Class 12 Chemistry Complete Notes — Solid State to Biomolecules

Unit 1: Solid State

Types of Solids: | Type | Particles | Forces | Properties | Examples | |---|---|---|---|---| | Ionic | Ions | Electrostatic | Hard, high mp, conducts when molten | NaCl, MgO | | Covalent | Atoms | Covalent | Very hard, very high mp | Diamond, Quartz | | Metallic | Metal ions+electrons | Metallic | Lustrous, malleable, conducts | Fe, Cu | | Molecular | Molecules | vdW/H-bonds | Soft, low mp | Ice, glucose |

Crystal Systems: 7 types — Cubic, Tetragonal, Orthorhombic, Hexagonal, Trigonal, Monoclinic, Triclinic

Unit Cell Types (Cubic):

• Simple Cubic (SC): 1 atom/cell; packing efficiency 52%
• Body-Centered Cubic (BCC): 2 atoms/cell; PE 68%
• Face-Centered Cubic (FCC): 4 atoms/cell; PE 74% (most efficient)

Defects:

• Schottky: cation + anion both missing → decreases density
• Frenkel: cation displaced to interstitial site → density unchanged
• F-centres: electrons trapped at anion vacancies → colour

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Unit 2: Solutions

Concentration Terms:

• Molarity (M) = moles of solute/volume of solution in litres
• Molality (m) = moles of solute/kg of solvent
• Mole fraction (x) = moles of component/total moles
• ppm = mass of solute × 10⁶ / mass of solution

Raoult's Law: p_A = p°_A × x_A (partial pressure of A)

Colligative Properties (depend on number of solute particles, not identity):

1. Relative vapour pressure lowering: Δp/p° = x_solute
2. Boiling point elevation: ΔT_b = K_b × m
3. Freezing point depression: ΔT_f = K_f × m
4. Osmotic pressure: π = MRT (M=molarity, R=gas const, T=temperature in K)

Van't Hoff factor (i): Ratio of observed colligative effect to calculated

• i > 1: dissociation (NaCl → Na⁺ + Cl⁻, i=2)
• i < 1: association (acetic acid dimerization)

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Unit 3: Electrochemistry

Galvanic Cell (Voltaic Cell): Converts chemical energy to electrical energy

• Anode: Oxidation (negative electrode)
• Cathode: Reduction (positive electrode)
• Standard cell potential: E°cell = E°cathode - E°anode

Nernst Equation: E = E° - (RT/nF)ln Q = E° - (0.0592/n)log Q at 25°C

Electrolytic Cell: Electrical energy converts to chemical energy (electrolysis)

• Cathode: Reduction (gains electrons from power supply)
• Anode: Oxidation (loses electrons to power supply)

Faraday's Laws:

1. Mass deposited ∝ charge passed
2. Same charge deposits different masses for different elements → proportional to equivalent mass

Conductance:

• Conductance G = 1/R (Siemens, S)
• Molar conductance Λ_m = κ × 1000/M
• For strong electrolytes: Λ_m = Λ°_m - K√C (Debye-Hückel-Onsager)
• For weak electrolytes: α = Λ_m/Λ°_m (degree of dissociation)

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Unit 4: Chemical Kinetics

Rate of Reaction: Δ[product]/Δt = -Δ[reactant]/Δt

Rate Law: r = k[A]^m [B]^n

• k = rate constant; m,n = orders; m+n = overall order

Integrated Rate Laws:

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

Activation Energy (Arrhenius Equation): k = Ae^(-Ea/RT) ln(k₂/k₁) = (Ea/R)(1/T₁ - 1/T₂)

Catalyst: Lowers activation energy → increases rate. Not consumed in reaction.

