[trinhn812]

An emulsion sometimes forms between the organic and aqueous layers during extraction.
An emulsion is a mixture of two immiscible liquids (many oil/water mixtures are emulsions,
think vinaigrette salad dressings). If this happens, the addition of aqueous sodium chloride
can help to “break” the emulsion and facilitate the separation of the two layers. How does
the addition of sodium chloride help in this regard?

I don't understand how sodium chloride would help

[dunno260]

From my understanding you get two things working in your favor.  You are upping the ionic strength of the organic phase making the emulsion much less stable (and interupting any hydrogen bonding helping hold the emulsion together).  In addition, a saturated solution of NaCl (brine) is much more dense and that can also help in the seperation from solvents that are less dense than water (most all of them but chloroform, dichloromethane).  However, I would go with the former as being the more likely since the addition of a little NaCl which would have a negligible change on the density often will begin to get the phases to fully separate.