What can I do if I don't get a phase separation between my organic and water phases? Solvent extraction in a separation funnel is a very common method in preparative organic chemistry. But sometimes you don't get a nice phase separation between the organic and the water phase. 

What are the possible causes that can prevent the formation of two distinct phases, and how can you force a phase separation when you encounter such situations?
One such cause, where separation does not take place is the nature of the organic solvent. Its better to check the miscibility of the solvent with water. There are several websites, where one can get this info. For example 1 and 2.

Even with hydrophobic solvent, if the problem persists, one can add NaCl and then check the separation.