UNIVERSITY COLLEGE LONDON




EXAMINATION FOR INTERNAL STUDENTS



MODULE CODE : CHEM0014

ASSESSMENT : CHEM0014C5UC/ CHEM0014A5UD
PATTERN

MODULE NAME : CHEM0014 - Inorganic Chemistry

LEVEL: : Undergraduate

DATE : 12-May-2022

TIME : 10:00

Controlled Condition Exam: 4 Hours exam

You cannot submit your work after the date and time shown on
AssessmentUCL – you must ensure to allow sufficient time to upload and
hand in your work

This paper is suitable for candidates who attended classes for this
module in the following academic year(s):

Year
2020/21 and 2021/22

Additional material

Periodic table.pdf, Physical constants.pdf and Character tables.pdf
Special instructions

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Exam paper word
count
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TURN OVER
CHEM0014 page 2 of 7

Candidates should attempt ALL questions. The numbers in square brackets in the right-
hand margin indicate the provisional allocation of marks to the subsections of a
question.

1. Answer ALL parts.
(a) The Latimer diagram for ruthenium species in acidic solution (pH = 1) is
shown below.


(i) Calculate the reduction potential for the non-adjacent couple, X. [2]
(ii) Construct a Frost diagram for ruthenium in acidic solution. [4]
(iii) Identify which ruthenium species are unstable with respect to
disproportionation in acidic solution. Justify your answer(s). [2]
(iv) Which ruthenium species is the strongest oxidizing agent in acidic
solution, and which is the strongest reducing agent? [2]
(v) Consider the stability field of water. At pH = 1 which ruthenium
species can kinetically and/or thermodynamically oxidize water? [2]
(vi) A Frost diagram for the first-row transition metals (M) in acidic
solution (pH = 1) is shown below. What would happen if excess
RuO4– (aq) was added to an acidic solution that contained (where
applicable) an M2+ ion? [3]

(This diagram by Stephen Contakes is licensed under a Creative Commons Attribution 4.0 International License)

[Question 1 continued overleaf
RuO4 RuO4
– RuO2
2+
1.00 V 1.60 V 1.50 V
Ru(OH)2
2+ Ru3+ Ru2+
0.86 V 0.25 V 0.46 V
Ru
X
CHEM0014 page 3 of 7

Question 1 continued]
(b) Account for each of the following:
(i) The dissolution of La(NO3)3 in water forms an acidic solution. [2]
(ii) In aqueous solution the formation constant (log10 K1) of 18-crown-6
with Li+ is 1.5 but with K+ is 6.0. [2]
(iii) The solubilities of LiF and LiI in water at 25 °C are respectively
0.125 g and 167 g per 100 g water. [2]
(iv) Li+ has a stronger interaction with OH– than with SR–. [2]
(v) For the successive formation constants of aqueous Cd2+ with Br
–
,
K4 is larger than K3 (log10 K1= 1.56, log10 K2= 0.54, log10 K3= 0.06,
log10 K4= 0.37). [2]


CHEM0014 page 4 of 7

2. Answer ALL Parts.
(a) Derive molecular orbital diagrams for both H2O and H2S (C2v), positioning
the molecule in the yz plane. Make reference to symmetry, spatial
overlaps and energy differences, and display both diagrams on a single
figure to allow a direct comparison of orbital energies between molecules. [20]
(b) Predict the relative ligand character (-donor, -donor, -acceptor) of H2S
as a ligand in a transition metal complex as compared to H2O (assuming
equivalent stable complexes could be formed). Justify your answer by
reference to energy levels in your diagram from part (a) and by making
explicit reference to the partial calculation outputs from WebMO shown
below. [5]

Calculated values for H2O
Orbital symmetries:
Occupied (A1) (A1) (B2) (A1) (B1)
Virtual (A1) (B2)

Molecular Orbital Coefficients:
MO number: 1 2 3 4 5
Symmetry (A1)--O (A1)--O (B2)--O (A1)--O (B1)--O
Energy (Ha) -- -20.24708 -1.22175 -0.57802 -0.42996 -0.38346

