Chemistry (PGT) — HTET Level 3 Study Notes

Overview

Chemistry at the PGT level for HTET covers the entire Class XI-XII NCERT syllabus across three major branches: Physical Chemistry, Organic Chemistry, and Inorganic Chemistry. This subject carries significant weightage in the Level 3 paper and tests both conceptual depth and application ability.

For HTET PGT Chemistry, expect questions that assess your command over fundamental principles, reaction mechanisms, periodic trends, and numerical problem-solving. The exam tests whether you can teach these concepts effectively to senior secondary students, so questions often focus on conceptual clarity rather than rote memorization.

Mastering this section requires balanced preparation across all three branches. Physical Chemistry demands numerical accuracy, Organic Chemistry requires understanding of mechanisms and named reactions, while Inorganic Chemistry needs systematic memorization of properties and exceptions.

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Key Concepts

**Physical Chemistry**

• **Atomic Structure**: Bohr model, quantum numbers, electronic configuration, Aufbau principle, Hund's rule, Pauli exclusion principle. Shapes of orbitals (s, p, d).
• **Chemical Thermodynamics**: First and second laws, enthalpy, entropy, Gibbs free energy. ΔG = ΔH − TΔS determines spontaneity.
• **Chemical Equilibrium**: Law of mass action, equilibrium constant (Kp, Kc), Le Chatelier's principle, ionic equilibrium, pH, buffer solutions.
• **Electrochemistry**: Nernst equation, electrochemical cells, EMF calculation, Faraday's laws, conductance and molar conductivity.
• **Chemical Kinetics**: Rate laws, order and molecularity, Arrhenius equation, activation energy, half-life calculations.

**Organic Chemistry**

• **IUPAC Nomenclature**: Naming of alkanes, alkenes, alkynes, alcohols, aldehydes, ketones, carboxylic acids and their derivatives.
• **Reaction Mechanisms**: SN1, SN2, E1, E2, electrophilic addition, electrophilic aromatic substitution, nucleophilic addition.
• **Named Reactions**: Wurtz, Cannizzaro, Aldol condensation, Friedel-Crafts, Sandmeyer, Kolbe, Hofmann bromamide.
• **Isomerism**: Structural isomerism (chain, position, functional), stereoisomerism (geometrical, optical), chirality and R/S configuration.
• **Biomolecules**: Carbohydrates, proteins, nucleic acids, vitamins — structures and functions.

**Inorganic Chemistry**

• **Periodic Properties**: Atomic radius, ionization energy, electron affinity, electronegativity — trends across periods and groups.
• **Chemical Bonding**: VSEPR theory, hybridization (sp, sp², sp³, sp³d, sp³d²), molecular orbital theory, hydrogen bonding.
• **Coordination Chemistry**: Werner's theory, IUPAC naming, isomerism, crystal field theory, colour and magnetic properties.
• **d-block and f-block Elements**: Properties of transition metals, lanthanide and actinide contraction, catalytic behaviour, alloy formation.
• **Metallurgy**: Extraction principles, reduction methods, refining techniques for important metals.

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Formulas / Key Facts

| Area | Formula/Fact | |------|-------------| | Ideal Gas | PV = nRT | | Kinetic Energy | KE = (3/2)RT per mole | | First Law | ΔU = q + w | | Gibbs Energy | ΔG = ΔH − TΔS; spontaneous if ΔG < 0 | | Equilibrium Constant | Kp = Kc(RT)^Δn | | pH | pH = −log[H⁺]; pOH = −log[OH⁻]; pH + pOH = 14 | | Nernst Equation | E = E° − (0.059/n) log Q at 25°C | | Arrhenius Equation | k = Ae^(−Ea/RT) | | Half-life (1st order) | t₁/₂ = 0.693/k | | Faraday's 1st Law | m = ZIt = (MIt)/(nF) | | Effective Atomic Number | EAN = Z − oxidation state + 2×(coordination number) |

