In lab the other day we did an acid/base extraction to separate mixtures. The top layer of the mixture is the organic layer, which consists of diethyl ether and fluorine. The bottom layer is considered to be the aqueous layer, which consists of water and benzoate anion.
The different compounds have different polarities, my questions is: what is the reason we can separate compounds of different solubility, is because the solutions are insoluble in each other?
And then when choosing specific solvents for an extraction, what is the reason for choosing them? Is it again because of the fact that different molecules have different densities and mix or don't mix well with other solvents?
Thanks for the help!
The reason we can separate compounds of different solubility in an acid/base extraction is indeed because they are insoluble in each other. In this technique, we exploit the differences in polarity and solubility between the organic and aqueous layers.
When we have a mixture of compounds with different solubilities, they will distribute themselves between the organic and aqueous layers based on their affinity for each solvent. Compounds that are more polar and water-soluble will remain in the aqueous layer, while less polar and organic-soluble compounds will preferentially dissolve in the organic layer.
In the specific case you mentioned, diethyl ether is a nonpolar organic solvent, and fluorine is a nonpolar molecule, so they will dissolve well in each other, forming the organic layer. On the other hand, water is a polar solvent, and the benzoate anion is a polar molecule due to the presence of charged groups, so they will mostly remain in the aqueous layer.
Now, when it comes to choosing specific solvents for an extraction, several factors need to be considered:
1. Solubility: The compound to be extracted should have a significantly different solubility in the chosen solvents. This difference allows for efficient separation.
2. Selectivity: The solvent should selectively dissolve the target compound while minimizing the extraction of unwanted impurities. This selectivity can depend on various factors, such as polarity, functional groups, and the size of the molecules.
3. Density: While density can play a role in separations involving immiscible liquids, such as in the case of your acid/base extraction, it is not the primary consideration. In these extractions, the organic and aqueous solvents are typically chosen based on their compatibility with the target compounds rather than their density differences.
4. Safety and environmental concerns: Solvents that are hazardous, toxic, or environmentally harmful should be avoided whenever possible. It is preferable to choose solvents that are relatively safe to handle and dispose of.
In summary, the choice of solvents for extraction is primarily based on the differential solubilities of the compounds to be separated. The solvents should have distinct affinities and selective properties to effectively partition the compounds between the organic and aqueous layers.