Download BSc/MSci Course Unit Examination - QMplus

BSc/MSci Course Unit Examination
19 May 2014
14:30 – 17:30
CHE103 Fundamentals of Physical and Inorganic Chemistry
Duration: 3 h
YOU ARE NOT PERMITTED TO START READING THIS QUESTION PAPER UNTIL INSTRUCTED TO
DO SO BY AN INVIGILATOR.
Answer all the questions in Section A and TWO questions from Section B. The total of marks available on
the paper is 120, with Section A worth 70 marks and Section B worth 50 marks.
A detailed marking scheme is provided for you guidance.
A data booklet is also provided, which may contain data and formulae relevant to the questions on this
examination paper.
CALCULATORS ARE PERMITTED IN THIS EXAMINATION. PLEASE STATE ON YOUR ANSWER
BOOK THE NAME AND TYPE OF MACHINE USED.
COMPLETE ALL ROUGH WORKINGS IN THE ANSWER BOOK AND CROSS THROUGH ANY WORK
WHICH IS NOT TO BE ASSESSED.
IMPORTANT NOTE: THE ACADEMIC REGULATIONS STATE THAT POSSESSION OF UNAUTHORISED
MATERIAL AT ANY TIME WHEN A STUDENT IS UNDER EXAMINATION CONDITIONS IS AN
ASSESSMENT OFFENCE AND CAN LEAD TO EXPULSION FROM THE COLLEGE. PLEASE CHECK
NOW TO ENSURE YOU DO NOT HAVE ANY NOTES IN YOUR POSSESSION. IF YOU HAVE ANY
THEN PLEASE RAISE YOUR HAND AND GIVE THEM TO AN INVIGILATOR IMMEDIATELY.
PLEASE BE AWARE THAT IF YOU ARE FOUND TO HAVE HIDDEN UNAUTHORISED MATERIAL
ELSEWHERE, INCLUDING TOILETS AND CLOAKROOMS IT WILL BE TREATED AS BEING FOUND IN
YOUR POSSESSION. UNAUTHORISED MATERIAL FOUND ON YOUR MOBILE PHONE OR OTHER
ELECTRONIC DEVICE WILL BE CONSIDERED THE SAME AS BEING IN POSSESSION OF PAPER
NOTES. MOBILE PHONES CAUSING A DISRUPTION IS ALSO AN ASSESSMENT OFFENCE.
EXAM PAPERS CANNOT BE REMOVED FROM THE EXAM ROOM.
Examiners: Dr I Abrahams, Dr. S Potts, Dr S Marinakis and Dr G Chass
SECTION A
© Queen Mary University of London, 2013
Page 2 of 6
CHE103(2014)
1. Answer all parts.
(a) Briefly describe the hybridisation on the underlined atom in the following molecules.
[3 marks]
PbF2
PCl5
SF6
(b) Use VSEPR to predict the shape of each of the following molecular ions.
Molecules
(BF4)
[4 marks]
(ClO4)
(c) The radioactive decay of 238U proceeds by emission of an -particle (He nucleus) and may
be summarised as follows.
238
92
U  Az X  42 He
Calculate the values of A and Z and hence identify isotope Az X .
[2 marks]
(d) The Bohr model for the electronic structure of the hydrogen atom is based on two
assumptions. State each of these assumptions.
[4 marks]
(e) Sketch the molecular ion H3+ and briefly comment on the bonding in this ion.
[4 marks]
(f) Consider the molecules boron trifluoride (BF3) and benzene (C6H6).
(i) Sketch each of these molecules, clearly showing the principal axis of rotation. Include
the order of rotation, n, in your answer.
[2 marks]
(ii) Which of the molecules contain(s) a σh reflection plane? Include this in your sketch(es)
for part (i).
[1 mark]
(iii) Which of the molecules has the inversion symmetry element, i ?
(iv) State the point group for each of the molecules.
[1 mark]
[2 marks]
(g) A general complex can be represented as [MA2B2], where M is the metal and A and B are
the ligands.
(i) What is the coordination number of this complex?
(ii) Sketch all the possible isomers of [MA2B2].
(h) What is the systematic name for [CoCl(NH3)5]Cl2?
[1 mark]
[3 marks]
[2 marks]
Question 1 continued overleaf
(i) [Fe(OH2)6]Cl2 is a typical first-row transition metal coordination complex.
CHE103(2014)
Page 3 of 6
(i) Sketch the two other possible hydration (solvation) isomers of the complex. You can
ignore any geometric isomers that may arise.
[2 marks]
(ii) The Δo value was measured to be 10,400 cm–1 and the paring energy was determined
as 17,600 cm–1. Calculate the crystal field splitting energy for the complex. [3 marks]
(ii) What would you expect to happen to the Δo value if all six aqua ligands were replaced
by cyano ligands? Explain your answer.
[1 mark]
(j) What is meant by the term path function? Give an example.
[2 marks]
(k) Explain the terms entropy change, enthalpy change and Gibbs free energy change, and
show how they are related in an analytical form.
[4 marks]
(l) A pressurised ideal gas expands from 3.0 dm3 to 33.0 dm3 against a constant external
pressure of 2.00 atmospheres. What is the total work done on the surroundings?
[1 atm = 101325 Pa].
[3 marks]
(m) Give an expression for the equilibrium constant (Kp) for the following reaction:
[3 marks]
2 CO2(g)  2CO(g) + O2(g)
(n) An electrical current flows through a wire and does 333 J of work every second causing the
temperature of the wire to increase. After some time, the temperature of the wire stops
increasing. The current is then switched off and the wire cools. Calculate q, w and ΔU per
second at the following times:
[6 marks]
(i) Switch on.
(ii) After some time.
