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Difficulty: HardSeparating Funnel and Solvent Extraction

An organic solute XX dissolved in an aqueous solution is to be extracted using ethoxyethane (diethyl ether, density=0.71 g/cm3\text{density} = 0.71\text{ g/cm}^3, boiling point=34.6∘C\text{boiling point} = 34.6^\circ\text{C}). Which of the following statements correctly identifies the essential properties of ethoxyethane for this process and the location of the organic layer in the separating funnel?

  1. Ethoxyethane must be immiscible with water, have a higher solubility for solute XX than water, and form the upper layer because its density is less than that of water.Answer
  2. B
    Ethoxyethane must be miscible with water, have a higher solubility for solute XX than water, and form the lower layer because its boiling point is lower than that of water.
  3. C
    Ethoxyethane must be immiscible with water, have a lower solubility for solute XX than water, and form the lower layer because its lower boiling point causes it to sink.
  4. D
    Ethoxyethane must react chemically with water, dissolve solute XX sparingly, and form the upper layer because of its higher vapor pressure.

Answer

Ethoxyethane must be immiscible with water, have a higher solubility for solute XX than water, and form the upper layer because its density is less than that of water.
Solvent extraction using a separating funnel relies on three key principles: the organic solvent must be immiscible with water, the solute must be preferentially more soluble in the organic solvent than in water, and the relative density determines layer placement. Since ethoxyethane has a density (0.71 g/cm30.71\text{ g/cm}^3) lower than that of water (1.00 g/cm31.00\text{ g/cm}^3), it forms the less dense upper layer.

Step-by-Step Solution

1
Identify the requirement for liquid-liquid separation in a separating funnel.
The extraction solvent must be immiscible with the original solvent (water) so that two distinct liquid phases form.
If the two liquids are miscible, they form a single homogeneous solution and cannot be physically separated using a tap funnel.
2
Determine the solubility criterion (distribution ratio) for effective extraction.
The target solute XX must be significantly more soluble in the extracting organic solvent than in water.
Solvent extraction relies on preferential partitioning (distribution) of the solute into the organic layer upon shaking.
3
Evaluate the layer positioning based on physical properties.
Because ethoxyethane has a lower density (0.71 g/cm30.71\text{ g/cm}^3) than water (1.00 g/cm31.00\text{ g/cm}^3), it floats on top to form the upper layer.
Layering in a separating funnel is determined exclusively by relative density, not by boiling point or vapor pressure.

Key Concept

Principles of Solvent Extraction and Density Layering in a Separating Funnel
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Topics

Separating Funnel and Solvent Extraction

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