MO number: 6 7
Symmetry (A1)--V (B2)--V
Energy (Ha) -- 0.50820 0.65327

Calculated values for H2S
Orbital symmetries:
Occupied (A1) (A1) (B2) (A1) (B1) (A1) (B2) (A1) (B1)
Virtual (A1) (B2)

Molecular Orbital Coefficients:
MO number: 1 2 3 4 5
Symmetry (A1)--O (A1)--O (B2)--O (A1)--O (B1)--O
Energy (Ha) -- -90.73392 -8.63804 -6.27117 -6.26799 -6.26522

MO number: 6 7 8 9 10
Symmetry (A1)--O (B2)--O (A1)--O (B1)--O (A1)—-V
Energy (Ha) -- -0.88779 -0.53190 -0.35956 -0.27276 0.46684

MO number: 11
Symmetry (B2)—V
Energy (Ha) -- 0.52763




CHEM0014 page 5 of 7

3. Answer ALL parts.
(a) Consider the following list of species:
PH3, CH3OH, NEt3, Br
–
, CN
–
, ⋅CH3, CH3SH
Classify their ligand character (-donor, -donor, -acceptor) in the
context of ligand field theory, and arrange them in order from weak field to
strong field (spectrochemical series). [5]
(b) For each of the following pairs of complexes, indicate which has higher
ligand field stabilization energy (LFSE) and BRIEFLY explain why.
[Fe(CN)6]3– vs [Fe(CN)6]4–
[Cr(H2O)6]3+ vs [Fe(H2O)6]3+
[Fe(CN)6]4– vs [Ru(CN)6]4– [6]
(c) With the use of d-level diagrams, explain why [NiCl4]2– is paramagnetic
whilst [PdCl4]2– and [PtCl4]2– are diamagnetic. [4]
(d) Mo(II) and Cu(II) ions form dimeric acetato complexes of composition
M2(OAc)4, in which the local environment of each metal ion is square
planar (illustrated for Mo below). Using appropriate d-level diagrams,
indicate the electronic configuration of Mo(II) and Cu(II) in these
complexes. Discuss any metal-metal bonding resulting from the interaction
of the d-levels on the metal atoms. Show that your solution is consistent
with equilibrium M-M distances of 2.079 Å for the Mo(II) dimer and 2.616 Å
for the Cu(II) dimer. [10]




CHEM0014 page 6 of 7

4. A PXRD pattern of a sample of a polymorph of titanium dioxide is shown below.
The pattern was obtained using Mo Kα1 X-ray radiation (λ = 0.7093 Å).

(a) The peak labelled A can be indexed as a 220 reflection and the peak
labelled B can be indexed as 211. Assuming a tetragonal lattice, use
these two peaks to estimate the lattice parameters for this polymorph of
titanium dioxide. [6]
(b) This polymorph of TiO2 crystallizes in a centrosymmetric space group
which has the following symmetry operators:
x, y, z; −x, −y, z; y, x, z; −y, −x, z;
½−x, ½+y, ½+z; ½+x, ½−y, ½+z; ½−y, ½+x, ½+z; ½+y, ½−x, ½+z;
plus a further 8 symmetry operators related to the above by an inversion
centre at the origin. The atomic coordinates for Ti are (0,0,0) and for O
are (0.305,0.305,0).
(i) List the positions of all of the atoms within the unit cell and hence
determine the number of formula units per unit cell. [3]
(ii) Determine the density in g cm−3 for this polymorph of TiO2. [2]
(iii) Calculate a Ti—O bond length. [1]

[Question 4 continued overleaf
CHEM0014 page 7 of 7

Question 4 continued]
(c) Assuming zero atomic vibrations, derive a simplified expression for the
structure factors Fhkl for this material. Comment on the intensities of the
001 and 102 reflections. [7]
(d) (i) Determine the Hanawalt index for this material. [4]
(ii) Briefly discuss how the purity of the sample might be assessed
from the PDF entry for this material in the ICDD database. [2]




END OF PAPER