WarmUp: Oxidation Review

1
WarmUp Oxidation Review
In one of Ms. Lyalls 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.
2
WarmUp Oxidation Review
In one of Ms. Lyalls favorite reactions, solid
zinc combines with solid sulfur to produce zinc
sulfide. Here is the skeleton equation
loses 2 e-
2
0
-2
0
Zn(s) S(s) ?? ZnS(s)
gains 2 e-
a. Label the oxidation number of each 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.

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.
b. Label the species that is oxidized and which
is is reduced.
c. Label the oxidizing and the reducing agents
3
Try to balance this skeleton equation
HNO3(aq) H3AsO3(aq) --gt NO(g) H3AsO4(aq)
H2O(l)
It can be done. But its not easy to do by trial
and error.
4
Balancing Equations Using Oxidation Numbers
Oxidation numbers can help you!
X 3 6 electrons lost
loses 2 e-
1
1
1
-2
5
-2
5
-2
-2
-2
1
3
2
HNO3(aq) H3AsO3(aq) --gt NO(g)
H3AsO4(aq) H2O(l)
2
3
X 2 6 electrons gained
gains 3 e-
1. Label the oxidation number of each species.
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.
4. Determine the ratio needed to balance
electrons lost with electrons gained.
Use that ratio to write locked coefficient ratio.
5
Balancing Equations Using Oxidation Numbers
Now that you have locked the ratio between HNO3
and H3AsO3, the equation is easy to balance.
2
3
HNO3(aq) H3AsO3(aq) --gt NO(g)
H3AsO4(aq) H2O(l)
2
3
11
11
______ H ______ ______ N ______ ______ O
______ ______ As ______
2
2
15
15
3
3
6
Balancing Equations Using Oxidation Numbers
Oxidation numbers can help you!
X 3 6 electrons lost
loses 2 e-
-2
5
1
-2
1
-2
2
-2
5
0
2
Cu(s) HNO3(aq) --gt Cu(NO3)2(aq) NO(g)
H2O(l)
3
2
X 2 6 electrons gained
gains 3 e-
1. Label the oxidation number of each species.
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.
4. Determine the ratio needed to balance
electrons lost with electrons gained.
Use that ratio to write locked coefficient ratio.
7
Balancing Equations Using Oxidation Numbers
3
4
8
Cu(s) HNO3(aq) --gt Cu(NO3)2(aq)
NO(g) H2O(l)
2
3
3
3
______ Cu ______ ______ N ______ ______ O
______ ______ H ______
8
8
24
24
8
8
8
Balancing Equations Using Oxidation Numbers
Oxidation numbers can help you!
X 5 10 electrons lost
loses 2 e-
-2
6
1
1
-2
6
-2
4
1
1
2
6
-2
6
1
-2
-2
-2
1
7
1
KMnO4 H2SO4 NaHSO3 ? MnSO4 K2SO4
Na2SO4 H2O
5
2
X 2 10 electrons gained
gains 5 e-
1. Label the oxidation number of each species.
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.
4. Determine the ratio needed to balance
electrons lost with electrons gained.
Use that ratio to write locked coefficient ratio.
9
Balancing Equations Using Oxidation Numbers
2
KMnO4 H2SO4 NaHSO3 ? MnSO4 K2SO4
Na2SO4 H2O
5
2
2
2
______ Mn ______ ______ K ______ ______ Na
______ ______ S ______ ______ H ______ ______ O
______
Because of the even subscript for Na in the
product you need to double everything
2
2
5
10
Balancing Equations Using Oxidation Numbers
Na2SO4 is locked
2
4
5
6
KMnO4 H2SO4 NaHSO3 ? MnSO4 K2SO4
Na2SO4 H2O
10
4
4
4
______ Mn ______ ______ K ______ ______ Na
______ ______ S ______ ______ H ______ ______ O
______
All the S in product is locked.
4
4
10
10
Because of the even subscript for Na in the
product you need to double everything
13
13
12
16
50
50
11
Balancing Equations Using Oxidation NumbersTry
this one on your own
K2Cr2O7 6NaI 7H2SO4 ? Cr2(SO4)3 3I2
7H2O 3Na2SO4 K2SO4