Kerala PSC Range Forest Officer – Forest and Wildlife – (Chemistry) Previous Question Paper – 047/2025

The Commission publishes this paper without an answer key, so no answers are shown.

1. Calculate the wavelength of the spectral line with the highest energy in the Lyman series of the hydrogen spectrum. (R ≈ 1 × 10⁷ m⁻¹) (5)

2. Describe the quantum numbers of electron in the lowest energy orbital of the N-shell of an atom. (5)

3. 8.4 g of nitrogen and 2 g of hydrogen are mixed together to form ammonia. Calculate the number of moles of excess reactant.
+ (5)

4. “He2 molecule does not exist but He2 ion exist predominantly”. Justify using molecular orbital theory. (5)

5. Calculate the enthalpy of formation of benzene from the following thermochemical equations
(a) C 6 H 6( ) + 15O 2( ) → 6CO2 (g ) + 3H 2 O(l ) ΔH = −3200 kJ
l g
(b) C (s ) + O2( ) → CO2( ) ΔH = −390 kJ
g g
(c) H 2( ) + O2 → H2O(l ) ΔH = −280 kJ
g 2 () g (5)

6. For 2H₂O(g) + 2Cl₂(g) ⇌ 4HCl(g) + O₂(g), Kp = 30 atm at 27°C. Calculate Kc. Kp and Kc are the equilibrium constants in partial pressure and concentration; R = 0.0820 dm³ atm K⁻¹ mol⁻¹. (5)

7. Haber process is used to produce ammonia from nitrogen and hydrogen.
N 2( ) + 3H 2 (g ) g 2NH 3( ) ΔH = −92.4 kJ/Mol g
What will be the effect of
(a) Increase in pressure at constant temperature
(b) Increase in temperature at constant pressure
(c) Increase in concentration of nitrogen (5)

8. For the redox reaction
Zn (s ) + Cu2 + (0.1 M ) → Zn 2 + (1M ) + Cu (s )
E0 is 1.10 V cell
(a) Calculate Ecell of the reaction
(b) Write the half cell reactions (5)

9. Express Langmuir adsorption isotherm mathematically and graphically. What will happen this isotherm at very low pressure and very high pressure? (5)

10. Consider the reaction 2A + 2B → C + D. Experimental data: (i) [A] = 0.006, [B] = 0.001, rate = 0.012; (ii) [A] = 0.006, [B] = 0.002, rate = 0.024; (iii) [A] = 0.002, [B] = 0.0015, rate = 0.002; (iv) [A] = 0.004, [B] = 0.0015, rate = 0.008 (concentrations in mol dm⁻³ and rates in mol dm⁻³ s⁻¹). Given rate ∝ [A]ᵃ[B]ᵇ: (a) write the order with respect to A and B; (b) write the overall order; (c) calculate the rate constant. (5)

11. Calculate the mole fraction of water in a mixture containing 9 g water, 60 g acetic acid and 92 g ethanol. (Molecular mass of water = 18, acetic acid = 60 and ethanol = 46) (5)

12. Write any five differences between physisorption and chemisorption. (5)

13. Among the two octahedral complexes of Cobalt (III), the one with NH3 ligand is diamagnetic, while the one with fluoride ligand is paramagnetic. Justify this observation using Valence Bond Theory (VBT)
Using Crystal Field Theory (CFT), explain why [Fe (CN )6 ] 4− (5)

14. is a low-spin and diamagnetic complex, whereas [Fe (H O) ] is a high-spin and 2 6 2+
paramagnetic complex. (5)

15. Compare the packing efficiency of Face-Centered Cubic (FCC) and Body- Centered Cubic (BCC) unit cells and explain why FCC structures are more densely packed. (5)

16. An element X crystallizes in a face-centered cubic (FCC) structure. The atomic radius of X is 141.4 pm. The mass of 1020 atoms of X is given as 0.01 g. Calculate the density of X. (Avogadro’s number, NA = 6 × 1023) (5)

17. Uranium-235 undergoes nuclear fission to produce krypton-92, Barium-141 and three neutrons.
(a) Write the balanced nuclear reaction. (1)
(b) Calculate the total energy released if the energy per fission reaction is
200 MeV and 2 grams of 92 U undergo complete fission. (2)
(c) The mass of Uranium-235 nucleus is 235.04 u and the sum of the
masses of the fission products and neutrons is 234.92 u. Calculate the packing fraction of Uranium-235. (2) (5)

