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Zorluk: ZorPaper and Column Chromatography

A organic mixture containing naphthalene, chlorobenzene, acetophenone, and benzoic acid is separated using silica gel column chromatography with hexane (a non-polar solvent) as the mobile phase. Arrange these four compounds in order of their elution from the column, starting with the compound that elutes first and ending with the compound that elutes last.

  1. 1Naphthalene
  2. 2Chlorobenzene
  3. 3Acetophenone
  4. 4Benzoic acid

Cevap

The correct order of elution from first to last is: Naphthalene, Chlorobenzene, Acetophenone, Benzoic acid.
In silica gel column chromatography using a non-polar solvent like hexane, separation is governed by adsorption efficiency. Silica gel contains polar silanol groups (−Si−OH-Si-OH). Non-polar compounds (naphthalene) do not interact significantly with the polar stationary phase and dissolve readily in the non-polar eluent, causing them to move rapidly down the column and elute first. As solute polarity increases from weakly polar (chlorobenzene) to moderately polar ketone (acetophenone) to strongly polar hydrogen-bonding acid (benzoic acid), the strength of adsorption increases, delaying elution accordingly.

Adım Adım Çözüm

1
Identify the nature of the stationary and mobile phases.
The stationary phase (silica gel) is polar, while the mobile phase (hexane) is non-polar.
Normal-phase column chromatography relies on adsorption differences on a polar stationary matrix.
2
Determine the polarities of the four organic solutes based on their functional groups.
Naphthalene (non-polar hydrocarbon) < Chlorobenzene (weakly polar haloarene) < Acetophenone (moderately polar ketone) < Benzoic acid (strongly polar carboxylic acid).
Carboxylic acids can hydrogen-bond, ketones have strong dipoles, haloarenes have weak dipoles, and aromatic hydrocarbons are non-polar.
3
Correlate solute polarity with retention time and elution order.
Non-polar solutes adsorb weakly to silica gel and elute first; highly polar solutes adsorb strongly and elute last.
The non-polar mobile phase preferentially dissolves and transports less polar molecules down the column more quickly.
4
Arrange the compounds in sequence from least polar (first eluted) to most polar (last eluted).
Naphthalene →\rightarrow Chlorobenzene →\rightarrow Acetophenone →\rightarrow Benzoic acid.
This represents the exact elution sequence in normal-phase column chromatography.

Anahtar Kavram

Adsorption Column Chromatography Elution Order based on Solute Polarity
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Konular

Paper and Column Chromatography

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