UNIVERSITY OF KWAZULU-NATAL
SCHOOL OF CHEMISTRY (Pietermaritzburg)
MAIN EXAMINATIONS: JUNE 2015
SUBJECT, COURSE, & CODE:
Chemistry, Inorganic Chemistry II, CHEM210
TOTAL MARKS: 100
DURATION 3 HOURS
Internal Examining Authority: Dr. S. Ojwach, Prof. H. Friedrich
Internal Examiners: Dr. I.N. Booysen, Dr. M. P. Akerman, and Prof. O. Q. Munro
STUDENTS ARE REQUESTED, IN THEIR OWN INTERESTS, TO WRITE LEGIBLY
NOTES:



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This paper consists of 9 pages (including a Periodic Table and Data
Sheet). Please ensure that you have them all.
The use of non-programmable electronic calculators is permitted.
Use the mark allocation of each question as a guide to the depth of
answer required.
Pencil may only be used for drawings.
Answer ALL questions.
QUESTION 1
(a)
Explain the difference between cubic and hexagonal close packing arrangements.
(2)
(b)
Tungsten (W) exhibits a body-centred (bcc) unit cell structure.
(i)
Draw the bcc unit cell and determine the number of atoms in the unit cell.
(2)
(ii)
Calculate the density of tungsten (W) in g cm–3 with the aid of the data below.
Show your calculations clearly.
Avogadro’s number = 6.022 x 1023 mol–1
Relative atomic mass for W = 183.85 g mol–1
Radius for W = 1.37 Å (1 Å = 10–8 cm)
(4)
(iii)
Calculate the packing efficiency of the unit cell of tungsten.
(5)
[13]
Page 1 of 9
EXAMINATIONS: JUNE 2015
UNIVERSITY OF KWAZULU-NATAL, PIETERMARITZBURG: School of Chemistry
COURSE, SUBJECT, & CODE: Chemistry, Inorganic Chemistry, CHEM210
QUESTION 2
(a)
Use the Pauling method to estimate the ionic radii of Cs+ and I–, given that CsI has a
unit cell edge length of 4.56 Å. Hint: The shielding constant for ions with a Xenon
configuration is 45.75.
(2)
(b)
Explain why it is impossible for lithium oxide not to have the zinc blende structure.
(2)
(c)
NaCl has a ccp arrangement of its anions with all the cations occupying the octahedral
sites.
(i)
Using a labelled diagram for illustrative purposes, calculate
𝑟+
𝑟−
for a perfect fit
of cations in the octahedral sites (r+ = radius of cation; r – = radius of anion).
(2)
(ii)
How does the idealised value compare with the actual
𝑟+
𝑟−
for NaCl?
[r(Na+) = 0.96 Å; r(Cl–) = 1.81 Å.]
(2)
(d)
Lithium hydride (LiH) has the sodium chloride crystal structure with a unit cell edge
length, a, of 4.08 Å (1 Å = 10–10 m). Calculate the electron attachment enthalpy for
the formation of the hydride ion, i.e., the enthalpy change for the process:
H(g) + e– → H–(g)
Additional data required are:
Madelung constant for NaCl: 1.747
Avogadro’s number: 6.022  1023 mol–1
Charge on an electron, e: 1.602  10–19 C
Vacuum permittivity, εo: 8.854  10–12 C2 m–1 J–1
Born exponent for LiH(s): 5.0
ΔHof for LiH(s): –141 kJ mol–1
ΔHovap for Li(s): +159 kJ mol–1
ΔHodiss for H2(g): +434 kJ mol–1
ΔHoion for Li(g): +520 kJ mol–1
(7)
[15]
Page 2 of 9
EXAMINATIONS: JUNE 2015
UNIVERSITY OF KWAZULU-NATAL, PIETERMARITZBURG: School of Chemistry
COURSE, SUBJECT, & CODE: Chemistry, Inorganic Chemistry, CHEM210
QUESTION 3
(a)
Consider the following neutral six-coordinate complex, compound 1, and answer the
questions which follow.
compound 1
(i)
Name the ligands coordinated to the metal ion.
(1.5)
(ii)
Give the denticity of each type of ligand coordinated to the metal ion.
