NSEC cheat sheet

Chemistry (CBSE Class 12 and below)

• Mole concept: n = m/M = N/N_A = V/22.4 L at STP (273.15 K, 1 bar); molarity M = moles solute / litres solution, molality m = moles solute / kg solvent; dilution obeys M1V1 = M2V2.

• Colligative properties: ΔTb = i·Kb·m, ΔTf = i·Kf·m, π = iCRT; van't Hoff factor i = observed/normal value; for water Kf = 1.86 K·kg·mol⁻¹ and Kb = 0.52 K·kg·mol⁻¹.

• Electrochemistry: Nernst equation E = E° − (0.0591/n)·log Q at 298 K; ΔG° = −nFE° = −2.303RT log K; 1 F = 96500 C·mol⁻¹; molar conductivity Λm = κ/c (κ in S·cm⁻¹, c in mol·cm⁻³).

• Chemical kinetics: first-order k = (2.303/t)·log(a/(a−x)); t½ = 0.693/k for first order, t½ = a/(2k) for zero order; Arrhenius k = A·e^(−Ea/RT), so log(k2/k1) = (Ea/2.303R)(1/T1 − 1/T2).

• Equilibrium and pH: Kw = [H⁺][OH⁻] = 1×10⁻¹⁴ at 298 K; pH = −log[H⁺]; for a weak acid pH = ½(pKa − log c); Henderson–Hasselbalch pH = pKa + log([salt]/[acid]); Kp = Kc(RT)^Δn.

• Periodic trends: across a period, atomic radius and metallic character decrease while ionisation enthalpy, electron gain enthalpy (more negative) and electronegativity increase; down a group the reverse holds; noble-gas radii are van der Waals, not covalent, radii.

• Organic reaction rules: Markovnikov addition to alkenes (H to carbon with more H), anti-Markovnikov with HBr/peroxide (free-radical), SN1 favoured by 3° halides/polar protic solvents, SN2 by 1° halides/polar aprotic solvents; Saytzeff alkene is the more substituted one.

• Named reactions and tests: Cannizzaro (aldehyde without α-H disproportionates), Aldol (α-H aldehyde/ketone), Reimer–Tiemann, Kolbe, Friedel–Crafts acylation/alkylation; Tollens and Fehling test aldehydes, iodoform test CH3CO–/CH3CH(OH)– groups.

• Coordination and bonding: VSEPR AXmEn gives linear, trigonal planar, tetrahedral, trigonal bipyramidal and octahedral shapes; crystal field splitting gives high-spin/low-spin d-configurations; hybridisation from steric number (2 = sp, 3 = sp², 4 = sp³).