Question

Which of the following increases the efficiency of liquid-liquid extraction?

• A. Multiple extractions with small volumes of solvent
• B. Using the same solvent multiple times
• C. Increasing the temperature excessively
• D. Using highly miscible solvents

Hint:

In extractions, always opt for multiple small-volume extractions instead of a single large one — it increases recovery of the solute due to better partitioning.

Answer 1

The Correct Option is A

Liquid-liquid extraction is a technique used to separate compounds based on their relative solubilities in two immiscible liquids, typically an aqueous phase and an organic phase.
The efficiency of this process depends on how effectively the solute partitions between the two layers.
Instead of extracting once with a large volume of solvent, it is much more efficient to perform multiple extractions with smaller volumes.
This is because each small extraction removes a portion of the solute, and the repeated process ensures more of the solute is transferred to the extracting phase.
This principle is based on the distribution law and is mathematically supported by the decreasing exponential nature of remaining solute after each extraction.
For example, extracting with 3 portions of 10 mL each is significantly more effective than extracting once with 30 mL, assuming all else is equal.
Other options are less efficient or counterproductive:
- Using the same solvent multiple times is essentially a single extraction if combined.
- Increasing the temperature excessively can change solubility patterns unpredictably.
- Using highly miscible solvents defeats the purpose of having two separate immiscible phases.
Therefore, the most effective method is: Multiple extractions with small volumes of solvent.