[anishd]

When separating phenol from aniline, we use a strong base to separate the phebol and a strong acid to separate the aniline. Any thoughts as to why?

[Mandeep Deka]

Phenol being a strong acid reacts with the strong base to form a salt which can be expected to get precipitated. Something the same for aniline as well!!

[g-bones]

Phenols have a convenient pH of about 11 which means they can be deprotonated by a typical "workup" solution like NaOH (pKa of water is 15.7).  Aniline on the other hand has a pKa of about 30 (in DMSO) which is not appropriate for deprotonation by a typical base like hydroxide.  In addition, nitrogen is much more basic in nature than oxygen (the result of a difference in electronegativity) so protonation of aniline to form the positively charged species is much easier with a typical HCl solution. 

Hope this helps.

[mcdonabe]

To expound upon g-bones' point of electronegativity, oxygen is more stable with a negative charge due to electronegativity, so it then follows that the pka of phenol is lower than aniline, since pka is representative of the stability of the anion resulting in from deprotonation. As a side note, phenol is not a strong acid..