 +2 +1 -1 +2 +2 -2 = 0 Exception - does not work, H must be -1

Fe(H2O)5(OH)2+

0 -1 Fe(H2O)5(OH)2+ ? + 0 -1 = +2

+3 0 -1 Fe(H2O)5(OH)2+ +3 + 0 -1 = +2

Is the above equation oxidation or reduction? Oxidation Numbers   HV2O4-  V6+ Is the above equation oxidation or reduction? Increase +6 +3 If the oxidation number increases it is oxidation.

Using Oxidation Numbers   If the oxidation number of the central atom increases going from left to right, its oxidation. ClO2-  ClO4- Increase is oxidation +3 +7 oxidation reducing agent 4 electrons lost

Using Oxidation Numbers   If the oxidation number of the central atom decreases going from left to right, its reduction. NO3-  HNO2 +5 +3 decrease is reduction reduction 2 electrons gained oxidizing agent

Label the oxidizing agent and the reducing agent.   +7 +1 +5 0 ReO4- + IO-  IO3- + Re Reduced Oxidized Ox Agent Red Agent

Label the oxidizing agent and the reducing agent. +3 +5 +5 +2   +3 +5 +5 +2 3As2O3 + 4NO3- + 7H2O + 4H+  6H3AsO4 + 4NO oxidized reduced red agent ox agent Numa Numa