What is the role of soap in this emulsion?

Question

Compare the stability of the water-benzene emulsions prepared with and without the addition of soap solution.

Answer 1

Water-benzene become more stable with the soap. The water-benzene form an emulsion of separate layers since water is polar and benzene is non-polar. Soap acts as an emulsifier so that they combine. Soap molecules have 2 ends one hydrophobic that attracts the benzene molecule and the other hydrophilic that attracts the water molecule. Soap allows the benzene-water layers to mix and form a single-phase mixture.

Answer 2

The subject of forming emulsions and the application of a "soap" better called a surfactant or emulsifier is a vast one. Briefly oils and many organic compounds including benzene are immiscible with water. The organic compound is broadly said to be hydrophobic. If an attempt is made to form a homogeneous mixture of say benzene in water, vigorous stirring or agitation will result in a milky liquid that soon separates into a water and a benzene phase. The hydrophobic benzene micro-drops soon coalesce and come out of solution.

However, if a surfactant is added it is possible to form a stable emulsion. Simply explained, the surfactant molecule has a hydrophobic end and a hydrophylic end. The hydrophobic end is able to join with the benzene micro-drop and produce a protective shell around it. This leaves a hydrophylic surface on the benzene micro-drop which is fully compatible with the water phase. Due to the protective nature of he surfactant, the coalescing of the benzene is prevented and the colloidal emulsion reains stable.

This is what happens in the question you have asked.

Maybe you do not know some words: hydrophobic means "water hating" and hydrophylic eans "water loving"