CSS 2026 Chemistry Paper I Past Paper

Paper details

Examination

CSS

Year

2026

Subject

Chemistry

Paper

Paper One

Subject type

Optional

Mode

Subjective

Questions recorded from this paper

These 6 question wordings are transcribed from CSS Vista’s structured Chemistry past-paper record for CSS 2026.

1. Q5 · photoelectric effect(a) Explain the photoelectric effect and how it supports the particle nature of light. Discuss the role of work function and threshold frequency. (b) Explain the common ion effect and its application in controlling the solubility of sparingly soluble salts. Use an example to illustrate. (c) Explain the mechanism of enzyme catalysis, highlighting the role of the active site and the factors that influence enzyme activity.
2. Q6 · Debye-Hückel theory and activity coefficient(a) Use VSEPR to predict the shape and bond angles of $SF_4$ and explain the concept of stereochemically active lone pairs. (b) Using the Van der Waals equation, explain qualitatively how critical constants (Tc, Pc, Vc) relate to a, b parameters. (c) Explain Debye-Hückel theory and derive the limiting law for the mean ionic activity coefficient. Describe its region of validity.
3. Q2 · physical adsorption and chemisorption(a) Explain the difference between physisorption and chemisorption in terms of energetics and kinetics. Provide typical experimental evidence to distinguish them. (b) Define and explain the concepts of internal energy (E) and enthalpy (H). Show the mathematical relationship between them. (c) Discuss the physical meaning of eigenfunctions and eigenvalues, and explain why operators must be Hermitian in quantum mechanics.
4. Q3 · Chromatography(a) Outline selection criteria for stationary and mobile phases in column chromatography for separating polar organic molecules. (b) Propose a corrosion prevention strategy for a steel water pipeline system exposed to chloride- rich environments. (c) Derive the integrated rate equation for a second-order reaction where two reactants of equal concentration react (2A \rightarrow Products).
5. Q4 · Jahn-Teller theorem(a) Given small sample data, compute 95% confidence interval for the mean and interpret the result. (b) Predict and justify which complex will undergo a stronger Jahn-Teller distortion: [Cu(H_2O)_6]^{2+}$ or $[Mn(H_2O)_6]^{3+}. Support your reasoning with electronic configurations and degeneracy arguments. (c) Explain how transport numbers are determined experimentally and derive their relationship with ionic mobilities.
6. Q7 · isomerism(a) Discuss isomerism in coordination complexes (geometric, optical, linkage) with three illustrative examples and draw structures. (b) A buffer is to be made at pH 5.00 using sodium phosphate salts. Which pair would you choose and how would you prepare it? Show calculations. (c) Explain valence bond theory and hybridization for methane (CH_4), and contrast it with an MO description of bonding in the same molecule.

Topic-wise Chemistry past-paper analysis.