Transcript Worked Examples: Chapter 8

Chapter 8 Worked Example 1
The decavanadate ion is a complex species with chemical
formula V10O286-. It reacts with an excess of acid to form the
dioxovanadium ion VO2+, and water. Write a balanced
equation and state the oxidation state of vanadium before and
after reaction. Which vanadium oxide has the same oxidation
state of V?
Solution
V10O286- + 16H+
10 VO2+ + 8H2O
Oxidation state of V in both species is +5 {V(V)}
V2O5 is the V(V) oxide
Chapter 8 Worked Example 2
Determine the oxidation state of the metal in each of the
Following coordination complexes:
[V(NH3)4Cl2], [Mo2Cl8]4-, [Co(H2O)2NH3Cl3]-,
[Ni(CO)4]
Solutions
[V(NH3)4Cl2]
V = +2
[Mo2Cl8]4- [Co(H2O)2NH3Cl3]- [Ni(CO)4]
Mo = +2
Co = +2
Ni = 0
Chapter 8 Worked Example 3
Give the chemical formula that corresponds to each of
the following compounds.
(a) Sodium tetrahydroxozincate (II)
(b) Dichlorobis(ethylenediamine)cobalt(III) nitrate
(c) Triaquabromoplatinum (II) chloride
(d) Tetra-amminedinitroplatinum (IV) bromide
Solutions
(a) Na2[Zn(OH) 4
(b) [Coen2Cl2]NO3
(c) [Pt(H2O)3Br]Cl
(d) [Pt(NH3)4(NO 2) 2]Br2
Chapter 8 Worked Example 4
Determine the oxidation state of Mn in the
following oxides and oxoanion.
MnO MnO2 Mn2O3 Mn2O7 Mn3O4 [MnO4]-
Solutions
+2
+4
+3
+7
+2, +3
+7
MnO MnO2 Mn2O3 Mn2O7 Mn3O4 [MnO4]-
Chapter 8 Worked Example 5
Draw the structures of all possible isomers for the following
complexes. Indicate which isomers are enantiomeric pairs.
(a) Diamminebromochloroplatinum(II) (square planar)
(b) Diaquachlorotricyanocobaltate(III) ion (octahedral)
(c) Trioxalatovanadate(III) ion (octahedral)
Solutions
Br
(a)
Pt
Cl
NH3
NH3
cis
Br
Pt
NH3
NH3
Cl
t r ans
_
CN
H2O
(b)
H2O
Co
OH2
NC
CN
CN
_
NC
CN
OH2
Co
NC
NC
OH2
f ac
mer ( cis)
mer ( tr ans)
O
O
C
C
O
C
C
O
V
O
C
O
O
O
O
C
O
C
O
C
O
C
C
O
O
Two enantiomers
O
V
O
O
O
O
C
O
O
O
O
CN
Cl
Cl
(c)
C
Co
Cl
mirror
plane
O
_
OH2
Chapter 8 Worked Example 6
(a) Explain why octahedral complexes with three and eight d
electrons on the central metal atom are particularly stable.
(b) Explain under what circumstances you would expect
octahedral complexes with five or six d electrons on the central
metal atom to be particularly stable.
Solutions
(a) According to the crystal field theory, the d-electron configurations
of d3 and d8 octahedral complexes are
eg
E
t 2g
d3
(t2g)3
half-filled t2g subshell
d8
(t2g)6(eg) 2 filled t 2g subshell
and half-filled eg subshell
(b) According to the crystal field theory, the d-electron
configurations of d5 (high spin) and d6 (low spin) octahedral
complexes are
eg
E
t 2g
d5 (high spin)
(t2g)3(eg) 2 half-filled t 2g
and eg subshells
d6 (low spin)
(t2g)6 filled t2g subshell
Chapter 8 Worked Example 7
The three complex ions [Mn(CN)6]5-, [Mn(CN)6]4-, and [Mn(CN)6]3have all been synthesized and are all low-spin octahedral complexes.
For each complex ion, determine the oxidation number of Mn,
the configuration of the d-electrons (how many t2g and how many eg),
and the number of unpaired electrons.
Solution
[Mn(CN)6]5-
[Mn(CN)6]4-
Mn(CN) 6] 3-
Mn(II) (+2)
Mn(III) (+3)
eg
E
t 2g
Mn(I) (+1)
2 upaired electrons
(full configuration is
[Ar]3d54s1)
(t2g)5
1 upaired electron
(full configuration is
[Ar]3d5)
(t2g)5
2 upaired electrons
(full configuration is
[Ar]3d4)
(t2g)4
Chapter 8 Worked Example 8
Three different compounds are known to have the empirical
formula CrCl3.6H2O. When exposed to a dehydrating agent,
compound 1 (dark green) loses 2 mol water per mol of compound,
compound 2 (light green) loses 1 mol water and compound 3
(violet) loses no water.
Solution
Water of hydration is much easier to remove than
water ligands:
Compound 1 is [Cr(H2O)4Cl2]Cl.2H2O
Compound 2 is [Cr(H2O)5Cl]Cl2.H2O
Compound 3 is [Cr(H2O)6]Cl3