Show that multi step solvent extraction is more efficient than single step extraction.
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This is because when a large batch of solvent is used to extract a product, only around 30% of the product will be extracted and 70% of the extract will still remain in the original sample. If it is a single-step extraction, then 70% of the extract will get wasted.
However, if it is a multi-step extraction method, another batch of the solvent is added so that more extract can be got from the original sample.
Although, it may not be economical and may need more effort, the efficiency of a multi-step solvent extraction method is more preferable when you need quality products without much wastage.
2 answers · Chemistry
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Transferring a solute from one solvent into another is called Extraction, or more precisely, liquid-liquid extraction. The solute is extracted from one solvent into the other because the solute is more soluble in the second solvent than in the first. When a solution (solute A in solvent 1) is shaken with a second solvent (solvent 2) with which it is not miscible the solute distributes itself between the two liquid phases. When the two phases have separated again into two distinct solvent layers, and equilibrium will be achieved such that the ratio of the concentrations of the solute in each layer is defined by a constant. The constant, called the distribution coefficient (or partition coefficient) K, is defined by
K = C2/C1
where C1 and C2 are the concentrations at equilibrium, in grams per liter (or milligrams per milliliter) of solute A in solvent 1 and in solvent 2, respectively. This relationship is a ratio of two concentrations and is independent of the actual amounts of the two solvents mixed. The distribution coefficient has a constant value for each solute considered and depends on the nature of the solvent used in each case.
Every time an extraction is carried there will be mass transfer of solute from solvent 1 to solvent 2.
The solute will distribute itself in the two liquid phases and a new equlibrium will be estblished
to achieve K - the partition coefficient which is constant
Therefore multiple small extractions that generate multiple equilibrium stages of mass transfer of solute are more efficient than a single extraction which involves a single equilibrium stage of mass transfer of solute . Considering the fact that the partition coefficient of solute between the two solvents is independent of the quantity of solvent being used for extraction a large volume of solvent in a single extraction is just adding cost without any value addition