Question

23-1.If you are extracting a substance from water into ether, is it more effective to do one extraction with of ether or three extractions with ?

Short answer

When a substance gets extracted from water into ether, we could determine whether it is more effective to do one extraction with 300mL of ether or three extractions with 100mL of ether.

Step-by-step solution

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• Here, let us extract the substance from water by using either as a solvent.
• This process is done while using either as a solvent as that substance is considered to be more soluble in organic solvent.

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• If we have ever done with such kind of extraction before, we would have known that with first extraction and even with the second one, there is still some substance left in the solvent which we leave in the separatory funnel.
• It is to be noted that we leave it intentionally because we don’t want the water (contains impurities + substance) to drop in our beaker with pure solvent + substance.

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• Let us imagine that with first extraction we extracted 95% of our substance from water and there is still 5% of it left in the water.
• When the process gets repeated once again, we would extract 95% from those 5% left in the water so we would get a total of $0.95\times 5\%=4.75\%$ (now there is a 0.25 % of the substance left in the water).
• When the process gets repeated again, we would get $0.95\times 0.25\%=0.2375\%$ .
• Finally, we would have a total of (95 + 4.75 + 0.2375)%R=99.99% extracted substance.

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• Hence, it would be better to do three extractions with 100mLthan one with 300mL.
• It is to be noted that the volume is almost irrelevant when doing extractions.

Result:

Thus, it would be better to do three extractions with 100mL than one with 300mL.