Question

Which of the following would be the best procedure for extracting acetaldehyde from an aqueous solution? a. A single extraction with \(100 \mathrm{mL}\) of ether b. Two successive extractions with \(50 \mathrm{mL}\) portions of ether c. Three successive extractions with \(33.3 \mathrm{mL}\) portions of ether d. Four successive extractions with \(25 \mathrm{mL}\) portions of ether

Short answer

d. Four successive extractions with 25 mL portions of ether

Step-by-step solution

- Understanding Extraction

Extraction is the process of separating a substance from a mixture by dissolving it in a suitable solvent. Repeated extractions with smaller volumes of solvent are usually more effective than a single extraction with a larger volume.

- Comparing Single vs. Multiple Extractions

Analyze the efficiency of extracting acetaldehyde using one large volume of ether versus multiple smaller volumes. When the same total volume is used, multiple extractions are more thorough due to the repeated partitioning of the solute.

- Applying Distribution Law

According to the partition coefficient, the solute distributes itself between the two immiscible solvents (water and ether). Multiple smaller volume extractions leverage this distribution more effectively than one large volume extraction.

- Evaluating Each Option

Evaluate each provided method: - Option a: Single extraction with 100 mL ether may leave a significant amount of acetaldehyde in the aqueous phase. - Option b: Two extractions with 50 mL portions are better but may still not fully extract acetaldehyde. - Option c: Three extractions with 33.3 mL portions are even better. - Option d: Four extractions with 25 mL portions maximize the removal of acetaldehyde.

- Conclusion

By the principles of extraction, multiple, successive smaller-volume extractions are most efficient. Thus, four successive extractions with 25 mL portions of ether would be the best option.

Key concepts

multiple extraction efficiency

In organic chemistry, when separating compounds from mixtures, multiple extraction is a key technique for enhancing efficiency. Rather than using a single, large volume of solvent, it is often more effective to use several smaller volumes. This is because each extraction step helps remove more of the substance from the aqueous solution. Think of it as multiple opportunities for the substance to get partitioned into the organic layer. This step-by-step separation process maximizes the overall extraction yield.
Each successive extraction with fresh solvent taps into the decreasing concentration of the solute, ensuring that more of the target compound is collected.

partition coefficient

The partition coefficient, represented as \((K_d)\), plays a crucial role in the extraction process. It signifies how a substance distributes between two immiscible solvents. In the exercise, acetaldehyde distributes between water (the aqueous phase) and ether (the organic phase). A higher partition coefficient means that the compound has a higher tendency to move into the organic phase (ether in this case).
Mathematically, the partition coefficient is given by \[K_d = \frac{[solute]_{organic}}{[solute]_{aqueous}} \]. By leveraging this coefficient, multiple smaller volume extractions prove more efficient because they exploit this repeated solute distribution, effectively reducing the quantity left in the water each time.

solvent extraction process

Solvent extraction process is a widely used method in organic chemistry for separating compounds based on their solubility. This involves dissolving a mixture into two immiscible liquids, usually one organic and one aqueous.
In the given exercise, ether acts as the organic solvent, while water is the aqueous solvent. The key goal is to transfer acetaldehyde from the water phase into the ether phase. By implementing four successive extractions with smaller portions of ether, the process maximizes the transference due to the principle of repeating partitioning steps. Over multiple extractions, the cumulative effect is a more thorough removal of the desired compound.

aqueous solution separation

Aqueous solution separation involves isolating a solute from an aqueous mixture. When extracting acetaldehyde from its aqueous solution using ether, each step gradually depletes the concentration of the solute in the water.
Imagine this like wringing out a wet sponge. Each squeeze (extraction) removes a portion of the water, but by repeatedly squeezing (multiple extractions), you can get out significantly more water compared to one big squeeze. This analogy fits the exercise, where successive extractions with smaller portions of ether are recommended. They incrementally draw out more acetaldehyde into the organic layer, making the separation more efficient.