Question

Why surface tension of soap solution is less than pure water?

Answer 1

One other problem with pure water bubbles is evaporation: the surface quickly becomes thin, causing them to pop. ... Since the surface tension forces become smaller as the distance between water molecules increases, the intervening soap molecules decrease the surface tension.

Answer 2

surface tension of soap solution is less than pure water because pure water have no impurity and behave as strong streched strong bond but when soap is added the bond become loose due to presence of stiarate ion and hydrogen ion .