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Unit 5: Coordination Chemistry

Werner's Theory:

• Primary valence = oxidation state (ionizable)
• Secondary valence = coordination number (non-ionizable)

Nomenclature Rules:

• Ligands named first, then metal
• Anionic ligands: -o suffix (chloro, cyano, nitro)
• Neutral ligands: aqua, ammine, carbonyl

Example: [Co(NH₃)₆]³⁺ = Hexaamminecobalt(III) ion

Valence Bond Theory (VBT):

• Inner orbital complex: uses (n-1)d orbitals → low spin, diamagnetic
• Outer orbital complex: uses nd orbitals → high spin, paramagnetic

Crystal Field Theory:

• d-orbitals split in presence of ligands
• d_x²-y², d_z² (e_g) → higher energy
• d_xy, d_xz, d_yz (t_2g) → lower energy
• Δ (splitting energy) depends on ligand strength

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Unit 6: Organic Chemistry

Haloalkanes and Haloarenes

Nucleophilic Substitution:

• SN₁: Two steps; carbocation intermediate; stereochemistry — racemization
• SN₂: One step; backside attack; complete inversion (Walden inversion)

Elimination vs Substitution:

• Strong bulky base → elimination
• Strong nucleophile → substitution
• Tertiary alkyl halides → prefer SN₁ and E1

Alcohols, Phenols, Ethers

• Primary alcohol → Aldehyde → Carboxylic acid (oxidation)
• Secondary alcohol → Ketone (oxidation)
• Tertiary alcohol → Cannot be oxidized easily

Lucas Test: Distinguish primary/secondary/tertiary alcohols

• Tertiary: immediate cloudiness (most reactive)
• Secondary: cloudiness after 5 min
• Primary: no reaction at room temperature

Aldehydes and Ketones

Nucleophilic Addition (characteristic of carbonyl compounds)

• Aldehyde more reactive than ketone (steric + electronic)
• Tollens' test (silver mirror) — only aldehydes
• Fehling's test (brick red ppt) — only aldehydes
• Iodoform test — methyl ketones and acetaldehyde

Carboxylic Acids

Acidity order: Electron-withdrawing groups increase acidity

• Chloroacetic > Acetic > Benzoic acid (pKa comparison)

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Biomolecules

Carbohydrates:

• Monosaccharides: glucose, fructose (C₆H₁₂O₆)
• Disaccharides: sucrose (glucose+fructose), maltose, lactose
• Polysaccharides: starch (energy storage), cellulose (structural in plants), glycogen (energy in animals)

Proteins:

• Built from amino acids linked by peptide bonds
• Primary structure: sequence of amino acids
• Secondary: α-helix or β-pleated sheet (H-bonds)
• Tertiary: 3D folded structure (overall shape)
• Quaternary: multiple polypeptide chains

Nucleic Acids:

• DNA: double helix; deoxyribose; bases ATGC; A pairs with T (2 H-bonds), G pairs with C (3 H-bonds)
• RNA: single strand; ribose; bases AUGC; carries genetic info from DNA to ribosomes

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Solved PYQs

Q1 (2023): The conductivity of 0.01 M acetic acid is 1.65×10⁻⁴ S/cm. Find molar conductance. Λ_m = κ × 1000/M = 1.65×10⁻⁴ × 1000/0.01 = 16.5 S·cm²/mol

Q2 (2023): Rate constant of first-order reaction is 0.0693 min⁻¹. Find half-life. t₁/₂ = 0.693/k = 0.693/0.0693 = 10 minutes

Q3 (2022): Write IUPAC name of [Pt(NH₃)₂Cl₂] Diamminedichloridoplatinum(II) (Two ammine ligands, two chlorido ligands, Pt in +2 state)

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Quick Revision Checklist

• FCC packing efficiency 74%; BCC 68%; SC 52%
• Raoult's Law and 4 colligative properties
• Nernst equation: E = E° - 0.0592/n × log Q
• First-order half-life: t₁/₂ = 0.693/k
• Arrhenius: k increases with temperature
• SN1 (two steps, carbocation) vs SN2 (one step, inversion)
• Tollens' test: only aldehydes; Iodoform: methyl ketones
• DNA bases: A-T (2 H-bonds), G-C (3 H-bonds)