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🧪 Chemistry  ·  Surface Chemistry  ·  NEET & JEE

Why does soap form micelles only above a certain concentration, called the critical micelle concentration?

Answer: Above this concentration, soap molecules aggregate with hydrophobic tails inward to minimize contact with water.

  • A Below this concentration, soap molecules are largely insoluble in water in typical laboratory settings under usual circumstances
  • B Above this concentration, soap molecules aggregate with hydrophobic tails inward to minimize contact with water
  • C Soap molecules are said to form micelles mainly when dissolved in organic solvents according to most researchers
  • D Micelle formation is said to depend mainly on very high temperature, not concentration in the majority of cases studied

Correct answer: B. Above this concentration, soap molecules aggregate with hydrophobic tails inward to minimize contact with water

Explanation: Above the critical micelle concentration, surfactant molecules cluster together so their hydrophobic tails face inward, away from water, forming a stable micelle.

Adsorption Isotherm: x/m vs PressureP (pressure)x/mlow P: x/m ∝ Phigh P: saturation plateauAt high pressure, all surface sites are occupied - the curve flattens (monolayer saturation)

A typical adsorption isotherm: x/m (mass adsorbed per gram of adsorbent) rises steeply at low pressure, then flattens into a saturation plateau as the adsorbent surface fills up.

Concept context

Explore the chemistry that happens at interfaces, from catalysts that speed up industrial reactions to colloids like milk, smoke, and gels that surround us every day.

Read the full Surface Chemistry notes →