Download Oxidation Number Exercise

Page 57
Oxidation Number Exercise - answers
Oxidation Number Exercise
Do not hand in this work sheet. When you are ready, you will be given an examination over this
material. Complete the examination by yourself and hand it in to receive credit.
Purpose: This exercise is designed to teach the student how to assign oxidation numbers.
Oxidation numbers are very important and are used for 1) naming compounds, 2) balancing
oxidation-reduction reactions, 3) calculations in electrochemistry and other areas of chemistry.
Rule 0
The following rules are in the form of a hierarchy; that is, the first stated rule takes
precedence over subsequent rules if a conflict arises.
Rule 1
The oxidation numbers for all the atoms in a neutral molecule must add up to 0.
Similarly, the oxidation numbers for all the atoms of an ion must add up to the
charge of the ion. (You are expected to recognize polyions. For the common
polyions, know their charges and their names. A summary of the common
polyions appears at the end of this exercise. The first step is, always, to determine
what polyions are present.)
Rule 1a
The oxidation number of elements in the elemental form is 0. (Note - this rule is a
direct consequence of rule 1. How so?)
Rule 1b
The oxidation number of any monatomic ion is the same as its charge. (See
comment in 1a.)
Exercises - Give the oxidation number for the following atoms:
O2
O= 0
F2
F= 0
S8
S= 0
Cl2
Cl = 0
N2
N= 0
Al
Al = 0
Co2+
Co = +2
Mn2+
Mn = +2
Cl!
Cl = !1
Cr3+
Cr = +3
I3!
I = !1/3
Hg2+2
Hg = +1
_
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Oxidation Number Exercise - answers
Rule 2 Fluorine has an oxidation number of !1.
Exercises - Give the oxidation number for the following atoms:
NaF
Na = +1
IF3
I = +3
ClF2!
Cl = +1
SF4
S = +4
PF3
P = +3
SF62!
S = +4
PF5
P = +5
PF63!
P = +3
W2F93! W = +3
OF2
O = +2
NF3
N = +3
F2
Rule 3
The metal of groups IA have an oxidation number of +1
The metal of groups IIA have an oxidation number of +2
Sc, Y and Al have an oxidation number of +3.
F= 0
Exercises - Give the oxidation number for the following atoms:
Na2O
Na = +1
Na2O2
O = !1
KO2
K = -1/2
NaOH
Na = +1
ScH3
H = !1
LiH
H = !1
CaC2
C = !1
CaMgO2 O = !2
MgH2
H = !1
MgF2
Mg = +2
RbO2
O = -1/2
MgSF6
S = +4
NaPF6
P = +5
LiBF4
B = +3
Rule 4
Hydrogen has an oxidation number of +1 when combined with elements on the right
side of the periodic chart (non-metals) and a !1 when combined with elements on the
left side of the periodic chart (metals).
Exercises - Give the oxidation number for the following atoms:
HCl
Cl = !1
HF
F = !1 rule 2(why)
NaOH
O = !2
HI
I = !1
UH3
U = +3
NH4+
N = !3
PH3
P = !3
H2SF6
S = +4
NH3
N = !3
AsH3
As = !3
ScH3
Sc = +3
HPF4
P=
H3O+
O = !2
OH!
O = !2
+3
Page 59
Oxidation Number Exercise - answers
Rule 5
Oxygen has an oxidation number of !2. (Note: Your knowledge of the polyions is
now needed. See page 6.)
Cautionary Note: Review Rule 0
Exercises - Give the oxidation number for the following atoms:
Co(ClO)2 Co = +2
Cl = +1
Na2O2
Na = +1
O = !1
CoCrO4
Co = +2
AgNO3 Ag = +1
N = +5
O = -2
H2SO4
S = +6
O = !½
ClO4!
Cl = +7
K = +1
NH4OHN = !3
Cr = +6
Mg(OH)2 Mg =
RbO2
Rb
+2
+1
KMnO4= Mn = +7
OF2
F = !1
KO2
K=
IO2!
I = +3
+1
IO3!
O=
!½
I = +5
K2Cr2O7 Cr = +6
BrO2!
Br = +3
Zn(NO2)2 Zn = +2
Cautionary Note: Review Rule 0 again
Rule 6
Rule 7
Rule 8
Group VIIA atoms have an oxidation number of -1.
Group VIA atoms have an oxidation number of -2.
Group VA atoms have an oxidation number of -3.
Exercises - Give the oxidation number for the following atoms:
PH3
P = !3
CH3NH2
C = !2
CN!
C = +2
BF3NH3
B = +3
MnCl4
Mn = +4
W2Cl93!
W = +3
Co3N2
Co = +2
NCl3
N = +3
KSCN
C = +4
HCN
C = +2
POCl3
P = +5
V3N4
V = +4
Page 60
Oxidation Number Exercise - answers
Additional (Optional) Exercises:
NH3
N = !3
As2O5
As = +5
SiF4
Si = +4
HNO3
N = +5
N2H4
N = !2
PCl6!
P = +5
MnO2
Mn = +4
CrCl3
Cr = +3
Cr2O72!
Cr = +6
AgCH3COO Ag = +1
N2O
N = +1
N2O5
N = +5
Au2O
Au = +1
AuO
Au = +2
CuSO4
Cu = +2
Os2O5
Os = +5
Fe3O4
Fe = +8/3
Fe2O3
Fe = +3
FeO
Fe = +2
FePO4
Fe = +3
SiO2
Si = +4
H2S
S = !2
FeS
S = !2
NaHCO3
C = +4
AuHCO3 Au = +1
ScAsO4
As = +5
NH4OH
N = !3
SO3
S = +6
H2CrO4
Cr = +6
H4P2O7
P = +5
Cl2
Cl = 0
S2O32-
S = +2
MgC2
C = !1
S2Cl2
S = +1
Cr2(CO3)3 Cr = +3
K3FeO4
Fe = +5
S8
S= 0
BO2!
B = +3
Al2O3
Al = +3
RbO2
O = !1/2
I3!
I = !1/3
Th4H11
Th = +11/4
NaHSO4
S = +6
Ag2CrO4 Ag = +1
RbH
H = !1
Na2HPO4 P = +5
Eu3(PO3)2 P = +3
B4O72!
B = +3
P4O6
BeF2
P4O10
P = +5
P = +3
Be = +2
OF2
F = !1
O = +2
Ce(ClO3)2
Ce = +2
Cl = +5
Fe(MnO4)2 Mn = +7
NaSCN
S = !2
Fe = +2
C = +4
N = !3