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Chemistry Kumaon University Solved 2006 Previous Year Paper

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Chemistry Kumaon University Solved Previous Year Paper
B.Sc. (Part –II) (T.D.S) Examination, 2006
CHEMISTRY – Paper – Third
Time; Three Hours]                          
 (Physical Chemistry)                                    
 [M.M.: 34

Section – A
1. Note – Attempt all question. All carries ½ marks.
        i.            If the series of changes in a cycle are conducted at constant temperature, the cycle is said to be a/an…………..
Answer. If the process is taking place at constant temperature then the cycle is known as isothermal cycle
Additional information:
*If the process is taking place reversibly then cycle is known as reversible cycle.
*The Carnot cycle is the best example of the cyclic process.
      ii.            The efficiency of a Carnot’s cycle should be………

q2 = qH Heat absorbed by colder reservoir from higher temperature body (T higher)
q1 = qL Heat evolved by hotter reservoir to lower temperature body (T lower)
W = Work.
    iii.            The work function (A) in thermodynamics is also known as………..
Answer. The Helmholtz energy
Additional information:
 *The Helmholtz energy, A = U − TS, where U is the internal energy, T is the thermodynamic (absolute) temperature, and S is the entropy of the system. At constant temperature, the change in work function is equal to the maximum work that can be done by a system (ΔA = wmax).
    iv.            What will be the effect of increase in pressure in the equilibrium?
22.4 Kcal.
Answer. An increase in pressure favors the forward reaction, and more ammonia is produced. (Because reaction proceeds by decrease in volume)
Additional information:
*Reaction is exothermic so less temperature is also required for the forward reaction.
*Catalyst = Fe, Promoter = Mo.
*High concentration of reactant is required.
      v.            Write the Gibb’s phase rule equation.
Answer. In heterogeneous system in equilibrium this rule can be defined mathematically as,
F = C – P +2
*Where, all three variables (Temperature, Pressure and Concentration) are considered.
Here, F = Degree of freedom, C = Component, P = phases,
    vi.            What will be the pH of a 0.05 N H2SO4 at 250C if it completely dissociated?
Here, Conversion of Normality into Molarity is a necessary step.

= 0.025 Mol/lit. For 1 H+

For complete Ionization of H2SO4

Molarity = [H+] = 2 X [H+]
= 2 X 0.025
=0.05 Mol/lit
  vii.            Define the critical solution temperature (C.S.T).
Answer. The temperature above (or below) which a pair of partially miscible liquids becomes miscible in all proportions, is called critical solution temperature or consolute temperature pair of partially miscible liquids.
viii.            Write the relation between the specific conductance and the equivalent conductance of an electrolytic solution.
    ix.            Calculate pKa of CH3COOH if Ka for CH3COOH is 1.8 X 10-5.

Answer. Relation between pKa and Ka is
pKa = - log Ka.
pKa = - log 1.8 X 10-5
= - [0.2553 + 5]
= 4.7447
      x.            What is the number of undissociated molecules of acetic acid in 6 g of acetic acid, if the dissociation of acetic acid is nil.
1 mol = 6.023 X 1023 molecules
6g = 0.1` mol = 6.023 X1022 CH3COOH undissociated molecules.
    xi.            Write the relation among Joule, Volt and Coulomb.
Answer. Volts to joules calculation formula:
The energy E in joules (J) is equal to the voltage V in volts (V), times the electrical charge Q in coulombs (C)
Joule = volt × coulomb
  xii.            Define standard electrode potential.
Answer. The tendency of an electrode to lose or gain electron, when it is in contact with its solution at standard condition viz., unit concentration, 1 atmospheric pressure and 250C temperature, is called Standard electrode potential or Normal electrode potential, represented by E0.
xiii.            Hydrolysis of salt of weak base and strong acid gives a/an ……..solution.
Answer. Acidic solution
Additional Information:
*Aqueous solution of
a)      Salts of weak acids and weak bases only. --------------- > Neutral
b)      Salts of weak acid and with strong bases.---------------- > Basic
c)      Salts of weak bases and strong acid. ---------------------- > Acidic
xiv.            What is ionic product of water at 250C?
Kw = [H+][OH-] = 1 X 10-14
at 250C.
Additional information:
*Product of two constant Kc and K gives another constant called dissociation of water or ionic product of water, Kw. i.e.
  xv.            , represents which law?
Kohlrausch’s Law; Where, the value  and are called ionic mobilities or ionic conductance, , equivalent conductivities of an electrolyte.
xvi.            Write Ostwald’s dilution law.
Answer. It is applicable for weak electrolyte. “It states that the degree of dissociation of weak electrolyte is directly proportional to the square root of dilution”.
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