I was asked to explain how different factors affect surface tension. I can understand how temperature plays a role. 1) Contamination: Increase in contamination decreases surface tension. I tried thinking about it.I thought maybe the particles that contaminate the fluid get in the way and don't allow the fluid particles to attract each as much as they usually do?( forgive me if that is terribly wrong). 2) Solutes: Highly soluble substances increase the surface tension. I can't think of anything. For sparingly soluble substances, the same analogy of contaminants could possible be used to decrease surface tension. Could someone help me understand the reasons?