CSS Chemistry Past Paper 2023

Instructions specific to this paper

• Attempt ONLY FOUR questions from PART-II. ALL questions carry EQUAL marks.
• Use of calculator is allowed.
• Attempt ONLY FOUR questions from PART-II. ALL questions carry EQUAL marks.

Questions

1. Q. 220 marks

   (a) The following reaction occurs via two steps, where the first step is rate- (12) determining step. Step I NO 2 (g) + NO 2 (g) → NO(g) + NO 3 (g) Step II NO 3 (g) + CO(g) → NO 2 (g) + CO 2 (g) i. Write down the rate equation for the above reaction. ii. Which molecule acts as a catalyst in this reaction? Give a reason. iii. Which molecule is an intermediate in this reaction and justify it. (b) Describe Arrhenius’s equation. (8)

2. Q. 310 marks

   (a) An explosion is usually considered adiabatic, indicating negligible heat transfer, even though it’s rapidly expanding gaseous products are not at the same temperature as the surroundings, and the boundary permits heat transfer. Explain the phenomenon. (b) Draw a working diagram for a reversible heat engine that operates with two (10) (20) isothermal steps and two constant-pressure steps. How many heat reservoirs are needed to operate this engine?

3. Q. 420 marks

   (a) Describe Schrodinger Wave Equation for a particle in a three-dimensional box. (10) (b) Explain photoelectric effect. (8) (c) What is a wave function? Give Born’s interpretation of wave function. (2)

4. Q. 520 marks

   (b) Describe Nernst’s equation. (10) (b) Describe the significance of pH, pK a , and pK b . (6) (c) What is the relationship between conductance and Kohlrausch’s law? (4)

5. Q. 620 marks

   (a) Describe three methods of mechanical phase separation. (10) (b) Briefly discuss “The Hard-Soft Acid-Base Principle.” (10)

6. Q. 710 marks

   (a) Compare Valence Bond Theory with Molecular Orbital Theory. (b) What is the oxidation state? Differentiate between the oxidation state and valency (6) /covalency of an element with suitable examples. (c) Write the molecular orbital configuration of the followings: (4) (20) + − −2 O 2 , O 2 , O 2 and O 2

7. Q. 820 marks

   Discuss the following in detail. (5 each) i. Crystal Field Theory ii. Hess’s Law iii. Electrophoresis Technique iv. Freundlich Adsorption Isotherm

Standard FPSC instructions

Printed on this and every CSS paper.

• Part-II is to be attempted on the separate Answer Book.
• All the parts (if any) of each question must be attempted at one place instead of at different places.
• Write Q. No. in the Answer Book in accordance with Q. No. in the question paper.
• No page/space be left blank between the answers. All the blank pages of the Answer Book must be crossed.
• Extra attempt of any question or any part of the attempted question will not be considered.