Class 12 Chemistry — Complete Notes and CBSE PYQs

Chapter 3: Electrochemistry

Electrolytic Cells vs Electrochemical Cells

| Feature | Electrochemical Cell | Electrolytic Cell | |---|---|---| | Energy | Chemical → Electrical | Electrical → Chemical | | Reaction | Spontaneous | Non-spontaneous | | Anode | Negative terminal | Positive terminal | | Cathode | Positive terminal | Negative terminal | | Examples | Battery, fuel cell | Electroplating, electrolysis |

Cell EMF and Thermodynamics

Nernst Equation: E = E° - (RT/nF) ln Q = E° - (0.0591/n) log Q (at 25°C)

Relationship:

• ΔG° = -nFE° (n = moles of electrons, F = 96500 C/mol)
• ΔG° = -RT ln K
• Therefore: log K = nE°/0.0591

Standard Electrode Potentials (E°):

• More positive E° → stronger oxidizing agent → cathode in cell
• More negative E° → stronger reducing agent → anode in cell
• Cell EMF = E°cathode - E°anode

Faraday's Laws of Electrolysis:

1. Mass deposited ∝ quantity of electricity (Q = It)
2. Mass deposited ∝ equivalent weight for same Q

Mass deposited: m = (M × I × t) / (n × F)

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Chapter 4: Chemical Kinetics

Rate of Reaction: Change in concentration per unit time. Rate = -d[R]/dt = d[P]/dt

Rate Law: Rate = k[A]^x [B]^y (x,y = order from experiment, not stoichiometry!)

Integrated Rate Laws:

| Order | Rate Law | Integrated Form | Half-life t₁/₂ | |---|---|---|---| | Zero | Rate = k | [A] = [A]₀ - kt | [A]₀/2k | | First | Rate = k[A] | ln[A] = ln[A]₀ - kt | 0.693/k | | Second | Rate = k[A]² | 1/[A] = 1/[A]₀ + kt | 1/(k[A]₀) |

Arrhenius Equation: k = A·e^(-Ea/RT) ln(k₂/k₁) = (Ea/R)(1/T₁ - 1/T₂)

• Ea = activation energy; higher Ea → more temperature sensitive

Activation energy: Minimum energy needed for reaction to occur. Catalyst: Provides alternative pathway with lower Ea.

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Chapter 5: Surface Chemistry

Adsorption: Accumulation of substance on surface.

• Physisorption: Weak van der Waals forces, reversible, low temperature
• Chemisorption: Chemical bond formed, irreversible, high temperature, specific

Colloids:

• Particle size: 1–1000 nm (between solution and suspension)
• Sol: Solid in liquid (gold sol)
• Emulsion: Liquid in liquid (milk)
• Gel: Liquid in solid (butter, cheese)
• Aerosol: Solid/liquid in gas (fog, smoke)

Tyndall Effect: Scattering of light by colloidal particles (beam visible in colloid but not in true solution).

Coagulation: Aggregation of colloidal particles; caused by electrolytes. Hardy-Schulze Rule: Higher valence ion more effective at coagulation.

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Chapter 8: d and f Block Elements

d-Block (Transition Metals): Groups 3-12, filling of 3d/4d/5d orbitals.

Properties of Transition Metals:

• Variable oxidation states (due to close energy of ns and (n-1)d orbitals)
• Colored ions (d-d transitions in visible light)
• Paramagnetic (unpaired d electrons)
• Catalytic activity
• Tendency to form complexes

Mn oxidation states: +2, +3, +4, +6, +7 (widest range) Fe: +2 (Fe²⁺, pale green), +3 (Fe³⁺, yellow-brown) Cu: +1 (Cu⁺, colorless), +2 (Cu²⁺, blue)

KMnO₄ (Potassium Permanganate):

• In acidic medium: MnO₄⁻ → Mn²⁺ (5 electrons; purple to colorless)
• In neutral/alkaline medium: MnO₄⁻ → MnO₂ (3 electrons; brown ppt)

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Chapter 9: Coordination Compounds

Complex/Coordination Compound: Central metal ion bonded to ligands (Lewis bases).

