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Date! !
Block! !
Balancing Redox Reactions
A. Identify the change in oxidation number of the designated element and determine if the change
is due to oxidation or reduction.
1. ! ! !
Sulfur in S2O8 ---> SO42-
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The oxidation number changes from ! !
!
This is an example of: !
2. ! ! !
oxidation!!
Phosphorus in P4 ---> H2PO42-!!
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The oxidation number changes from
!
This is an example of: !
3. ! ! !
(note: P4 is the elemental state for phosphorus)
!!
oxidation!!
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Nitrogen in N2O4 ---> NO !
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This is an example of: !
oxidation!!
to ! !
!
reduction
Technetium in TcO42- ---> Tc2+
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The oxidation number changes from
!
This is an example of: !
!
!
to ! !
reduction
The oxidation number changes from ! !
5. ! ! !
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reduction
!
4. ! ! !
to ! !
oxidation!!
!!
to ! !
!
reduction
Tungsten in WO3 ---> W3O8 (note: oxidation numbers are not always whole numbers)
The oxidation number changes from ! !
to ! !
This is an example of: ! oxidation!! reduction
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1
6. ! ! !
Chromium in Cr2O72- ---> Cr3+
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The oxidation number changes from ! !
!
This is an example of: !
7. ! ! !
oxidation!!
Manganese in MnO4- ---> MnO2
The oxidation number changes from ! !
!
This is an example of: !
oxidation!!
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Chlorine in Cl- ---> ClO3-
The oxidation number changes from ! !
!
This is an example of: !
oxidation!!
to ! !
!
reduction
Sulfur in HSO3- ---> S2O62-
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The oxidation number changes from ! !
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This is an example of: !
10. !! !
to ! !
reduction
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9. ! ! !
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reduction
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8. ! ! !
to ! !
oxidation!!
to ! !
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reduction
Nitrogen in NO3- ---> NH4+
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The oxidation number changes from ! !
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This is an example of: !
oxidation!!
to ! !
!
reduction
2
B. Half-Reactions
Write unbalanced oxidation and reduction half-reactions represented in each of the following
redox equations. Write the half-reactions in net ionic form if they occur in aqueous solutions,
removing any spectator ions.
11. !
PbO(s) !
+
NH3(g)! ----->
N2(g)!+!
H2O(l)!+!
Pb(s)
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Oxidation half-reaction:!
!
!
!
!
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!
!
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Reduction half-reaction:!
!
!
!
!
!
!
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12. !
I2(s)! +!
+!
NaI(aq)
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Oxidation half-reaction:!
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Reduction half-reaction:!
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13. !
Sn(s)! +!
----->! SnCl2(aq)!
+!
H2(g)
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Oxidation half-reaction:!
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Reduction half-reaction:!
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Na2S2O3(aq)! -----> Na2S2O4(aq)!!
2HCl(aq)!
C . Acidic Solutions
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Use the half-reaction method to balance the following redox equations that
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take place in an acidic solution.
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When complete, box the oxidizing agent and underline the reducing agent.
14.!
H2S(g)
+
Cl2(g)
----->!
S(s)! +!
Cl-(aq)
3
15.!
Ce4+(aq)
16.!
BiO3 -(aq)
+
+
ClO3-(aq)
Mn2+(aq)
----->!Ce3+(aq)!
----->
ClO4-(aq)
+!
MnO4-(aq)
+
Bi3+(aq)
4