Sample Paper | ISC Chemistry | Physical Chemistry | 2021 exam

Important Questions based on Scope of Syllabus for
 2021 ISC chemistry examination and latest trends in ISC question papers.

PHYSICAL CHEMISTRY (THEORY) (50 min.)

(Candidates are allowed additional 10 minutes for only reading the paper

They must NOT start writing during this time)

All questions are compulsory Question 1 is of 10 marks having three sub parts all of which are compulsory. Question numbers 2 - 4 carry 2 marks, Question numbers 5 -7 carry 3 marks, Question numbers 8 carry 5 marks. The intended marks for questions or part of questions are given in brackets [ ]. Balanced equations must be given wherever possible and diagrams where they are helpful. When solving numerical problems, all essential working must be shown. In working out problems, use the following data: Gas constant R = 1.987 cal deg -1mol -1 = 8.314 JK -1 mol-1 = 0.0821 dm 3 atm K -1 mol -1 , 1 l atm = 1 dm 3 atm = 101.3 J 1 Faraday = 96540 coulombs

Question 1:

[A] Choose the most appropriate word to complete the following statement.                                             [3]

[doubles, four, zero, second, chemical, electrical, more, less]

(a)     When the concentration of a reactant of first order reaction is doubled, the rate of reaction becomes……………. times, but for a ……………. order reaction, the rate of reaction remains the same.

(b)    A Galvanic cell converts …………… energy into…………. energy.

(c)     The elevation of boiling point of 1 M K₂SO₄ solution is …………...that of 1 M urea solution. The elevation of boiling point of 1 M KCl solution is …………… that of 1 M K₂SO₄ solution.

[B] Choose the correct alternative.                                                                                                                 [3]

(a)     If the concentration of one of the reactants in a chemical reaction is increases, the rate of the reaction usually

      (i) decreases                                 (ii) increases                                      (iii) remains the same

(b)    An increase in temperature increases the rate of a chemical reaction because the

     (i) Activation energy increases                          (ii) activation energy decreases

    (iii) Number of molecular collisions increases     (iv) number of molecular collisions decreases

(c)     A reaction was found to be second order with respect to the concentration of carbon monoxide. If the concentration of carbon monoxide is doubled, with everything else kept the same, the rate of reaction will

   (i) Double           (ii) remain unchanged               (iii) triple              (iv) increase by a factor of 4

[C] Answer the following.                                                                                                                             [4]

(a)     What is the effect of frenkel defect on the density of solids?

(b)    Define piezoelectricity and give one use of piezoelectric crystals.

(c)     Why is MgSO₄ more effective than NaCl in coagulating a Fe(OH) ₃ dispersion in water?

(d)    What is peptization.

 Question 2: What is electrophoresis? In what respects do is differing from electrolysis?                            [2]

Question 3: A first order reaction taken 80 minutes for the completion of 50 percent of reaction. Find the time when 75 percent of the reaction will be completed.                                                                                                      [2]

Question 4: The slope of the line in the graph of log k versus 1/T for a reaction is -5841 K. Calculate the energy of activation for this reaction.                                                                                                                              [2]

Question 5: Silver crystallizes with face-centered cubic unit cells. Each side of the unit cell has a length of 409pm. What is the radius of an atom of silver? (Assume that each face atom is touching the four corner atoms.)             [3]

Question 6:  A solution of a non-volatile solute in water freezes at -0.30ºC, the vapour-pressure of pure water at 298 k is 23.51 mm Hg and k_f for water is 1.86 K kg mol^-1. Calculate the vapour-pressure of this solution 298 K.     [3]

Question 7: When 0·4g of oxalic acetic acid is dissolved in 40g of benzene, the freezing point of the solution is lowered by 0·45K. Calculate the degree of association of acetic acid. Acetic acid forms dimer when dissolved in benzene.  

   (K_f for benzene = 5·12 K kg mol^-1, at. wt. C = 12, H = 1, O = 16)                                                               [3]

Question 8:

(a)     If E° of copper electrode is +0.34 V, how will you calculate its EMF value when the solution in contact with it is 0.1 M in copper ions? How does EMF for copper electrode change when concentration of Cu²⁺ ions in the solution is decreased?                                                                                                                                      [3]

(b)    Define the following terms:                                                                                                                        [2]

(i)    Molar conductivity

(ii)   Kohlrausch’s Law

or

(c)     Calculate emf of the following cell at 298 K and maximum possible work done by the Cell.                [3]

Mg(s) | Mg²⁺ (0·1 M) || Cu²⁺(0·01M) | Cu(s)

[Given E^o cell = +2·71 V, 1 Faraday = 96500 C mol^-1]

(d)    State Faraday’s first law of electrolysis. Calculate the charge required in terms of Faraday for the reduction of 2 mole of Zn²⁺ to Zn.                                                                                                                                             [2]