(iii) Switch off.
(o) For a first-order reaction in which reagent A is converted to products the integrated rate
equation is:
[A] = [A]0 ekt
(i) Derive an expression for the half-life (t1/2) of the reagent A for this reaction. [3 marks]
(ii) The isotope 90Sr emits radiation by a first-order process and has a half-life of 28.1
years. When ingested by humans it becomes incorporated permanently in bone tissue.
If 2.00 μg is absorbed at birth, how much of this isotope remains after 28.1 years. How
much remains after 281 years?
[2 marks]
(p) The Arrhenius parameters for a hydrolysis reaction are A = 5.02 × 1011 mol1dm3s1 and
Ea = 90.0 kJ mol1. Calculate the rate constant at 298 K.
[2 marks]
Question 1 continued overleaf
(q) The rate law for a reaction between A and B is of the form:
Page 4 of 6
CHE103(2014)
Rate = k [A]α [B]β
Experimental measurements for three different initial sets of reaction conditions (at fixed
temperature) have given the following data for the initial rate of reaction
(where 1 M = 1 mol dm3)
Experiment
[A] / M
[B] / M
Rate / M s-1
1
0.120
0.100
0.051
2
0.240
0.100
0.198
3
0.240
0.200
0.401
(i) Determine the values of α and β (you should assume that these values are integers).
[4 marks]
(ii) Using the data from experiment 1, and your answer to part (i), determine the units and
the value for the rate constant, k, for this reaction.
[2 marks]
(iii) Give an equation expressing the relationship between
d A 
d B
and
for the reaction
dt
dt
2A + B→ C
[2 marks]
(iv) By what factor will the rate of reaction increase if the concentration of A and B are
simultaneously tripled?
[2 marks]
SECTION B
2.
Answer all parts.
(a) State the electronic configurations of atomic B and O, clearly indicating the valence and
core electrons.
[2 marks]
(b) Make sketches showing the combinations of atomic orbitals that lead to bonding and
anti-bonding molecular orbitals in the diatomic molecules O2 and BO.
[6 marks]
(c) Using your sketches from part (b), construct molecular orbital energy level diagrams for O2
and BO. Comment on any differences in the diagrams and in each case state the molecular
electronic configuration.
[11 marks]
(d) Calculate the bond orders for O2 and BO and in each case state whether the molecule is
paramagnetic or diamagnetic.
[4 marks]
(e) State with reasoning, whether the molecule BO is likely to exist.
[2 marks]
CHE103(2014)
3.
Page 3 of 6
Answer all parts.
(a) Which of the d-block metals are not technically considered as transition metals? Explain
your answer.
[2 marks]
(b) For each of the following complexes, give the oxidation state of the metal and its d n
electron configuration.
(i) [Co(NH3)6]2+
(ii) [Cr(CO)4]4–
[2 marks]
(c) Use the crystal field approach to show how the d-orbital splitting patterns change on axial
elongation of the ligands along the hypothetical z-axis in an octahedral complex. Include
discussion of square planar complexes in your answer.
[8 marks]
(d) Account for the fact that trans-[NiCl2(en)2] has a spin-only magnetic moment of 2.83 µB
whereas trans-[NiBr2(en)2] has a magnetic moment of 0.
[3 marks]
(e) Explain what is meant by the Jahn-Teller effect, using an example to illustrate your
answer. Hint: you should refer to your answer to part (c).
[4 marks]
(f) Transition metal complexes are known for forming colourful solutions, which arise from
electronic transitions within the complex’s orbitals.
(i) State briefly what is meant by the Laporte and spin selection rules.
[2 marks]
(ii) Consider 0.1 M solutions of [Ti(OH2)6]Cl3 and K[MnO4]. Why is the solution of the
titanium complex a very pale violet in comparison to the intense purple colour of the
manganese complex?
[4 marks]
4.
Answer all parts.
(a) A large kettle operates at 1000 W and holds 5400 g of water when full. The temperature of
tap water in spring is 10°C. Assume the water to be pure H2O with the following
properties: molar mass = 18 g mol1; CP = 4.2 J mol1 K1; ΔvapH = 41 kJ mol1 (at 100°C).
(i) How long would the kettle take to boil if filled with tap water?
[6 marks]
(ii) How long would the kettle take to boil to dry (all water evaporated)?
[6 marks]
(b) Phosgene gas is formed at 298 K according to the following reaction.
CO(g) + Cl2(g)  COCl2(g)
Calculate G and provide an expression for the equilibrium constant for this reaction. fG
[7 marks]
of CO(g) and COCl2(g) are –137 and 210 kJ mol–1, respectively.
(c) Determine the entropy difference between solid and liquid states for a substance melting at
100°C and having a heat of fusion of 10 kJ mol–1.
[5 marks]
5.
The following mechanism is proposed for the destruction of ozone in the upper atmosphere
Page 6 of 6
CHE103(2014)
O3
→
O2 + O
k1
O2 + O
→
O3
k2
O + O3
→
2 O2
k3
(a) Write down an equation for d[O3]/dt.
[3 marks]
(b) Write down an equation for d[O2]/dt.
[3 marks]
(c) Write down an equation for d[O]/dt.
[3 marks]
(d) In the context of consecutive elementary reactions, explain what is meant by the following:
(i) pre-equilibrium,
[2 marks]
(ii) the steady state approximation.
[2 marks]
(e) To which of these three species (O, O2, O3) would it be appropriate to apply the steady
state approximation? Give your reasons.
[3 marks]
(f) By applying the steady state approximation to your chosen species, derive a rate equation
for this reaction (i.e. an equation relating d[O3]/dt to [O3] and [O2]). Simplify your answer
as much as possible.
[9 marks]
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End of Paper