Chemistry · Ch 3 — Some Analytical Techniques
Solvent Extraction
Solvent Extraction
The Idea Behind Solvent Extraction
When an organic substance is dissolved in an aqueous (water-based) solution, it can be pulled out of that solution by shaking the mixture with an organic solvent in which the substance is more soluble than it is in water. For this to work, the organic solvent must be immiscible with water, so that on shaking and settling, two distinct layers form. In this process, the solute distributes itself between the two immiscible liquids, and because it is more soluble in the organic layer, most of it transfers out of the aqueous phase and into the organic phase — this transfer happens purely because of the difference in the compound's solubility in the two liquids. Shaking the aqueous layer a few times with successive small volumes of fresh organic solvent extracts most of the solute; the organic solvent is then removed from the extract by distillation, leaving the recovered solute behind.
Why It's Useful, and Continuous Extraction …
What this figure shows. Two immiscible liquid layers are shown in contact after shaking together an aqueous solution containing the organic solute and an organic extracting solvent, illustrating the solute distributing itself between the aqueous phase and the (denser or lighter, depending on the solvent) organic phase, with more of the solute ending up in the organic layer because it is more soluble there; the apparatus typically used for this shaking/separating step is a separating funnel, though the source text names only the shaking process and immiscible-layer outcome, not the specific glassware, so the separating-funnel identi …