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5.2 Oxidation Numbers
What we need to learn…
• determine the following:– the oxidation number of an atom in a chemical
species– the change in oxidation number an atom undergoes
when it is oxidized or reduced – whether an atom has been oxidized or reduced by its
change in oxidation number• relate change in oxidation number to gain or loss
of electrons
Oxidation Numbers
HV2O4- V6+
Is the above equation oxidation or reduction?
Oxidation numbers are used to quickly determine if oxidation or reduction has occurred in a redox reaction.
OXIDATION NUMBER: The charge that an atom would possess if the species containing the atom were made up of ions.
Oxidation numbers are a somewhat fictitious concept, but, by using them, we can create half-reactions and use them in situations where no such half-reactions actually exist
The use of both half-reactions and oxidation numbers are simply procedures which can be used to get us to a balanced REDOX equation; whether the half-reactions or oxidation numbers are real is irrelevant.
Rules for Oxidation Numbers Oxidation # 1. All elements are zero:
Rules for Oxidation Numbers Oxidation # 1. All elements are zero:
N2
Rules for Oxidation Numbers Oxidation # 1. All elements are zero:
N2 0
Rules for Oxidation Numbers Oxidation # 1. All elements are zero:
N2 0
Pb
Rules for Oxidation Numbers Oxidation # 1. All elements are zero:
N2 0
Pb 0
Rules for Oxidation Numbers Oxidation # 1. All elements are zero:
N2 0
Pb 0
Na
Rules for Oxidation Numbers Oxidation # 1. All elements are zero:
N2 0
Pb 0
Na 0
Rules for Oxidation Numbers Oxidation # 1. All elements are zero:
N2 0
Pb 0
Na 0
O2
Rules for Oxidation Numbers Oxidation # 1. All elements are zero:
N2 0
Pb 0
Na 0
O2 0
Rules for Oxidation Numbers Oxidation # 2. Ions are their charge
Na+
Rules for Oxidation Numbers Oxidation # 2. Ions are their charge
Na+ +1
Rules for Oxidation Numbers Oxidation # 2. Ions are their charge
Na+ +1
Br-
Rules for Oxidation Numbers Oxidation # 2. Ions are their charge
Na+ +1
Br- -1
Rules for Oxidation Numbers Oxidation # 2. Ions are their charge
Na+ +1
Br- -1
MgSO4
Rules for Oxidation Numbers Oxidation # 2. Ions are their charge
Na+ +1
Br- -1
MgSO4 +2
Rules for Oxidation Numbers Oxidation # 2. Ions are their charge
Na+ +1
Br- -1
MgSO4 +2
Al2O3
Rules for Oxidation Numbers Oxidation # 2. Ions are their charge
Na+ +1
Br- -1
MgSO4 +2
Al2O3 -2
Rules for Oxidation Numbers Oxidation # 3. The oxidation number of O
in a compound is –2.
Na2O
Rules for Oxidation Numbers Oxidation # 3. The oxidation number of O
in a compound is –2.
Na2O -2
Rules for Oxidation Numbers Oxidation # 3. The oxidation number of O
in a compound is –2.
Na2O -2
CO2
Rules for Oxidation Numbers Oxidation # 3. The oxidation number of O
in a compound is –2.
Na2O -2
CO2 -2
Rules for Oxidation Numbers Oxidation # 3. The oxidation number of O
in a compound is –2.
Na2O -2
CO2 -2
O2
Rules for Oxidation Numbers Oxidation # 3. The oxidation number of O
in a compound is –2.
Na2O -2
CO2 -2
O2 0
Rules for Oxidation Numbers Oxidation # 3. The oxidation number of O
in a compound is –2.
Na2O -2
CO2 -2
O2 0
CH3COOH
Rules for Oxidation Numbers Oxidation # 3. The oxidation number of O
in a compound is –2.
Na2O -2
CO2 -2
O2 0
CH3COOH -2
Rules for Oxidation Numbers Oxidation # 3. The oxidation number of O
in a compound is –2 or inperoxides -1.
Na2O -2
CO2 -2
O2 0
CH3COOH -2
HOOH
Rules for Oxidation Numbers Oxidation # 3. The oxidation number of O
in a compound is –2 or inperoxides -1.
Na2O -2
CO2 -2
O2 0
CH3COOH -2
HOOH exception -1
Rules for Oxidation Numbers Oxidation # 4. The oxidation number for H
in a compound is +1.
Rules for Oxidation Numbers Oxidation # 4. The oxidation number for H
in a compound is +1.
H2O
Rules for Oxidation Numbers Oxidation # 4. The oxidation number for H
in a compound is +1.
