Differential Extraction
Differential Extraction, explained for NEET
Two failure modes account for most lost marks here, and the dossier names both. The first is picking a solvent that dissolves in water. Shake an aqueous solution with ethanol and you get one homogeneous liquid, not two layers — there is nothing to separate, and the whole method collapses. The second is assuming the organic layer sits on top. It sits wherever its density puts it: ether floats, chloroform sinks.
Differential extraction separates an organic compound from an aqueous solution using its unequal solubility in two immiscible liquids. NCERT Class 11 Chemistry, Chapter 8, page 281 states the requirement plainly: the organic solvent must be immiscible with water, and the compound must be more soluble in that solvent than in water. Shake the two in a separating funnel, let them settle, and the compound distributes itself between the layers in favour of the one it prefers.
Two consequences follow. One extraction is never complete — some compound stays behind in the aqueous layer every time. Repeated extraction with small volumes recovers more than a single extraction with the same total volume, because each fresh portion of solvent re-establishes the distribution. And when the compound is only sparingly soluble in the organic solvent, batch shaking is too inefficient to bother with; continuous extraction recycles the same solvent through the aqueous solution over hours. NCERT page 281 covers this case.
The separating funnel itself (NCERT page 282) is drained from the bottom, so you run the lower layer out first regardless of which layer you want. Identify the layers by density before you open the stopcock, not after.
For NEET this is a low-frequency, high-certainty topic: roughly one question every five years, almost always recall or a one-step interpretation. Watch out for options naming a water-miscible solvent, and for any option that fixes the organic layer as the upper one.
Can you answer these Differential Extraction MCQs?
Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.
Differential extraction separates an organic compound from an aqueous solution by exploiting:
Show answer and why every option is right or wrong
Answer: D. The method rests on the compound dissolving to different extents in water and in an immiscible organic solvent, as stated in NCERT Class 11 Chemistry, Chapter 8, page 281.
Why A is wrong: A is wrong because a boiling-point difference is what distillation exploits; extraction is carried out at room temperature and no phase change occurs.
Why B is wrong: B is wrong because melting-point differences are not used to separate compounds; melting point serves as a purity criterion after separation.
Why C is wrong: C is wrong because differential adsorption on a solid is the basis of adsorption chromatography, a different technique in the same chapter.
An organic compound dissolved in water is to be extracted into an organic solvent. The essential requirement on that solvent is that it must be:
Show answer and why every option is right or wrong
Answer: A. Two distinct layers must form for any separation to be possible, and the compound must prefer the organic layer; NCERT Class 11 Chemistry, Chapter 8, page 281 gives both conditions together.
Why B is wrong: B is wrong because density decides only which layer sits on top; both a denser solvent like chloroform and a lighter one like ether work equally well.
Why C is wrong: C is wrong because a water-miscible solvent such as ethanol gives one homogeneous liquid — no interface forms and nothing can be separated.
Why D is wrong: D is wrong because boiling point matters only later, when the solvent is evaporated off to recover the compound, not for the extraction step itself.
An aqueous solution of an organic compound is shaken with diethyl ether in a separating funnel and the layers are allowed to settle. The organic compound is found:
Show answer and why every option is right or wrong
Answer: B. The compound distributes itself between the two immiscible layers in favour of the one in which it is more soluble, so a residue always stays behind in water; NCERT Class 11 Chemistry, Chapter 8, page 281.
Why A is wrong: A is wrong because a single extraction is never complete — some compound remains in the aqueous layer every time, which is precisely why the extraction is repeated.
Why C is wrong: C is wrong because the compound is chosen to be more soluble in the organic solvent; that preference is the whole basis of the method.
Why D is wrong: D is wrong because an equal split would occur only by coincidence; the distribution follows the relative solubilities, not a fixed ratio.
A student extracting an aqueous solution with chloroform opens the stopcock of the separating funnel and runs off the lower layer. That lower layer is:
Show answer and why every option is right or wrong
Answer: C. Position is fixed by density alone, and chloroform is denser than water, so it forms the lower layer, and the lower layer is the one run off first through the tap of the separating funnel (the funnel is shown in NCERT Class 11 Chemistry, Chapter 8, page 282).
Why A is wrong: A is wrong because water is not always the denser liquid — chloroform is denser than water and settles below it.
Why B is wrong: B is wrong because the organic layer has no fixed position; ether is less dense than water and forms the upper layer.
Why D is wrong: D is wrong because the order of addition has no effect; the liquids rearrange by density as soon as shaking stops.
An organic compound is only sparingly soluble in the organic solvent available. The technique used to recover it from its aqueous solution is:
Show answer and why every option is right or wrong
Answer: B. Sparing solubility makes batch shaking too inefficient, so the same solvent is circulated through the solution over a long period; NCERT Class 11 Chemistry, Chapter 8, page 281.
Why A is wrong: A is wrong because low solubility limits how much the solvent can take up per contact; more volume in one go recovers less than repeated fresh contact.
