The principle involved in paper chromatography is
- A.Absorption
- B.Partition
- C.Solubility
- D.Volatility
Correct answer
Explanation
The correct answer is B, Partition. Paper chromatography separates substances because each one divides, or partitions, itself differently between two liquid phases.
In paper chromatography the stationary phase is the water held in the cellulose fibres of the paper, and the mobile phase is the solvent that rises up the paper by capillary action. As the solvent moves, each component of a mixture keeps distributing itself between the bound water and the moving solvent. A component that prefers the solvent travels farther, while one that prefers the stationary water lags behind, so the mixture spreads into separate spots. Each spot is identified by its Rf value, the distance it travels divided by the distance the solvent front travels. A common school example is separating the dyes in black ink.
A is wrong: separation by adsorption onto a solid surface is the basis of column and thin-layer chromatography, and absorption is not the principle at all.
C is wrong: solubility plays a part, but the working principle is the partition between two phases.
D is wrong: separation by volatility is used in gas chromatography and distillation, not in paper chromatography.
Exam tip: Paper chromatography = partition; column and TLC = adsorption; Rf = distance of spot ÷ distance of solvent front.
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