H2O +1
Rules for Oxidation Numbers Oxidation # 4. The oxidation number for H
in a compound is +1
H2O +1
C12H24O11
Rules for Oxidation Numbers Oxidation # 4. The oxidation number for H
in a compound is +1
H2O +1
C12H24O11 +1
Rules for Oxidation Numbers Oxidation # 4. The oxidation number for H
in a compound is +1
H2O +1
C12H24O11 +1
H2
Rules for Oxidation Numbers Oxidation # 4. The oxidation number for H
in a compound is +1
H2O +1
C12H22O11 +1
H2 0
Rules for Oxidation Numbers Oxidation # 4. The oxidation number for H
in a compound is +1 or inmetal hydrides -1.
H2O +1
C12H24O11 +1
H2 0
NaH
Rules for Oxidation Numbers Oxidation # 4. The oxidation number for H
in a compound is +1 or inmetal hydrides -1.
H2O +1
C12H24O11 +1
H2 0
NaH -1
Rules for Oxidation Numbers Oxidation # 5.All alkali and Alkali Earth metals within a
chemical species will be their traditional combining capacity (group 1 [= +1] and 2 [+2] on PT)
6. Most often the halogens (group 17) will be their traditional charge within a chemical species (-1)
NaCl (+1 and -1 respectively)
HClO3 (+1, +5* and -2 respectively) *not always -1
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
SO42-
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
oxidation #s
SO42-
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
oxidation #s -2
SO42-
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
oxidation #s -2
SO42-
Total charge
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
oxidation #s -2
SO42-
Total charge -8
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
oxidation #s -2
SO42-
Total charge -8 = -2
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
oxidation #s -2
SO42-
Total charge +6 -8 = -2
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
oxidation #s +6 -2
SO42-
Total charge +6 -8 = -2
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
oxidation #s +6 -2 +6
SO42-
Total charge +6 -8 = -2
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
PO43-
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
oxidation #s
PO43-
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
oxidation #s -2
PO43-
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
oxidation #s -2
PO43-
Total charge
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
oxidation #s -2
PO43-
Total charge -8
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
oxidation #s -2
PO43-
Total charge -8 = -3
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
oxidation #s -2
PO43-
Total charge +5 -8 = -3
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
oxidation #s +5 -2
PO43-
Total charge +5 -8 = -3
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
oxidation #s +5 -2 +5
PO43-
Total charge +5 -8 = -3
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
Cr2O72-
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
oxidation #s
Cr2O72-
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
oxidation #s -2
Cr2O72-
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
oxidation #s -2
Cr2O72-
Total charge
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
oxidation #s -2
Cr2O72-
Total charge -14
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
oxidation #s -2
Cr2O72-
Total charge -14 = -2
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
oxidation #s -2
Cr2O72-
Total charge +12 -14 = -2
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
oxidation #s -2
Divide by 2 Cr2O72-
Total charge +12 -14 = -2
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
oxidation #s +6 -2
Cr2O72-
Total charge +12 -14 = -2
Rules for Oxidation Numbers 5. All other oxidation numbers are assigned so that the
sum of all of the oxidation numbers is equal to the charge on the chemical species.
Oxidation #
oxidation #s +6 -2 +6
Cr2O72-
Total charge +12 -14 = -2
Oxidation #
Ca(NO3)2
Oxidation #
+2
Ca(NO3)2
Oxidation #
+2
Ca(NO3)2 +2
Oxidation #
Na2C2O4
Oxidation #
+1 -2
Na2C2O4 +2 -8 = 0
Oxidation #
+1 -2
Na2C2O4 +2 +6 -8 = 0
Oxidation #
+1 +3 -2
Na2C2O4 +3+2 +6 -8 = 0
Oxidation #
CH3COOH
Oxidation #Rewrite
C2H4O2
Oxidation #Rewrite +1 -2 0
C2H4O2 +4 -4 = 0
Oxidation #
Zn(OH)42-
Oxidation #
+2 -2 +1 +2
Zn(OH)42-
+2 -8 +4 = -2
Oxidation #
H2PtCl6
Oxidation #
+1 +4 -1 +4
H2PtCl6 +2 +4 -6 = 0
Oxidation #
Na2O2
Oxidation #
+1 -2
Na2O2 +2 -4 = 0
Exception - does not work, O must be -1
Oxidation #
+1 -1 -1
Na2O2 +2 -2 = 0
Exception - does not work, O must be -1
Oxidation #
CaH2
Oxidation #
+2 +1
CaH2 +2 +2 = 0
Exception - does not work, H must be -1
Oxidation #
+2 -1 -1
CaH2 +2 -2 = 0
Exception - does not work, H must be -1
Oxidation Numbers
Using oxidation numbers in REDOX equations:
HV2O4- V6+
Is the above equation oxidation or reduction?
Oxidation Numbers
+3 +6HV2O4
- V6+
Is the above equation oxidation or reduction?
Oxidation Numbers
Increase
+3 +6HV2O4
- V6+
Is the above equation oxidation or reduction?
If the oxidation number increases it is oxidation.
Homework….
• Read SWB pages 193 -195• Do exercises #3-5 page 194 and # 6 page
195
