Chemistry: Physical, Organic, and Inorganic
Chemistry on SITEEE covers physical, organic, and inorganic chemistry from the Class 11–12 syllabus: mole concept, equilibrium, thermodynamics, electrochemistry, bonding, hydrocarbons, functional groups, coordination compounds, and biomolecules. Questions often ask you to link a calculation to a structural idea.
Core rules and concepts
- Mole relation: n = m/M; molarity = moles of solute / litres of solution. At STP, an ideal gas occupies about 22.4 L per mole.
- Equilibrium: Le Chatelier's principle predicts shifts; for a weak acid, Ka = [H+][A-]/[HA] and pH = -log[H+].
- Thermodynamics: ΔG = ΔH - TΔS; a reaction is spontaneous when ΔG < 0. Hess's law allows enthalpy cycles.
- Organic: identify the functional group and its priority; distinguish inductive, resonance, and steric effects; apply Markovnikov's rule and SN1/SN2 conditions.
- Inorganic: use periodic trends, VSEPR shapes, and oxidation state rules; in coordination compounds, separate oxidation state from coordination number.
Worked example
A 0.10 M solution of a weak monoprotic acid HA has pH 3.0. Find Ka. Since pH = 3.0, [H+] = 10^-3 M. For HA ⇌ H+ + A-, [A-] is also about 10^-3 M, and [HA] ≈ 0.10 - 10^-3 ≈ 0.10 M. Thus Ka = (10^-3)(10^-3)/0.10 = 1.0 × 10^-5. The approximation is valid because the ionized fraction is only about 1%.
Traps
Using pH instead of [H+] in Ka; forgetting to subtract ionized acid when the approximation fails; confusing molarity with molality; assigning the wrong priority to functional groups; mixing oxidation state with coordination number.