CS MAIN 2015 CHEMISTRY (PAPER-I)

1 · The wave functions for a particle in a one-dimensional box (length are

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The van der Waals equation for real gases is given by

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where Pobs is the observed pressure, V is the volume, n is the number of moles, R is the· gas constant and T is the temperature. a and b are constants
characteristic of a gas.

Is Pobs greater or less than the pressure expected for an ideal gas? Wnte a few sentences outlining the:"reason(s) for your answer.10

Consider the halogens Cl2(g) and Br2(g).
Rank these in order of increasing a. Justify your answer.
Rank these in order of increasing b. Justify your ranking.

The standard enthalpy of vapourization, Mi", for water at 100 DC is around 30· 0 kJ mol-l and 1'mol of liquid water is undergoing vapourization at 100 DC and, 1 atm pressure.

Calculate w.
Calculate tou.
(iii) Under these conditions does the entropy change of the system or the surroundings drive the process? State reasons for your answer. 10

Buckminsterfullerene molecules crystalllize to form a face-centred cubic unit cell of C60 molecules.
How many buckminsterfullerene molecules are there in the unit cell of buckminsterfullerene?
How many carbon atoms are there in the unit cell?
What is the mass of carbon atoms in the unit cell?
(ill) Given' that the radius of a buckminsterfullerene molecule is 502 pm. Calculate the'density of buckminsterfullerene in kg m

Construct the MO diagram for the CO molecule. On the basis of the diagram, state whether the bonding in metal carbonyls is of the type M-C or M-O.Explain your reasoning. You may ignore the Is electrons. 10

2. The Bohr model for single-electron atoms predicts that the energies of the allowed orbits are given by

En =-2·18xlO-lB Z2 /n2 joule

where n 00 and Z is the nuclear charge.

The Balmer series corresponds to transitions between which energy levels in the hydrogen atom? Does the Paschen series appear at higher or lower wavelengths than the Balmer series?

Calculate the minimum energy (in required to ionize an electron in the n 2 state of hydrogen atom.

Calculate the wavelength (in nm) of the ,photon emitted by, an electron in
making the transition from the n 3 to n 1 level of the singfe-electron ion, Li

Is the photon higher in energy or lower in energy than the transition from n=3 to n=l in'Be3 Explain your answer.

In terms of the kinetic molecular model of matter, explain why-
a liquid in an open container will eventually vapourize even if the temperature is below the boiling point;
the temperature of a pure, boiling liquid substance does not change even though heat is continually flowing into the container. 5+5

How high will a liquid rise in a capillary tube of O· I mm diameter, if its density is I· 3 X 103 kg m and surface tension 0·065 Nm Assume O(Theeta) O.

Copper metal has an f.c.c. unit cell. The accepted value for the metallic radius of copper is 0·128 nm. Calculate the density of copper (at. wt. ofCu 63·5).

3. A bomb calorimeter has a measured heat capacity of 6·27 kJ/C. The combustion of I· 84 g of magnesium wt. 24· 3 g mol-I) leads to a temperature change from 21· 30 ·C to 25·56 ·C. The specific heat of water is 4·18J/'C/g.

Calculate the change in internal energy per mole of Mg for the reaction

Mg 1/2 02 MgO

If the reaction were carried out open to the atmosphere at 25 ·C, what would be the enthalpy change of the reaction per mole of Mg? 10

An important metabolic step is the conversion of fumarate to malate
Fumarate ... Malate
Fumarate ... Malate
At 25 the equilibrium constant for the reaction,.K =am at where at is the activity of fumarate and am is the activity of malate.

Calculate the standard Gibbs energy change, "AG", for the above reaction.
Calculate the reaction Gibbs energy, "'AGr when at some time during the course of the reaction, the reaction quotient, is 0·01.
What is the difference in chemical potential between the two species when Q=O·OI? .

Benzene and toluene fonn a nearly ideal solution. At 80oC. the vapour pressure of pure benzene (MW 78·i) is 753 torr and that of pure toluene (MW 92.1) is 290 torr. The following questions refer to a solution containing equal massesJof benzene and toluene

Calculate the partial pressure of each substance in the vapour that would be in equilibrium with the above solution at 80 ·C.
At what atmospheric pressure will the solution boil at 8O·C?
Suppose that some of the vapour from the solution is collected and condensed. What will be the composition of the resulting liquid?

The viscosity of gases increases with temperature, but the viscosity of liquids decreases with temperature. Explain, 10

4. The BF molecule is isoelectronic with CO.

Construct an MO diagram for the BF molecule. What assumptions can be made in BF which make the MO construction for this molecule much more straightforward than for CO?
Discuss the similarities and differences in the electronic structures of BF and CO in terms of cr and 1t bonding and non-bonding orbitals. What possible Lewis structures can be drawn for BF and CO, and which of these is most reasonable for each species based on your diagram? 10+10

Sodium lauryl sulphate can decrease the surface tension of water, but sodium chloride increases the surface tension. Explain. 5

On gradual increase of surfactant from zero concentration to a higher value, there is a sharp change in surface tension after some value. What is
the reason for this? 5

The phase diagram for a pure substance is shown below. Use the diagram to answer the following questions

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What does the point V represent? What characteristics are specific to the system only at point
What does each point on the curve between V and Wrepresent?
(iii) Describe the changes that the system undergoes as the temperature slowly increases from X to Y to Z at atm.
In a solid-liquid mixture of the substance will the -solid float or sink? Explain.


