Adsorption Types:

Colloid Particle Size: True solution < 1 nm < Colloid < 1000 nm < Suspension

Colloidal Properties: Tyndall (light scattering) | Brownian (molecular bombardment) | Electrophoresis (charged, migrates in E-field) | Coagulation (charge neutralized → settles)

Lyophilic vs. Lyophobic:

• Lyophilic (starch, gelatin, proteins, gum): stable, reversible, self-stabilizing, needs large electrolyte to coagulate
• Lyophobic (Au sol, $As_{2}S_{3}$, Fe(OH)_{3}): unstable, irreversible, needs stabilizer, small electrolyte coagulates

Hardy-Schulze: For $As_{2}S_{3}$ (−ve): $Al^{3+}$ > $Ba^{2+}$ > $Na^{+}$ | For Fe(OH){3} (+ve): [Fe(CN){6}]^{4-} > $SO_{4}^{2-}$ > $Cl^{-}$

Gold Number: Lower = Better. Gelatin 0.005 > Albumin 0.1 > Starch 25

Emulsions: O/W (milk, vanishing cream) ← mixes with water → W/O (butter, cold cream)

Industrial Catalysts: Haber = Fe | Contact = $V_{2}O_{5}$ | Ostwald = Pt | Hydrogenation = Ni/Pd

Selectivity (CO + $H_{2}$): ZnO-$Cr_{2}O_{3}$ → $CH_{3}OH$ | Cu → HCHO | Ni → $CH_{4}$

Preparation Methods: Reduction (Au sol) | Hydrolysis (Fe(OH)_{3}) | Bredig's arc (metals) | Peptization (precipitate → colloid)

Purification: Dialysis | Electrodialysis | Ultrafiltration