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Differential Extraction Using a Separating Funnel

Chemistry · General Principles Of Organic Chemistry · NEET

Differential extraction means shaking a water-based mixture with an immiscible organic solvent in a separating funnel, so the compound moves into the solvent layer in which it dissolves better. The two liquids form two clear layers, and you run off the lower layer through the tap. Memory hook: "Like dissolves like, then let gravity split the two layers."
Differential Extraction in a Separating FunnelOrganic solvent layer(holds the compound)Water layer (aqueous)Tap: run off lower layer firstRule: like dissolves like1. Shake aqueous mix with an immiscible solvent2. Let two layers settle3. Drain lower layer via tap4. Remove solvent to get pure compound
The compound moves into the immiscible organic solvent because it is more soluble there; the two layers separate by density and the lower one is drained through the tap.

Your doubts, answered

What is differential extraction and when is it used?

It is used when an organic compound is dissolved in water (an aqueous medium). You shake this aqueous solution with an organic solvent in which the compound is more soluble than in water. The compound moves into the organic layer, which you then separate. Later the solvent is removed by distillation or evaporation to get the pure compound back.

Why must the two solvents be immiscible?

If they mixed together they would form one single liquid and never split into layers, so you could not separate them. Being immiscible means water and the organic solvent stay as two distinct layers (like oil and water). Only then can the separating funnel drain one layer away from the other.

Which layer comes out first from the separating funnel?

The lower layer always comes out first through the stopcock (tap) at the bottom. The layer that sits at the bottom is the denser liquid. For example, if the organic solvent is denser than water it forms the lower layer; if it is lighter it stays on top and is poured out from the mouth.

What is continuous extraction and why is it needed?

If the organic compound is only slightly more soluble in the organic solvent, one shake extracts very little, and you would need a huge amount of solvent. Continuous extraction solves this by using the same small amount of solvent again and again in a loop to slowly pull out the compound. NCERT lists it as an extension of differential extraction.

How is differential extraction different from distillation?

Distillation separates liquids using differences in boiling point (heating and condensing). Differential extraction separates using differences in solubility between two immiscible liquids at room temperature, no boiling of the mixture needed. Extraction is chosen when the compound is dissolved in water and would be hard to distil out.

⚠️ The NEET trap
✗ The compound moves into the organic solvent because that solvent has a higher boiling point.
✓ The compound moves into the organic solvent because it is MORE SOLUBLE in that solvent than in water (like dissolves like). Boiling point plays no role in the extraction step itself.
🧠 Extraction is decided by solubility, not boiling point. Boiling point only matters later when you remove the solvent.

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Frequently asked

Is a separating funnel and a separatory funnel the same thing?

Yes. NCERT uses both terms. It is a pear-shaped glass funnel with a stopcock (tap) at the bottom used to separate two immiscible liquid layers.

Give a common NEET example of differential extraction.

Separating an organic compound dissolved in water by shaking with ether or benzene. Also, in steam distillation the collected distillate of water and organic liquid (like aniline) is finally separated using a separating funnel, which is a differential extraction step.

Why do we shake the funnel before letting it settle?

Shaking increases contact between the two liquids so the compound quickly redistributes into the layer where it is more soluble. After shaking you let it stand so the two immiscible layers settle and become sharp.

Does differential extraction give a pure compound directly?

No. You first get the compound dissolved in the organic solvent. The pure compound is obtained only after removing that solvent by distillation or evaporation.

Related concepts:
Chromatography: Principle and TypesSteam Distillation and Its PrincipleSimple and Fractional DistillationCrystallisation for Purifying Organic SolidsSublimation as a Purification Technique
Practise Chemistry for NEET:
Chemistry MCQs (free, chapter-wise)General Principles Of Organic Chemistry PYQs