Why C is wrong: C is wrong because sublimation applies to solids that pass directly to vapour, and is a separate technique covered elsewhere in this unit.
Why D is wrong: D is wrong because steam distillation is a distillation method for volatile water-immiscible compounds, not an extraction from solution.
A fixed volume of organic solvent is available to extract a compound from its aqueous solution. Which use of that solvent recovers the most compound?
Show answer and why every option is right or wrong
Answer: A. Each extraction leaves some compound behind, so applying the distribution repeatedly with fresh portions removes more than one contact with the same total volume; this follows from the incomplete single extraction described in NCERT Class 11 Chemistry, Chapter 8, page 281.
Why B is wrong: B is wrong because one contact reaches a single distribution and stops; the residue it leaves in water is never recovered.
Why C is wrong: C is wrong because the result depends on how many times the distribution is re-established, not on the total volume alone.
Why D is wrong: D is wrong because solubility in water sets the distribution for each contact, but the number of contacts still determines the total recovered.
Four solvents are proposed for extracting an organic compound from an aqueous solution. Which one cannot be used?
Show answer and why every option is right or wrong
Answer: C. Ethanol is miscible with water, so no second layer forms and no separation is possible; the immiscibility requirement is given in NCERT Class 11 Chemistry, Chapter 8, page 281.
Why A is wrong: A is wrong because ether is immiscible with water and is the standard extraction solvent, forming the upper layer.
Why B is wrong: B is wrong because benzene is immiscible with water and forms a distinct upper layer.
Why D is wrong: D is wrong because chloroform is immiscible with water and forms a distinct lower layer.
After extracting a compound into ether and separating the layers, a student is left with an ether solution of the compound. To obtain the compound itself, the next step is to:
Show answer and why every option is right or wrong
Answer: D. The compound is recovered by removing the volatile solvent, which is why the extracting solvent is chosen to be low-boiling; NCERT Class 11 Chemistry, Chapter 8, page 281.
Why A is wrong: A is wrong because shaking with water reverses the extraction, sending part of the compound back into the aqueous layer.
Why B is wrong: B is wrong because the compound is dissolved in the ether, and cooling a dilute solution is not a reliable way to recover it — that is crystallisation, a different technique with its own solvent requirements.
Why C is wrong: C is wrong because adding a third solvent only dilutes the solution further; it removes nothing and creates a mixture that is harder to separate.
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How do you solve a Differential Extraction question? A worked example
- 1
Given
An aqueous solution containing an organic compound. Two solvents are on the bench: ethanol and chloroform. Density of chloroform = 1.49 g cm⁻³; density of water = 1.00 g cm⁻³ (both at room temperature).
- 2
Required
Which solvent can be used for differential extraction, and after shaking, which layer — upper or lower — holds the organic compound?
- 3
Concept
Differential extraction needs two immiscible liquids so that a distinct interface forms. The compound then distributes itself in favour of the liquid in which it is more soluble. Layer position is decided by density, independently of which layer carries the compound.
4. Relation used: No algebraic formula applies. Two qualitative relations do: (i) the solvent must be immiscible with water; (ii) the denser liquid forms the lower layer. - 5
Substitution
Ethanol is miscible with water in all proportions → no interface → rejected at once. Chloroform is immiscible with water → an interface forms → acceptable. Comparing densities: 1.49 g cm⁻³ > 1.00 g cm⁻³.
- 6
Calculation
Density difference = 1.49 − 1.00 = 0.49 g cm⁻³, with chloroform the denser. Chloroform therefore settles below the aqueous layer. The organic compound, being more soluble in chloroform than in water, is carried mainly into that lower layer. The densities here are measured quantities quoted to three and to three significant figures respectively; no exact constants enter this problem, and the comparison itself depends only on which value is larger, not on the precision of either.
- 7
Final answer
Chloroform is the usable solvent. The organic compound is found mainly in the lower layer, which is run out first through the stopcock of the separating funnel.
- 8
Common trap
Two traps sit in this single question, and the dossier names both. Rejecting ethanol on the grounds that "it is a poor solvent for organic compounds" reaches the right answer for the wrong reason — ethanol dissolves organic compounds well; it is disqualified because it is miscible with water. And answering "upper layer" out of habit is the second trap: the organic layer is upper with ether and lower with chloroform, so the layer must be decided from the density every time.
- 9
Similar NEET-style question
An organic compound in aqueous solution is shaken with diethyl ether (density 0.71 g cm⁻³) in a separating funnel. Which layer is run out first through the stopcock, and does it contain the bulk of the compound? *(Answer: the lower, aqueous layer is run out first — the funnel always drains from the bottom — and it does not hold the bulk of the compound, which is in the upper ether layer.)*
[provenance-pending] Source provenance not yet catalogued for CHE.U13.DIFFERENTIAL_EXTRACTION. NCERT citations, verified PYQs, and exam traps will appear here once the dossier is populated.
Sources
Page numbers are the ones printed in the current NCERT textbook (2023 rationalised edition), unless marked pre-2023. The books are free at ncert.nic.in.
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