Exam of Selection for the Graduate in Chemistry at UFPE/Brazil - 2010.2
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Graduation Course in Chemistry
Department of Fundamental Chemistry
DQF
PG
Center of Exact and Natural Sciences
Federal University of Pernambuco – Brazil
TEL: +55 81 2126-8402 // FAX: +55 81 2126-8442
e-mail: [email protected]
SELECTION PROCESS FOR THE GRADUATION COURSES IN CHEMISTRY AT UFPE
GENERAL CHEMISTRY TEST - 28th June 2010
REGISTRATION NUMBER:
Pay attention: You must choose 5 questions. Select only one in each pair of questions to
answer (in English).
1A – Consider the earth alkaline metal (MO), where M = Mg, Ca, Sr, Ba whose melting points are 2852 0C,
2572 0C, 2430 0C and 1923 0C, respectively. Explain in detail these numbers.
1B – Explain why there exists the molecule PF5 whereas the molecule NF5 there is not?
2A – A thermodynamic investigation about DyCl3 produced the enthalpy of formation based upon the
following information
(I) DyCl3 (s) Æ DyCl3 (aq, in 4.0 M HCl )
ΔrHo = -180.06 kJ mol-1
(II) Dy (s) + 3HCl (aq, 4.0 M) Æ DyCl3 (aq, in 4.0 M HCl (aq)) + 3/2H2 (g)
ΔrHo = -699.43 kJ mol-1
(III) 1/2H2 (g) + 1/2Cl2 (g) Æ HCl (aq, 4.0 M)
ΔrHo = -158.31 kJ mol-1
Determine, with these data: a) ΔfHo (DyCl3,s);
b) Which feature on the reaction enthalpy allows you answer the item a)?
2B – For the reaction of hydrogen with iodine, the reaction constant is 2.45 x10-4 L mol-1 s-1 at 302 oC and
0.950 L mol-1 s-1 at 508 oC. a) Calculate the activation energy and the pre-exponential factor for this reaction.
b) Which is the reaction constant at 400 oC ? c) Which is the reaction order? Explain your answer.
3A – Does a precipitate of barium fluoride form when 100 mL of 1x10-3 mol L-1 Ba(NO)3 (aq) is mixed with
200 mL of 1x10-3 mol L-1 KF (aq)? Ignore possible protonation of F-. Demonstrate your answer.
3B – A sample of iron ore of mass 0.202 g was dissolved in hydrochloric acid, and the resulting solution
needed 16.7 mL of 0.0108 mol L-1 KMnO4 (aq) to reach the stoichiometric point.
Fe2+ (aq) + MnO4- (aq)
+ H+ Æ Fe3+ (aq) + Mn2+ (aq) + H2O (l)
In relation to this reaction:
(a) Balance the equation.
(b) What is the mass percentage of iron in the ore sample?
Exam of Selection for the Graduate in Chemistry at UFPE/Brazil - 2010.2
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4A – N-methylpirrolidine has a boiling point of 81oC, and piperidine has a boiling point of 106oC.
(a)
Explain this large difference (25oC) in boiling point for these two isomers.
(b)
Tetrahydropyran has a boiling point of 88oC, and cyclopentanol has a boiling point of 141oC. These
two isomers have a boiling point difference of 53oC. Explain why the two oxygen-containing isomers have a
much larger boiling point difference then the two amine isomers.
4B – Rank the following compounds in order of INCREASING heat of combustion. Briefly EXPLAIN your
answer.
5A - Use the Molecular Orbital Theory to explain:
a) Why the electron ionization of O2 increases the dissociation energy whereas for the N2 the opposite
happens.
b) Which of these molecules are paramagnetic and diamagnetic?
Molecule
O2
O2+
N2
N2+
Dissociation energy (kJ mol-1)
494
643
942
841
5B – Consider the organic molecules containing the double bond below:
H
H
C
C
H
H
ethylene
I
H
C
H
C
H
H
C
H
C
H
butadiene
II
Predicts which molecule will absorb a higher energy photon. Explain in detail your answer.
Exam of Selection for the Graduate in Chemistry at UFPE/Brazil - 2010.2
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Additional information:
Constants:
h = 6.62x10 -34 J s = 6.62x10-27erg s;
c = 3x108 m s-1 = 3x1010 cm s-1;
me = 9.1x10-31 kg = 9.1x10-28 g;
e = 1.6x10-19 C = 4.8x10-10 u.e.c.;
ε0 = 8.85x10-12 C2J-1m-1;
R = 8.31451 J K-1 mol-1 = 0.082 atm L K-1mol-1
F = 9.6485x104 C mol-1;
NA = 6.02x1023 mol-1.
Equilibrium Constant:
Ksp (BaF2) = 1.7x10-6
Atomic number:
H = 1;
Be = 4;
C = 6;
N = 7;
O = 8;
F = 9;
Mg = 12;
P=15;
Cl = 17;
K = 19;
Ca = 20;
Mn = 25;
Fe = 26;
Sr = 38;
I = 53;
Ba = 56;
Dy = 66.
Molar mass (g mol–1):
H = 1.008; Be = 9.012; C = 12.011; N = 14.007; O = 15.999;
F = 18.998; Mg = 24.305;
P = 30.974; Cl = 35.453; K = 39.098; Ca = 40.078; Mn = 54.938; Fe = 55.845; Sr = 87.62;
I = 126.904; Ba = 137.327; Dy = 162.50.
Equations:
ΔG = -nFε
ΔG = ΔG° + RT lnQ
ln k = ln A −
p=
Ea
RT
h
λ
E foton = h ν =
E foton = w 0 + E c .
