GUJCET Chemistry: Physical, Inorganic and Organic in 40 MCQs
GUJCET Chemistry contributes 40 single-correct MCQs, 1 mark each with a 0.25 penalty for errors. It is common to PCM and PCB, and the GSEB Class 12 syllabus is split roughly evenly between physical, inorganic and organic chemistry. Physical questions are numerical; inorganic questions test trends, structures and qualitative tests; organic questions test reagents, mechanisms and isomer counting. Because options are often close, write the balanced equation or the mole ratio before selecting.
Core rules
- Stoichiometry: convert to moles first; identify the limiting reagent; use molar volume 22.4 L only at STP.
- Equilibrium: K_p = K_c(RT)^Δn; Le Chatelier shifts oppose a change but do not change K.
- Electrochemistry: E°cell = E°cathode − E°anode; ΔG° = −nFE°cell; dilution changes E via the Nernst term.
- Kinetics: first-order t½ = 0.693/k, independent of concentration; rate law is experimental, not read from the balanced equation.
- Organic: SN1 favours tertiary/carbocation-stabilised substrates; SN2 favours primary substrates and strong nucleophiles; Markovnikov addition gives the more stable carbocation.
- Coordination: count ligands and charge; [Ni(CN)₄]²⁻ is square planar dsp², while [NiCl₄]²⁻ is tetrahedral.
Worked example
Find the pH of 0.010 M acetic acid (K_a = 1.8×10⁻⁵). Let x = [H⁺]. K_a = x²/(0.010 − x) ≈ x²/0.010. Then x² = 1.8×10⁻⁷, x = 4.24×10⁻⁴ M. pH = −log(4.24×10⁻⁴) = 3.37. Check the approximation: x is 4.2% of 0.010 M, below the usual 5% cut-off, so the simplified quadratic is acceptable.
Traps that cost marks
- Reversing anode and cathode in the Nernst equation.
- Treating a strong acid as weak (or vice versa) and missing 100% dissociation.
- Forgetting that K_p uses partial pressures, not concentrations.
- Assigning R/S without ranking by atomic number at the first point of difference.
- In organic MCQs, ignoring stereochemistry or the possibility of rearrangement.
- Rounding intermediate logs too early.