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Electrochemistry Lesson 3 Oxidation Numbers. Ho Ho Ho. Silver crystals on a copper frame. Oxidation Numbers HV 2 O 4 - V 6+ Is the above equation oxidation or reduction? Oxidation numbers are assigned numbers that are used to determine if oxidation or reduction has occurred. - PowerPoint PPT Presentation
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ElectrochemistryLesson 3
Oxidation Numbers
Silver crystals on a copper frame
Ho Ho Ho
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 0
Pb 0
Na 0
O2 0
Rules for Oxidation Numbers Oxidation # 2. Monatomic Ions are their charge
Na+ +1
Br- -1
MgSO4+2
Al2S3
-2
Rules for Oxidation Numbers Oxidation # 3. O in a compound is -2
exception: peroxides -1
O2 0
Na2O -2CO2 -2
CH3COOH -2exceptionHOOH -1
Rules for Oxidation Numbers Oxidation # 4. H in a compound is +1
exception: metal hydrides -1
H20
H2O +1
C12H22O11+1
NaH -1
Rules for Oxidation Numbers 5. The sum of the oxidation numbers must equal the
charge
oxidation #s
SO42-
Total charge= -2
-2
-8+6
+6
-2 x 4
oxidation #s
PO43-
Total charge= -3
-2
-8+5
+5
oxidation #s
Cr2O72-
Total charge= -2
-2
-14+12
12 / 2
+6
Ca(NO3)2
+2
Na2C4O8 = 0
-2
-16
+1
+2 +14
+7/2
CH3COOH
Rewrite
C2H4O2 = 0
-2
-4
+1
+40
0
Zn(OH)42-
= -2
+1
+4
-2
-8+2
+2
H2PtCl6 -1
= 0-6
+1 +4
+2 +4
H3PO3 = 0
-2
-6
+1 +3
+3 +3
Al(NO3)3 = 0
-2
-18
+3 +5
+3 +15
Na2O2
Exception - does not work, O must be -1
= 0
+1 -2
+2 -4
-1
-2
CaH2 -1+1
+2 = 0+2
+2
-2
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
Oxidation Numbers
HV2O4
- V6+
Is the above equation oxidation or reduction?
+6+3
Increase
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
oxidation
4 electrons lostreducing agent
+3 +7
Using Oxidation Numbers
If the oxidation number of the central atom decreases going from left to right, its reduction.
NO3- HNO2
decrease is reduction
reduction
2 electrons gainedoxidizing agent
+5 +3
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 3As2O3 + 4NO3
- + 7H2O + 4H+ 6H3AsO4 + 4NO
oxidized reduced
red agent ox agent
Numa Numa