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Surface Chemistry

Adsorption, catalysis, colloids and emulsions

Key Concepts
  • Adsorption: accumulation of substance on surface (adsorbate on adsorbent)
  • Physisorption: weak van der Waals forces; chemisorption: chemical bonds
  • Colloids: dispersed particles 1–1000 nm in size; show Tyndall effect
  • Coagulation: colloidal particles aggregate and settle
  • Catalysis: catalyst provides alternative pathway with lower activation energy
Important Formulae
Freundlich adsorption isotherm x/m = kP^(1/n), n ≥ 1
Langmuir adsorption isotherm x/m = abP / (1 + bP)
Quick Tips
  • Physisorption increases at low T; chemisorption increases at high T (up to a limit).
  • Sols: solid dispersed in liquid; gels: liquid dispersed in solid; emulsion: liquid in liquid.
  • Hardy-Schulze rule: higher valency of coagulating ion → more effective coagulation.
Sample Practice Questions

  1. Freundlich adsorption isotherm: x/m = kP^(1/n). At high pressure, adsorption becomes:

    • Zero
    • Constant (saturated)
    • Exponentially increasing
    • Inversely proportional to P
    Show answer

    Answer: Constant (saturated)

  2. Gold numbers measure the __ of a lyophilic colloid:

    • Charge
    • Protective ability
    • Particle size
    • Viscosity
    Show answer

    Answer: Protective ability

  3. Peptisation means:

    • Adding more solvent
    • Converting precipitate back to colloidal state by adding electrolyte
    • Coagulating a colloid
    • Filtering a colloid
    Show answer

    Answer: Converting precipitate back to colloidal state by adding electrolyte

  4. Adsorption is always:

    • Endothermic
    • Exothermic
    • Isothermal
    • Adiabatic
    Show answer

    Answer: Exothermic

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Practice Questions

Practice 20 randomly selected NEET questions on Surface Chemistry. Answers are revealed after each question.

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