(1.5)
(iii)
What is the oxidation state of the metal ion?
(1)
(iv)
(b)
Reaction of 1.0 mol of compound 1 with 1.0 mol of Ag(CN) leads to the
formation of a new complex, compound 2, and 1.0 mol of AgCl(s). Write a
balanced chemical equation to represent this reaction using condensed
structural formulae with the correct abbreviations for the ligands.
(2)
Consider the structure of compound 3 below, which has the abbreviated formula
CoBr2(pn)2 (where pn = 1,3-diaminopropane).
compound 3
(i)
Draw the enantiomer of compound 3 and label the isomer as  or .
(2)
(ii)
With reference to compound 3, explain the term “enantiomers” and how
enantiomers exhibit different physical properties, e.g. behave in polarized
light.
(2)
Page 3 of 9
EXAMINATIONS: JUNE 2015
UNIVERSITY OF KWAZULU-NATAL, PIETERMARITZBURG: School of Chemistry
COURSE, SUBJECT, & CODE: Chemistry, Inorganic Chemistry, CHEM210
(iii)
Both bromide ions of compound 3 may be substituted (replaced) by
thiocyanate ions (SCN–) to give compound 4. Draw all possible linkage isomers
for compound 4. (Note: The stereochemistry of the two chelate rings above
does not change when the bromide ions are replaced.)
(4)
[14]
QUESTION 4
(a)
Consider the two hexadentate ligands below. The tabulated data are for the formation
of the [Zn(L)]2– complex at a temperature of 298 K in each case. (Given: gas constant,
R = 8.314 J K–1 mol–1.)
EDTA4
log K1
TMDTA4
[Zn(EDTA)]2–
[Zn(TMDTA)]2–
16.49
15.27
G (kJ mol–1)
H (kJ mol–1)
S (J K–1 mol–1)
(i)
–87.1
–20.5
–9.60
247
260
Using the values of H and S from the table above, and showing all working,
calculate the value of G for [Zn(EDTA)]2– and then show that the value of log
K1 is 16.49.
(4)
(ii)
Briefly explain why the value of log K1 for [Zn(TMDTA)]2– is smaller than the
value of log K1 for [Zn(EDTA)]2–. Insightful and correct analysis in terms of the
thermodynamic data and ligand structures will earn full credit.
(3)
(iii)
List two commercial uses for the ligand EDTA4–.
(1)
Page 4 of 9
EXAMINATIONS: JUNE 2015
UNIVERSITY OF KWAZULU-NATAL, PIETERMARITZBURG: School of Chemistry
COURSE, SUBJECT, & CODE: Chemistry, Inorganic Chemistry, CHEM210
(b)
Consider the structure of the ligand H3NTA shown below.
H3NTA
(i)
How many donor atoms does the ionized (deprotonated) ligand NTA3– have?
(1)
(ii)
H3NTA reacts with FeCl3 in aqueous solution according to the following
stoichiometry:
H3NTA + FeCl3 ⇄ [Fe(NTA)Cl2]2– + HCl + 2 H+
Sketch the structure of the metal complex [Fe(NTA)Cl2]2– formed in this
reaction.
(2)
(c)
Arrange the following complexes in order of increasing stability (log K1) under
identical conditions. Explain your order clearly.
A
B
C
(3)
[14]
QUESTION 5
Sulphur monoxide, like carbon monoxide, exists as a gas, SO(g), and is a well-known ligand
for some metal ions.
(a)
Construct a suitable molecular orbital (MO) energy level diagram to account for the
bonding in sulphur monoxide (SO). Label all orbitals and include all electrons.
(5)
(b)
Explain whether the SO molecule is paramagnetic or diamagnetic and calculate the S–
O bond order for this compound.
(2)
Page 5 of 9
EXAMINATIONS: JUNE 2015
UNIVERSITY OF KWAZULU-NATAL, PIETERMARITZBURG: School of Chemistry
COURSE, SUBJECT, & CODE: Chemistry, Inorganic Chemistry, CHEM210
(c)
Sketch an atomic orbital overlap diagram to show how the SO p MO is formed and
write a simple wave function equation to describe this MO using the proper notation.
