Organic compounds in aqueous sample A will be extracted using liquid-liquid extraction. Which of the following is the most appropriate solvent to use?

• A. Methanol
• B. Water
• C. Hexane
• D. Hydrochloric acid solution

Answer: (C)

Liquid-liquid extraction relies on how much of the organic compound prefers an immiscible organic solvent over water. For organic compounds in an aqueous sample, you want a solvent that is nonpolar enough to dissolve those compounds but completely separate from water. Hexane fits perfectly: it’s nonpolar and immiscible with water, so it forms its own organic layer that can effectively pull nonpolar organics out of the aqueous phase. Many organic compounds dissolve well in hexane, making the distribution into the organic phase favorable.

In contrast, methanol is polar and mixes with water, so it won’t form a distinct extractive phase. Water remains the same phase as the sample, not providing extraction. Hydrochloric acid solution is also aqueous and would not serve as an organic solvent to carry nonpolar organics into a separate layer. Thus hexane is the best choice for this liquid-liquid extraction.