**Must-Remember Facts:**

• Lanthanide contraction causes similar radii for Zr-Hf, Nb-Ta pairs
• SN2 proceeds with inversion (Walden inversion); SN1 gives racemization
• Markovnikov's rule: H adds to carbon with more H atoms in unsymmetrical addition
• CFSE is maximum for d³ and d⁸ configurations in octahedral field

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Worked Examples

**Example 1: Equilibrium Constant** *For the reaction N₂ + 3H₂ ⇌ 2NH₃, if Kc = 0.5 at 400 K, find Kp. (R = 0.082 L·atm/mol·K)*

**Solution:**

• Δn = moles of gaseous products − moles of gaseous reactants = 2 − (1+3) = −2
• Kp = Kc × (RT)^Δn
• Kp = 0.5 × (0.082 × 400)^(−2)
• Kp = 0.5 × (32.8)^(−2)
• Kp = 0.5 × (1/1075.84) = 4.65 × 10⁻⁴

**Example 2: Electrode Potential** *Calculate EMF of cell: Zn|Zn²⁺(0.01M)||Cu²⁺(0.1M)|Cu. Given E°(Zn²⁺/Zn) = −0.76V, E°(Cu²⁺/Cu) = +0.34V*

**Solution:**

• E°cell = E°cathode − E°anode = 0.34 − (−0.76) = 1.10 V
• Cell reaction: Zn + Cu²⁺ → Zn²⁺ + Cu; n = 2
• Q = [Zn²⁺]/[Cu²⁺] = 0.01/0.1 = 0.1
• E = E° − (0.059/2) × log(0.1)
• E = 1.10 − (0.0295) × (−1) = 1.10 + 0.0295 = **1.13 V**

**Example 3: Organic Reaction Mechanism** *Predict product: CH₃CH₂Br + NaOH (aqueous) → ?*

**Solution:**

• Primary alkyl halide with strong nucleophile favours SN2
• OH⁻ attacks carbon bearing Br from backside
• Product: CH₃CH₂OH (ethanol)
• Reaction proceeds with inversion at the carbon centre

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Common Mistakes

❌ **Confusing Kp and Kc units**: Kc is in concentration terms, Kp in pressure terms. Only equal when Δn = 0. ✅ **Correct approach**: Always calculate Δn first; use Kp = Kc(RT)^Δn.

❌ **Sign errors in electrode potential**: Subtracting potentials incorrectly when calculating cell EMF. ✅ **Correct approach**: E°cell = E°cathode − E°anode. The electrode with higher E° is cathode (reduction).

❌ **Mixing SN1 and SN2 conditions**: Assuming all substitutions follow one mechanism. ✅ **Correct approach**: SN2 needs strong nucleophile + primary/methyl substrate; SN1 needs weak nucleophile + tertiary substrate.

❌ **Forgetting exceptions in periodic trends**: Assuming all properties follow uniform trends. ✅ **Correct approach**: Remember exceptions — IE₁ of O < N (half-filled stability), EA of F < Cl (small size repulsion).

❌ **Wrong hybridization assignment**: Counting only bonds, ignoring lone pairs. ✅ **Correct approach**: Hybridization = (bond pairs + lone pairs) on central atom. H₂O: 2 bonds + 2 lone pairs = sp³.

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Quick Reference

• **Spontaneity**: ΔG < 0 (spontaneous), ΔG > 0 (non-spontaneous), ΔG = 0 (equilibrium)
• **Markovnikov**: In HX addition to alkene, H goes to C with more H; Anti-Markovnikov with peroxides for HBr only
• **Order of reactivity SN1**: 3° > 2° > 1° > CH₃ (carbocation stability)
• **CFSE order**: d⁶ low spin (Co³⁺) has maximum CFSE in octahedral field
• **Acidic strength of halogen acids**: HI > HBr > HCl > HF (bond strength decreases)
• **Buffer equation**: pH = pKa + log([salt]/[acid]) — Henderson-Hasselbalch equation