WarmUp: Oxidation Review In one of Ms. Lyall’s favorite reactions, solid zinc combines with solid...
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Transcript of WarmUp: Oxidation Review In one of Ms. Lyall’s favorite reactions, solid zinc combines with solid...
WarmUp: Oxidation ReviewIn one of Ms. Lyall’s favorite reactions, solid zinc combines with solid sulfur to produce zinc sulfide. Here is the skeleton equation
Zn(s) + S(s) ZnS(s)
a. Label the oxidation number of each species.
b. Label the species that is oxidized and which is is reduced.
c. Label the oxidizing and the reducing agents
d. Determine how many electrons were lost by each atom of the oxidized species. Draw an arrow from the oxidized reactant to the oxidized product and label the arrow with the number of electrons lost each atom. Repeat for the reduced species.
WarmUp: Oxidation ReviewIn one of Ms. Lyall’s favorite reactions, solid zinc combines with solid sulfur to produce zinc sulfide. Here is the skeleton equation
Zn is oxidized
S is reduced
Zn is the reducing agent
S is the oxidizing agent
Zn(s) + S(s) ZnS(s)
a. Label the oxidation number of each species.
0 0 +2 -2
b. Label the species that is oxidized and which is is reduced.
c. Label the oxidizing and the reducing agents
loses 2 e-
gains 2 e-
d. Determine how many electrons were lost by each atom of the oxidized species. Draw an arrow from the oxidized reactant to the oxidized product and label the arrow with the number of electrons lost each atom. Repeat for the reduced species.
e. The number of electrons lost by the reducing agent must equal the number of electrons gained by the oxidizing agent. You can use this ratio to help you balance a redox reaction equation.
Try to balance this skeleton equation:
HNO3(aq) + H3AsO3(aq) --> NO(g) + H3AsO4(aq) + H2O(l)
It can be done.But it’s not easy to do by trial and error.
Balancing Equations Using Oxidation NumbersOxidation numbers can help you!
As is oxidized
N is reduced
HNO3(aq) + H3AsO3(aq) --> NO(g) + H3AsO4(aq) + H2O(l)
1. Label the oxidation number of each species.
+1 -2+5 +1
2. Label which species is oxidized and which is is reduced.3. Determine how many electrons are “lost” by each oxidized atom and how many are “gained” by each reduced atom.
loses 2 e-
gains 3 e-
-2+3 -2+2 +1 -2+5 +1 -2
4. Determine the ratio needed to balance electrons lost with electrons gained.
X 3 = 6 electrons lost
X 2 = 6 electrons gained
Use that ratio to write locked coefficient ratio.
2 3
Balancing Equations Using Oxidation NumbersNow that you have locked the ratio between HNO3 and H3AsO3, the equation is easy to balance.
HNO3(aq) + H3AsO3(aq) --> NO(g) + H3AsO4(aq) + H2O(l)2 3
______ H ____________ N ____________ O ____________ As ______
2
2
2
3
3
3
11 11
15 15
Balancing Equations Using Oxidation NumbersOxidation numbers can help you!
Cu is oxidized
Some N is reduced
Cu(s) + HNO3(aq) --> Cu(NO3)2(aq) + NO(g) + H2O(l)
1. Label the oxidation number of each species.
0 +1
2. Label which species is oxidized and which is is reduced.3. Determine how many electrons are “lost” by each oxidized atom and how many are “gained” by each reduced atom.
loses 2 e-
gains 3 e-
-2+5 -2+5 +2-2 +1 -2
4. Determine the ratio needed to balance electrons lost with electrons gained.
X 3 = 6 electrons lost
X 2 = 6 electrons gained
Use that ratio to write locked coefficient ratio.
23
+2
Balancing Equations Using Oxidation Numbers
Cu(s) + HNO3(aq) --> Cu(NO3)2(aq) + NO(g) + H2O(l)23______ Cu ____________ N ____________ O ____________ H ______
33
38
8
824
4
248 8
Balancing Equations Using Oxidation NumbersOxidation numbers can help you!
Some S is oxidized
Mn is reduced
KMnO4+ H2SO4+ NaHSO3 MnSO4+ K2SO4 + Na2SO4 + H2O
1. Label the oxidation number of each species.
-2
2. Label which species is oxidized and which is is reduced.3. Determine how many electrons are “lost” by each oxidized atom and how many are “gained” by each reduced atom.
loses 2 e-
gains 5 e-
-2+6 -2+4 -2+2 +6-2
4. Determine the ratio needed to balance electrons lost with electrons gained.
X 5 = 10 electrons lost
X 2 = 10 electrons gained
Use that ratio to write locked coefficient ratio.
52
+7+1 +1 +1+1 +6 +1 -2+6+1 -2+1
Balancing Equations Using Oxidation Numbers
KMnO4+ H2SO4+ NaHSO3 MnSO4+ K2SO4 + Na2SO4 + H2O52
______ Mn ____________ K ____________ Na ____________ S ____________ H ____________ O ______
22
22 25
Because of theeven subscriptfor Na in the product youneed to doubleeverything
Balancing Equations Using Oxidation Numbers
KMnO4+ H2SO4+ NaHSO3 MnSO4+ K2SO4 + Na2SO4 + H2O104
______ Mn ____________ K ____________ Na ____________ S ____________ H ____________ O ______
44
44
2
410
Na2SO4
is locked
All the S inproduct is locked.
Because of theeven subscriptfor Na in the product youneed to doubleeverything
5
101313
12
6
1650 50
Balancing Equations Using Oxidation NumbersTry this one on your own
K2Cr2O7 + 6NaI + 7H2SO4
Cr2(SO4)3 + 3I2 + 7H2O + 3Na2SO4 + K2SO4