Werner's Theory:

• Primary valence: oxidation state (ionizes)
• Secondary valence: coordination number (doesn't ionize)

IUPAC Nomenclature: Format: [ligands alphabetically + metal name (oxidation state)]

• Anionic ligands: add -o (Cl⁻ = chloro, CN⁻ = cyano, OH⁻ = hydroxo, NO₂⁻ = nitrito)
• Neutral ligands: name as is (H₂O = aqua, NH₃ = ammine, CO = carbonyl)
• Multiple ligands: di, tri, tetra; or bis, tris, tetrakis for complex names

Example: [Co(NH₃)₄Cl₂]⁺ = Tetraamminedichloridocobalt(III) ion

Common Geometries:

• CN 2: Linear
• CN 4: Square planar (d⁸: Pt²⁺, Pd²⁺, Ni²⁺, Au³⁺) or Tetrahedral
• CN 6: Octahedral (most common for 3d transition metals)

Isomerism in Coordination Compounds:

• Structural: ionization, hydrate, linkage, coordination
• Stereoisomerism: geometric (cis-trans), optical (non-superimposable mirror images)

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Organic Chemistry

Chapter 10: Haloalkanes and Haloarenes

Nucleophilic Substitution Reactions:

SN2 Reaction (Bimolecular):

• One step, backside attack by nucleophile
• Rate = k[substrate][nucleophile]
• Inversion of configuration (Walden inversion)
• Order: Methyl > Primary > Secondary (Tertiary doesn't react)

SN1 Reaction (Unimolecular):

• Two steps: carbocation intermediate formed
• Rate = k[substrate] (first order)
• Racemization (50:50 mixture of configurations)
• Order: Tertiary > Secondary > Primary (Methyl doesn't react)

Chapter 13: Amines

Classification: Primary (RNH₂), Secondary (R₂NH), Tertiary (R₃N)

Basicity order: 2° > 1° > 3° > NH₃ (in aqueous solution due to solvation) Gas phase: 3° > 2° > 1° > NH₃

Distinguishing tests:

• Hinsberg's test: Reacts with benzenesulfonyl chloride; 1° → soluble ppt, 2° → insoluble ppt, 3° → no reaction
• Carbylamine reaction: 1° amines + CHCl₃ + KOH → isocyanide (foul smell) — specific to 1° amines

Chapter 15: Polymers

Types by structure:

• Addition polymers: Monomer with double bond (no byproduct): polyethylene, PVC
• Condensation polymers: Two different monomers, small molecule released: nylon, polyester, bakelite

Types by behavior:

• Thermoplastics: Soften on heating, reshape (HDPE, PVC, nylon)
• Thermosetting: Permanently hard after forming (bakelite, melamine, epoxy)

| Polymer | Monomer(s) | Type | Use | |---|---|---|---| | Polyethylene | CH₂=CH₂ | Addition | Bags, bottles | | PVC | CH₂=CHCl | Addition | Pipes, cables | | Nylon-6,6 | Adipic acid + Hexamethylenediamine | Condensation | Fibers, ropes | | Bakelite | Phenol + Formaldehyde | Condensation | Electrical switches | | Natural rubber | Isoprene | Addition | Tyres |

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Solved CBSE PYQs

Q1 (2023): Calculate the EMF of cell: Zn|Zn²⁺(0.1M)||Cu²⁺(1M)|Cu. E°cell = 1.10V E = E° - (0.0591/2) log([Zn²⁺]/[Cu²⁺]) E = 1.10 - (0.0591/2) log(0.1/1) = 1.10 - 0.02955 × (-1) = 1.13V

Q2 (2022): Rate constant of first order reaction is 2×10⁻³ min⁻¹. Find half-life. t₁/₂ = 0.693/k = 0.693/(2×10⁻³) = 346.5 minutes

Q3 (2024): Give IUPAC name: [Pt(NH₃)₂Cl₂] Ligands: 2 ammine (a), 2 chlorido (c) — alphabetical: ammine before chlorido Metal: platinum, charge: 0 = Pt²⁺ if 2 NH₃(0) + 2 Cl⁻(-2) = neutral complex Name: Diamminedichloridoplatinum(II)

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Quick Revision Checklist

• Electrochemical cell: cathode positive (reduction), anode negative (oxidation)
• Nernst equation: E = E° - 0.0591/n × log Q
• ΔG° = -nFE°
• First order t₁/₂ = 0.693/k (independent of concentration)
• Physisorption vs chemisorption
• Tyndall effect: light scattering in colloids
• Transition metals: variable OS, colored, paramagnetic
• IUPAC naming: ligands alphabetically + metal(OS)
• SN1 vs SN2: mechanism, order, configuration change
• Polymer types: addition vs condensation, thermoplastic vs thermosetting