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APEX CLASS ESTD 2018

IITJEE CHEMISTRY: Solid State & Surface Chemistry Visualizer

By

Ashish Kumar Bahekar

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APEX CLASS • IITJEE Physical Chemistry Lab

Solid State & Surface Chemistry Visualizer

Master Lattice Packing Efficiencies, Defects, Freundlich Isotherms, and Hardy-Schulze Coagulation!

🔬 Select a Unit Cell or Defect Concept:
Simple Cubic (SC) Z = 1 | a = 2r Packing = 52.4% Body Centered (BCC) Z = 2 | √3a = 4r Packing = 68.0% Face Centered (FCC/CCP) Z = 4 | √2a = 4r Packing = 74.0% ⚡ Remember: ‘Z’ is the Effective Number of Atoms. Corners = 1/8, Faces = 1/2, Body Center = 1, Edges = 1/4. Void Locations in an FCC Lattice (Z = 4 Atoms) Tetrahedral Voids (TV) = 2N Located at 1/4 distance along Body Diagonals. In FCC (N=4), there are 8 TVs. Octahedral Voids (OV) = N Located at Body Center (1) + Edge Centers (12×1/4 = 3). In FCC (N=4), there are 4 OVs. Density of a Unit Cell (The Most Important Solid State Formula) d = ( Z × M ) / ( a³ × NA ) • d = Density of the crystal (g/cm³) • Z = Effective number of atoms per unit cell • M = Molar Mass (g/mol) • a = Edge Length (Convert pm to cm!) 🚨 JEE Conversion Trap: 1 pm = 10⁻¹⁰ cm. So if a = 400 pm, a³ = (400 × 10⁻¹⁰)³ = 64 × 10⁻²⁴ cm³! 1. Schottky Defect (Missing Pairs) + – + – – + + – + – • Equal cations & anions missing. • Density DECREASES! • Found in NaCl, KCl, AgBr (high C.N.) 2. Frenkel Defect (Interstitial Dislocation) + – – – + + – + + – + – • Smaller ion (cation) moves to void. • Density remains SAME! • Found in ZnS, AgCl, AgBr (low C.N.)
Packing Fraction (FCC/HCP)
74.0% (Most Efficient)
Coordination Number = 12
F-Center Defect
Trapped Electron
Imparts Color (NaCl is Yellow)
Bragg’s Equation
nλ = 2d sin(θ)
Used for X-Ray diffraction
AgBr Exception
Both Defects!
Shows both Schottky & Frenkel defects
🌫️ Adsorption & Colloids. Select a Concept:
1. Physisorption Isobar (Const Pressure) x/m Temp (T) → • Weak Van der Waals forces. • Reversible & Multi-layered. • Decreases continuously with T. • Low Enthalpy (-20 to -40 kJ/mol) 2. Chemisorption Isobar x/m Temp (T) → Activation Energy Bump • Strong Chemical bonds. • Irreversible & Uni-layered. • Increases then decreases. • High Enthalpy (-80 to -240 kJ/mol) Freundlich Adsorption Isotherm: x/m = k P1/n log (x/m) log P → y-int = log k Slope = 1/n Logarithmic Form (y = mx + c) log(x/m) = (1/n) log P + log k • At Low Pressure: x/m ∝ P¹ (Linear) • At High Pressure: x/m ∝ P⁰ (Independent!) Note: ‘x’ is mass of adsorbate gas, ‘m’ is mass of adsorbent solid. The value of 1/n is between 0 and 1. Colloidal Solutions & The Tyndall Effect True Solution (< 1 nm) Colloidal Sol (1 – 1000 nm) Tyndall Cone (Optical Property) • Particles in a colloid are large enough (~1 nm to 1000 nm) to scatter a beam of visible light, making the path visible. Brownian Motion (Kinetic Property) • Continuous zig-zag motion of particles due to unequal bombardment by dispersion medium molecules. Resists gravity! Hardy-Schulze Rule (Coagulation of Colloids) Coagulating (flocculating) power depends on the valency of the oppositely charged active ion. For a Positive Sol (e.g., Fe(OH)₃) Needs Negative ions to coagulate. [Fe(CN)₆]⁴⁻ > PO₄³⁻ > SO₄²⁻ > Cl⁻ For a Negative Sol (e.g., As₂S₃) Needs Positive ions to coagulate. Al³⁺ > Ba²⁺ > Na⁺ ⚡ Gold Number Rule: Lower Gold Number = HIGHER Protective Power of a Lyophilic colloid (e.g., Gelatin = 0.005, highly protective)!
Lyophilic vs Lyophobic
Solvent-Loving vs Hating
Lyophilic is highly stable & reversible.
Electrophoresis
Movement under Electric Field
Determines charge on colloidal particle.
Peptization
Precipitate → Colloid
Adding an electrolyte to a fresh precipitate.
Emulsions
Liquid dispersed in Liquid
Milk (Oil in Water), Butter (Water in Oil).
🔥 High-Yield JEE Materials Trap:
In Zinc Blende (ZnS), S²⁻ forms the FCC lattice and Zn²⁺ occupies exactly half of the Alternate Tetrahedral Voids. In Fluorite (CaF₂), Ca²⁺ forms the FCC lattice and F⁻ occupies ALL the Tetrahedral Voids (C.N. is 8:4)!
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