The Soap as an Emulsifier

Explain that soap, water and oil together form an emulsion with the soap acting as an emulsifier

Emulsion – is the dispersion of small droplets of one liquid within another liquid.

Ex. soap + water + oil

Emulsifier – a substance which allows the initially immiscible substances to be miscible with each other

Ex. soap

Soap as an emulsifier:

  • When oil and water are mixed together, no interaction will occur and two distinct layers will be observed since oil is non polar and the water is polar.
  • However, a cloudy layer is observed between the oil and water layers when soap is added as a result of emulsion.
  • The hydrophobic tail of the soap molecules interact with the oil molecules, causing the oil molecule to break into smaller droplets (micelles) which are suspended in water and seen in cloudy layer.

Note: Oil micelles do not clump together since the anionic heads of adjacent soap molecules forms repulsion towards each other (electrostatic attraction).