18. Radioisotopes have significant applications in medicine, industry and archaeology.
(a) How is Technetium-99m used in medical imaging? Why is it preferred
over other radioisotopes? (2)
(b) Explain how Carbon-14 dating helps in determining the age of
ancient fossils. What is the limitation of this method? (2)
(c) In industrial applications, how is Cobalt-60 used for material testing?
Explain the principle behind its working. (1) (5)

19. Qualitative analysis of cations and anions is based on principles like solubility product and the common ion effect.
(a) Explain how the common ion effect influences the precipitation of a
sparingly soluble salt. (2)
(b) In the qualitative analysis of cations, Group II cations (Pb2+, Hg2+,
Cu2+, etc.) are precipitated as sulfides. How does the solubility product (Ksp) principle help in their selecting precipitation? (2)
(c) A solution contains Ni2+ and Pb2+ ions. How can you distinguish
between them using a spot test with dimethylglyoxime and sodium rhodizonate? (1) (5)

20. Understanding molecular bonding and shape is essential for predicting chemical properties and reactivity.
(a) The bonding in ionic compounds is not 100% ionic and bonding in
covalent compounds is not 100% covalent. Explain this statement using Fajan’s rule and provide examples where covalent character is observed in ionic compounds. (2)
(b) Using VSEPR theory, predict and explain the shape of SF4 and ClF3.
(2)
(c) Both BF3 and NH3 and AX3-type molecules. However, their
geometries are different. Explain the reason. (1) (5)

21. How will you prepare mesityloxide from acetone? Write the mechanism for the reaction. (5)

22. Write the IUPAC name of the following compounds.
(a) (b)
(c) (d)
(e) (5)

23. Write the reaction and mechanism for the preparation of benzoic acid from benzene. (5)

24. Suggest a method for the conversion of phthalimide for ethylamine. Write the steps involved in the reaction. (5)

25. Which of the following compounds are chiral? Justify your answer.
(a) 2-chloropentane
(b) 3-methyl-1-Hexane
(c) 3-methyl hexane
(d) 5-ethyl 3,3-dimethylpentane
(e) 3-methylpentane (5)

26. Compound (A) C6H7N, on diazotisation yield (B) which then reaction with cuprous chloride to form (C). Identify A, B and C and show the reactions involved. (5)

27. (a) Assign E/Z notation applicable to the following systems with proper
explanation.
(I) (II)
(b) Assign R or S configuration to each of the following compounds.
(i)
(ii) (5)

28. Arrange the following compounds in the increasing order of acidity and explain your answer.
Cl 3COOH , H3C COOH , ClCH2COOH , H COOH , Cl | CH3 − CH − COOH (5)

29. Identify A, B and C in the following reaction sequence and write the reaction mechanism. (5)

30. Write the structures from A to E in the following reaction sequence. (5)

31. Explain the phenomena of muterotation exhibited by glucose with the help of its open chain and cyclic structures? Does fructose and glucose form the same osazone? Justify your answer with relevant equation. (5)

32. Explain and comment on the significance of each structure of protein? Also briefly outline the mechanism of enzyme catalysis proposed by Michaelis and Menten. (5)

33. Explain the relevance of the following terms with respect to DNA and RNA: Replication, Transcription, Translation, Genetic code and Mutation. (5)

34. Discuss the principle, applications and advantages of thin layer chromatography. (5)

35. What is the difference between fluorescence and phosphorescence in terms of persistence of light emission? Account for the difference. (5)

36. Compare the Grotthus-Draper Law and the Stark-Einstein Law taking photosynthesis as an example. (5)

37. Briefly describe the role of catalyst in Contact Process. Explain any three characteristics of a catalyst taking Contact Process as an example. (5)

38. Write the Van der Waals equation for one mole of a real gas and explain the significance of the constants ‘a’ and ‘b’. How does the Van der Waals equation provide a better description of real gases compared to the ideal gas law? (5)

39. What are properties of nanomaterials and how are they synthesized? (5)

40. Discuss the causes and effects of Greenhouse effect. (5)