Brine Solutions in Extractions

[justadream]

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In an extraction, why does adding a salt (forming a brine solution) increase the differences between two liquid layers (one aq, one organic)?

 

[JMMTB]

The reason why the two layers separate is due to polarity. Aq is extremely polar with all the H-bonding that can occur. Sometimes your organic layer can form hydrogen bonds (phenol or benzoic acid in CH2Cl2) this forms an emulsion or mixing of the two layers where they meet. When you add brine you increase the polarity of the Aq layer because of the addition of all the ions.