CHE 211 Study Guide - Midterm Guide: Column Chromatography, Silica Gel, Elution
Organic Chemistry 2 – Chemical Purification & Separation
Gravity Column Chromatography
The sample on the column is subjected to two opposing forces: the solvent dissolving it
and the adsorbent adsorbing it
This dissolving and adsorption is an equilibrium process as some of the compound
being adsorbed on the adsorbent (silica gel), the other molecules of the compound are
leaving the adsorbent and returning to the solvent and they are moved further down
the column and be re-adsorbed again
The NON-POLAR compounds come off the column more RAPIDLY than the polar
compounds
o A non-polar compound that is very soluble in the solvent but not strongly
absorbed by the polar stationary phase, will move through the column very
rapidly
o A polar compound on the other end that is attracted to the absorbent will move
through the column more slowly
▪ Because of the different rates of the components of the
mixture while moving down the column, the mixture is
separated into bands
▪ If the compound to be separated is coloured, the bands
will be visible and if the compound is colourless, the bands
will not be seen
▪ The bands are finally eluted out of the column, with each
band to be collected in a different flask/test tube
▪ This is the order of elution for
the following groups
▪ Notice that non-polar
functional groups elute first as
the more polar functional
groups remain on the column
longer
▪ We are going to concentrate on
3 parts of gravity
chromatography (keep in mind that whatever we say about gravity column
chromatography, it will also apply to flash chromatography)
1. The adsorbent
2. The solvent
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Document Summary
Organic chemistry 2 chemical purification & separation. The sample on the column is subjected to two opposing forces: the solvent dissolving it and the adsorbent adsorbing it. 3 parts of gravity chromatography (keep in mind that whatever we say about gravity column chromatography, it will also apply to flash chromatography: the adsorbent, the solvent, and collecting the fractions. The adsorbent is selectively adsorbs colored compounds, very similar to decolourizing charcoal (this is mentioned during recrystallization) Intermolecular bonding such as dipole-dipole attractions or hydrogen bonding are responsible for adsorption process. Common adsorbents include silica gel, sio2, and alumina, al2o3 both of these are polar adsorbents, however, alumina is more polar than silica gel. Adsor(cid:271)e(cid:374)ts (cid:272)o(cid:373)e i(cid:374) differe(cid:374)t (cid:862)mesh(cid:863) sizes, such as silica gel 60 or silica gel 230- The larger the mesh number, the smaller the adsorbent particles. The particle size of the adsorbent affects how the solvent flows through the column.