B I SECTION-B

5. Discuss, with the aid of.diagrams-

why a block of magnesium is attached to a pipeline to reduce corrosion;
what is meant by pitting corrosion and how it occurs. 10 .
Explain why

is essentially colourless, while is highly coloured;
examples_of carbonylate anions are more than those of metal carbonyl cations. 5+5

Why do lanthanoid ions have similar chemical properties even with variation of atomic number and have higher lifetime in excited states than transition metal ions? 10

Why is Ca2+ more suitable than Mg2+ for fast signalling process in cells? 5

Which metal ions are responsible for decomposition of H20 to 02 during photosynthesis by plants, and what is the nature of this ionic cluster and its ionic state? 5

In an experiment to measure the quantum efficiency of a photochemical reaction, the absorbing substance was exposed to 490 nm light from a 100 W source for 45 minutes. The intensity of the transmitted light was 40% of the intensity of the incident light. As a result of irradiation, 0'344 mol of the absorbing substance decomposed. Find the quantum efficiency. 10

6. Photodimerization of a monomer M in the presence of a photoinitiator occurs by a chain polymerization process in three steps

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where kp and kt are the rate constants for the propagation and termination steps, involving the propagating chain radical and labs is the intensity of
absorbed light. Show that the rate of photopolymerization (i.e., the rate of loss of monomer) is proportional to the square root of the light intensity.


The adsorptipn of a surfactant on colloidal Zr02 suspended in water followed a Langmuir isotherm with the results .shown below

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Given that 10 g of Zr02 colloid was used in the experiment and that the cross-sectional area of a single .surfactant molecul is 0·25 nm2 /molecule.
Calculate the surface area of the Zr02 in. units of M2g -l.

Chlorine trifluoride, ClF3" is one of the most reactive compounds known. It can be made by heating Cl2 and F2 in a closed container.

Draw the electron-dot structure of ClF3.

What is the electron-pair geometry for ClF3?

Knowing that the molecule is polar, what can you conclude about the molecular geometry?

Calculate the standard enthalpy of formation of gaseous ClF3' given the following bond energies

F-F 159 kJ mol-1
Cl-Cl 243 kJ mol-1
Cl-F 255 kJ mol-1



7. For the galvanic cell

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the standard reduction potentials at 25 ·C are the following

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Write down the two spontaneous half-cell reactions based on the convention for electron flow for the cell as written.
Calculate the e.m.f. of this cell based on the concentrations given. In your calculations, use the fact that the mean activity coefficients for Zn2+
and Cu2+ ions under the conditions given are 0·3 and 0·2, respectively. 10


The hydrolysis of bicarbonate ions in water at a high pH

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follows the rate law

Rate k [HC03]

where k 0·01 s-I at 25

What is the overall order of the reaction?
What is the half-life of HC03, if the initial concentration of HC03 [HC03]o =0·001 M
(iii) Is hydroxide ion a catalyst in this reaction? Explain in two lines.
Write down the Arrhenius eqliation and define each of the terms in this equation. What each term physically relates to?
What is the rate constant of the above equation at 350 if the activation energy of the reaction is 10·0 kJ mol-I?
The hydrolysis reaction is exothermic. Draw a curve of the reaction showing how the energy of the system changes in going from reactants to products. Mark in the activation energy for the forward and back activation steps, and show the"overall change in energy of the reaction.

Arrange the following ligands in order of increasing A. and justify your arrangement: 5

NH3 NF3 and NCl3

The complex is less paramagnetic than . Explain. 5

8. Account for the following observations

Although NH-CH-cH2-NH2 has three basic sites,
I
NH2
it functions as a bidentate ligand when the ligand is in excess.

Copper(I) iodide is a stable species, while copper(II) iodide does not exist.

For the complex reaction

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the log B(Beta) value is 1·88. Explain the value, giving the structure of A. [tren N(CH2CH2NH2)3] 10

What property/properties of lanthanide B-diketone complexes make(s) them useful as shift reagents in NMR spectroscopy?
What change in the position of iron in haemoglobin occurs in binding to oxygen and why? 5+5


Silicates produce a large number of silicate frameworks like
Al2(OH)4 Si205
Al2(OH)2 Si401O
Mg3(OH)2 Si4O10
KAl2(OH)2 Si3AlOIO
Na12 [(Al02)12(Si02)12]'xH20
Name the compounds D and E.

State whether the following statements are true or false, and if false, correct them: 10

It is possible to change the rate constant for a reaction by changing the temperature.
The reaction rate remains constant as a first-order reaction proceeds at a constant temperature.

Useful Constants and Integrals
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