CAMBRIDGE INTERNATIONAL AS & A LEVEL CHEMISTRY: COURSEBOOK
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Coursebook answers
Chapter 24
Self-assessment questions
1
a
i
Ti 1s2 2s2 2p6 3s2 3p6 3d2 4s2
ii
Cr 1s 2s 2p 3s 3p 3d 4s
iii
Co 1s2 2s2 2p6 3s2 3p6 3d7 4s2
iv
Fe3+ 1s2 2s2 2p6 3s2 3p6 3d5 4s0
v
Ni2+ 1s2 2s2 2p6 3s2 3p6 3d8 4s0
vi
Cu+ 1s22s2 2p6 3s2 3p6 3d10 4s0
b
2
6
2
6
5
1
For scandium the only observed
oxidation state is +3, so the electronic
configuration of Sc3+ is 1s2 2s2 2p6 3s2
3p6 4s0. This ion has no d electrons,
so does not satisfy the definition of
a transition element. The only ion
of zinc is Zn2+, with the electronic
configuration 1s2 2s2 2p6 3s2 3p6 3d10
4s0. This ion has a completely filled,
not a partially filled, d subshell − so
zinc is not a transition element.
c
The + 7 oxidation state involves all of
the 3d and 4s electrons in manganese.
d
Oxidation state of vanadium in a =
(VO2+) = +5; b (VO2+) = +4;
c (V3+) = +3; d (V2+) = +2.
e
i
ii
2
2
a
+4 as this involves all the 4d and
5s electrons, leaving the noble gas
electronic configuration of krypton.
The positive value indicates that the
reaction as written is feasible and its
relatively large value suggests that the
reaction is likely to occur (although
values of E⦵ tell us nothing about the
rate of a reaction).
d
6
e
i
0.0153 × 0.001 = 0.000 015 3 mol
ii
0.000 015 3 × 6 = 0.000 091 8 mol
iii
i
+3
ii
+2
iii
+3
iv
+3
v
+2
3
4
a
[Ni(EDTA)]2−
c
ethanedioate ion (ox) and
ethane-1,2-diamine (en)
a
i
ii
H2N
Cl
NH2
Co
Fe2+(aq) → Fe3+(aq) + e−
6Fe2+(aq) → 6Fe3+(aq) + 6e−
+
H2N
−
Cr2O72−(aq) + 6Fe2+(aq) + 14H+(aq) →
2Cr3+(aq) + 6Fe3+ + 7H2O(l)
E⦵ = +1.33 V + (−0.77 V) = +0.56 V
NH2
Cl
iii
Cr2O7 (aq) + 14H (aq) + 6e →
2Cr3+(aq) + 7H2O(l)
c
6
ZrO2
2−
= 0.003 67 mol dm−3
b
Cr2O72−(aq) + 14H+(aq) + 6e− →
2Cr3+(aq) + 7H2O(l)
b
0.000 0918
0.025
b
i
They are mirror images, which are
not superimposable.
NC
Cl
NC
Ni
Ni
Cl
cis-isomer
1
2–
2–
Cl
NC
Cl
CN
trans-isomer
Cambridge International AS & A Level Chemistry © Cambridge University Press 2020
CAMBRIDGE INTERNATIONAL AS & A LEVEL CHEMISTRY: COURSEBOOK
ii
5
Non-polar, as the charge
is distributed perfectly
symmetrically around the central
nickel (with both cyanide ligands
diagonally opposite each other in
the square planar structure, and
similarly with the two chloride ions).
a
+2
b
[CoCl4]2−(aq) + 6H2O(l) →
[Co(H2O)6]2+(aq) + 4Cl−(aq)
c
A
[ PtCl (NH ) (aq)] Cl (aq) 
[ PtCl ] (aq)  [ NH (aq) ]


−
6
a
i
ii
iii
b
i
2
2
4
Ni2+ ...3d8
d
Sc3+ ions have electronic configuration
[Ar]3d04s0. If d-orbital splitting were
to occur in a complex ion containing
Sc3+, there would be no electrons in
the three 3d orbitals of lower energy,
so visible light would not be absorbed
in promoting an electron from a lower
energy 3d orbital to a higher energy
3d orbital.
e
Zn2+ ions have electronic configuration
[Ar]3d104s0. If d-orbital splitting were
to occur in a complex ion containing
Zn2+, each of the 3d orbitals would
contain two electrons, and would
therefore be fully occupied. Visible
light could not be absorbed in
promoting an electron from a lower
energy 3d orbital to a higher energy 3d
orbital.
3
 Ni ( NH3 )4 ( H2O )2  (aq)
 Ni ( H2O ) 2+ (aq)   NH3 ( aq )  4
6


2+
[Fe(H2O)6]3+(aq)]:
H2O
H2O
OH2
Fe
H2O
OH2
H2O
2
3d
 Cr ( H O ) Cl + (aq) 
2
2
4
 

3+
 Cr ( H O )  (aq)  Cl – ( aq ) 2
2

6
 
 
ii
SCN− has a higher value of Kstab
than H2O. So the position of
equilibrium is shifted to the right.
iii
[Fe(H2O)5SCN]2+(aq)
iv
Yes; a colour change is likely /
possible. F− has a higher value
of Kstab than SCN−. So F
substitutes for SCN (and for
water) because the position of
equilibrium is shifted to the right.
7
c
2
3 2
2−
electron from one of the three lower
non-degenerate orbitals absorbs that
amount of energy (ΔE) and jumps into
one of the two higher non-degenerate
orbitals. This leaves the transmitted
light coloured.
a
orbitals at the same energy level
b
The ligands in a complex cause
the d orbitals to split, forming two
sets of non-degenerate orbitals.
The difference in the energy (ΔE)
between the non-degenerate d orbitals
corresponds to the energy of part
of the visible spectrum of light. So
when light travels through a solution
or a solid containing the complex, an
Cambridge International AS & A Level Chemistry © Cambridge University Press 2020