SECTION A
QUESTION 1 Answer all parts (This question is worth 10 marks)
(a) The colour in stained-glass windows often comes from metal
nanoparticles inside the silica glass. Archaeologists took a small sample
from an old window, and analysed it under a microscope to produce the
images shown above.
(i) Suggest what type of microscope they are using, and explain your
reasoning.
[2 marks]
(ii) Explain why the nanoparticles appear darker than their
surroundings.
[2 marks]
(iii) Suggest a technique that could be used on the metallic
nanoparticles in conjunction with the microscope, and how it would
allow identification of the metal element.
[2 marks]
(b) The glass was made predominantly from three components: quartz,
Na2CO3, and CaO.
Explain the function of each component. How would you expect the
silica in the original quartz to differ from the final glass of the window in
terms of structural order
[4 marks]
PAPER CODE CHEM313 page 3 of 11 CONTINUED
SECTION B
QUESTION 2 Answer all parts (This question is worth 30 marks)
(a) The powder X-ray diffraction data (PXRD) pattern below (l = 1.5406 )
was measured for a sample of a caesium halide compound CsX (where
X is an unknown halide ion) that adopts a cubic crystal structure.
(i) Using the ionic radii given, predict the structure types for caesium
fluoride CsF and caesium iodide CsI.
Ionic radii: Cs+ 1.88 , F- 1.33 , I- 2.20 .
[4 marks]
(ii) Sketch a 3D representation of the CsI structure, describe the
coordination of the ions and its lattice type.
[5 marks]
(iii) Using the PXRD data, calculate the lattice parameter for the
structure and determine whether the sample is CsF or CsI.
[8 marks]
QUESTION 2 CONTINUES ON THE NEXT PAGE
2q / degrees sin2 q
25.56 0.04892
29.60 0.06523
42.35 0.13046
50.12 0.17939
52.51 0.19569
61.44 0.26093
67.65 0.30985
69.65 0.32616
PAPER CODE CHEM313 page 4 of 11 CONTINUED
(b) Zeolites are microporous crystalline aluminosilicates with the general
formula Mx/n[(AlO2)x(SiO2)y]·mH2O.
(i) Explain how the structure and chemistry of zeolites enables their
use in size or shape-selective acid catalysis.
[5 marks]
(ii) Describe two methods to chemically modify the small pore Zeolite A
Na12[(AlO2)12(SiO2)12]·27H2O to tune its properties fo
r separating
long chain hydrocarbons from branched and cyclic hydrocarbons.
[8 marks]
PAPER CODE CHEM313 page 5 of 11 CONTINUED
QUESTION 3 Answer all parts (This question is worth 30 marks)
(a) A 3D representation of the crystal structure adopted by a metal sulfide
compound is shown below. Its cubic unit cell was determined to have
unit cell length of a = 5.722
(i) Describe the coordination of the ions and determine the
stoichiometry of the compound.
[4 marks]
(ii) Calculate the spacing of the (111) lattice planes d111 and the
position of the reflection in powder X-ray diffraction pattern
(l = 1.5406 ) of the compound.
[3 marks]
(iii) Identify the lattice centring of the structure shown. Using the
structure factor equation given, show that the (110) reflection is
systematically absent for the structure shown. Note: The cations
can be disregarded for this purpose.
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[6 marks]
QUESTION 3 CONTINUES ON THE NEXT PAGE
sulfide
metal cation
x
y
z
PAPER CODE CHEM313 page 6 of 11 CONTINUED
(b) Strontium titanate SrTiO3 adopts a cubic perovskite structure at 293 K.
It undergoes a structural phase transition to a tetragonal perovskite
below 100 K. Pair distribution functions (PDF) of SrTiO3 measured
above and below the transition temperature are shown below for the
Ti–O region.
(i) Sketch a 2D representation of the perovskite structure with the B
cation at the centre of the unit cell.
[2 marks]
(ii) Describe the PDF method and account for the differences observed
in the PDFs at the two temperatures.
[10 marks]
(iii) Predict whether doping SrTiO3 with Nb2O5 results in formation of a
solid doped on the A or B site, and list the possible types and
numbers of defects formed. Assume that niobium is present as Nb5+
in the structure.
[5 marks]
PAPER CODE CHEM313 page 7 of 11 CONTINUED
SECTION C
QUESTION 4 Answer all parts (This question is worth 30 marks)
(a) The probability of an electron occupying a level with energy E in the
band structure of a solid is given by the Fermi-Dirac distribution, f(E).
Define the term EF in the equation above and briefly describe its
physical meaning. Sketch graphs to show how f(E) varies with E at 0 K
and 300 K, labelling clearly EF.
( ) =
1 + exp =