Transformation relations:
1 cal = 4.184 J;
1 Å =10-10 m
RT
0 ,059
ln Q or ε = ε θ −
log Q
nF
n
1
E C = mv 2 p = mv
2
ε = εθ −
hc
λ
Exam of Selection for the Graduate in Chemistry at UFPE/Brazil - 2010.2
4/5
Graduation Course in Chemistry
Department of Fundamental Chemistry
Center of Exact and Natural Sciences
Federal University of Pernambuco – Brazil
DQF
PG
TEL: +55 81 2126-8402 // FAX: +55 81 2126-8442
e-mail: [email protected]
SELECTION PROCESS FOR THE GRADUATE COURSES IN CHEMISTRY AT UFPE
ENGLISH TEST – 28th June 2010
REGISTRATION NUMBER:
Read carefully the text in the next page and answer (in English or Portuguese) the following questions:
1 - Which example is given by the author for introducing the subject of this article?
2 – What is the effect of introducing copper and silicon atoms into NdFeB materials?
3 – Which example(s) is given by the author of nano-material applied for health?
4 – Which example(s) is given by the author of of nano-materials risk for health?
5 – What is the major message of this article?
Exam of Selection for the Graduate in Chemistry at UFPE/Brazil - 2010.2
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Afraid of the nano-world?
Mike Gibbs, Materials Today, July/August 2003, p. 64.
A senior member of the British Royal family has asked the Royal Society to investigate the dangers of
nanotechnology to society. This follows similar clarion calls in the past months. As in any field of scientific
endeavor, the arguments must be balanced and a careful distinction made between the rightful, curiositydriven endeavor of the scientist and the uptake of that endeavor in terms of technology. It is never simple. The
atom was split by scientists interested in the properties of atoms and subatomic particles. Technology turned
this into weapons of mass destruction and nuclear power; the first to be abhorred, the second to be grappled
with in terms of environmental impact and energy requirements. Any debate must be well-informed, but can
only achieve a snapshot view, as the science knowledge base is continually expanding. Care must also be
exercised in not damning a generic technology when only subsets may pose significant problems to society.
What of the nano-world? For someone like me, interested in both fundamental and applied aspects of
magnetic materials, it is relatively easy to see the impact of nanotechnology. But in fact, nanotechnology is
nothing new to those of us who have spent the last 20 years working on magnetic materials. The magnets in
your headphones or the motor in your PC disk drive or cordless power tool all depend on nanostructured
magnets. The NdFeB alloys that are used to give high efficiency at low power consumption only do so
because the magnetic grains are a few tens of nanometers in size. It is this that allows powerful magnetic
interactions, such as exchange coupling, to prevail. The head reading a computer’s hard disk comprises
magnetic and nonmagnetic layers only a few nanometers thick, where the layer thicknesses and spacing
dictate the overall magnetic properties of the structure – the ‘spin-valve’. This advance has allowed the
significant increases seen recently in data storage density for the PC market.
The subtlety of the magnetic properties of these nanomagnets is nowhere better seen than in a simple
change of composition. If we go from the archetypal Nd2Fe14B to Fe73.5Cu1Nb3Si13.5B9, we do not change the
essentials of the nanostructure, but we do move from the best hard magnetic material to the best soft magnetic
material. The science base underpinning both sets of materials is now relatively well developed, and is
certainly sufficient to see technological exploitation. Nature, in the form of magneto-tactic bacteria for
example, has used nanoscale permanent magnetic materials for navigation for as long as we can tell.
The benefits of nanomagnets in terms of greater energy efficiency in motors and drives has been
clearly established, and is allowing significant technological progress in areas where motor size and weight
for a given volume is important. In my view, this is a ‘safe’ and socially beneficial subset of nanotechnology.
The science base is not resting on its laurels. Once the significance of the nanostructure in controlling
magnetic properties was understood, scientists have been seeking ways to create nanostructures artificially.
Self-assembly is one of the core fabrication routes in many areas of nanotechnology. Recent success in
terms of hard magnets has been reported where self-assembly techniques are used to mimic the bulk alloy
synthesis used for NdFeB. This produces a new permanent magnet material with properties only 50% down
on the best NdFeB [Zeng, H., et al., Nature (2002) 420, 395]. This step has the potential to produce small
volume, synthesized magnets for a range of technologies. Thought is already being given to developing selfassembled nanomagnetic systems for smart drug delivery, tissue engineering, and image enhancement in
magnetic resonance imaging. Sensors based on nanomagnetic materials (e.g. the spinvalve) may be used in
diagnostic testing, where a given chemical is tagged magnetically and then its relative content detected in a
sample taken from a patient. This may open up the possibility of greater and cheaper testing and screening for
many diseases. If nanomagnetic technology is coupled with microelectromechanical systems, then further
opportunities arise. In Sheffield, we have already got to the proof-of-concept stage for a cochlear implant for
the profoundly deaf.
Much of the science base for these new areas remains to be developed, but it is possible to see the
potential benefits. In the medical field, we already have stringent guidelines for testing before widespread use.
We have to trust that these can adapt to these new opportunities in order to protect society. We must not stop
the progress of science, but it is always appropriate to assess any resulting technology for social or
environmental impact carefully. Above all, in the present climate, we must avoid the condemnation of all
nanotechnology as inherently dangerous, and applaud those areas from which we may safely benefit.
Mike Gibbs is professor of functional magnetic materials at the University of Sheffield and director of the Sheffield Centre for
Advanced Magnetic Materials and Devices, UK.