(2)
(d)
When sulphur monoxide binds to a metal ion, it is possible for the M II–(SO) adduct to
undergo an internal redox reaction that converts neutral SO to a bound SO– ion:
MII–(SO)
⇄
MIII –(SO)–
What is the expected bond order of the SO– ion? Comment on the likely reactivity of
the SO– ion taking into account its electronic structure.
(2)
[11]
QUESTION 6
(a)
(b)
The following questions relate to effective nuclear charge:
(i)
What is the trend in the variation of effective nuclear charge from left to right
across a period of the Periodic Table?
(1)
(ii)
What is the cause of the variation in the effective nuclear charge across a
Period?
(2)
(iii)
Explain how this variation in effective nuclear charge impacts on the atomic
radius of the period two elements.
(1)
Given below are the successive ionization energies of a Period two element:
Ionization
energy
(kJ mol–1)
First
Second
Third
Fourth
Fifth
Sixth
1090
2350
4610
6220
37800
47000
This data most likely corresponds to which element? Clearly explain your reasoning.
(3)
Page 6 of 9
EXAMINATIONS: JUNE 2015
UNIVERSITY OF KWAZULU-NATAL, PIETERMARITZBURG: School of Chemistry
COURSE, SUBJECT, & CODE: Chemistry, Inorganic Chemistry, CHEM210
(c)
The following questions relate to catenation and the Group 14 elements:
(i)
What is catenation?
(1)
The bond enthalpies for the group 14 elements are summarised below:
C–C
Si–Si
Ge–Ge
(ii)
348 kJ mol–1
326 kJ mol–1
186 kJ mol–1
What is the cause of the large variation in bond enthalpy?
(2)
(iii)
Using the above data explain the trend in the likelihood of catenation for these
elements.
(2)
(d)
The chemistry of carbon and silicon vary significantly. An example of this difference is
the structures of CO2 (which is a gas) and SiO2 (which is a solid). Explain why these two
seemingly similar compounds have different chemistries.
(2)
(e)
Discuss the variation in stability of the +2 and +4 oxidation states of tin and lead. Your
answer should include a full explanation of why there is a difference in stability.
(4)
[18]
QUESTION 7
(a)
The following questions relate to “syn-gas”:
(i)
What is syn-gas?
(1)
(ii)
Give an equation for the preparation of syn-gas on an industrial scale?
(1)
(iii)
(b)
How is the unwanted component of syn-gas removed? Include relevant
reaction equations.
(2)
The following questions relate to lithium aluminium hydride:
(i)
Give the reaction equation for the synthesis of lithium aluminium hydride.
(1)
Page 7 of 9
EXAMINATIONS: JUNE 2015
UNIVERSITY OF KWAZULU-NATAL, PIETERMARITZBURG: School of Chemistry
COURSE, SUBJECT, & CODE: Chemistry, Inorganic Chemistry, CHEM210
(ii)
Give a reaction equation to illustrate that lithium aluminium hydride can be
used to reduce inorganic compounds such as boron trichloride to the
corresponding covalent hydrides.
(1)
(c)
Vanadium(II) hydride (VH2) is a candidate for hydrogen storage in fuel cells. If the
density of VH2 is 5.8 g cm–3, what is the density of hydrogen in this storage medium?
If liquid hydrogen has a density of 0.071 g cm–3, comment on the suitability of
vanadium hydride as a hydrogen storage medium.
(3)
(d)
Metallic hydrides can be described as “non-stoichiometric”.
(i)
What is meant by “non-stoichiometric”?
(1)
(ii)
How is it possible for metallic hydrides to be non-stoichiometric?
(2)
(iii)
(e)
Give two examples of metallic hydrides.
(1)
Plot a sketch graph of boiling point versus molecular mass for the Group 15 hydrides
and comment on the shape of the curve.
(2)
[15]
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Page 8 of 9
EXAMINATIONS: JUNE 2015
UNIVERSITY OF KWAZULU-NATAL, PIETERMARITZBURG: School of Chemistry
COURSE, SUBJECT, & CODE: Chemistry, Inorganic Chemistry, CHEM210
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