Column Chromatography (ch.8)

What is column chromatography?

A separation technique where a mixture passes down a column packed with silica or alumina, and components elute at different times based on polarity and interactions.

What is the stationary phase in column chromatography?

Silica gel (SiO₂) or alumina (Al₂O₃)—both are polar solids.

What is the mobile phase?

A solvent or solvent mixture that carries the sample down the column.

What is the main basis of separation in column chromatography?

Differences in polarity and adsorption strength between compounds.

How do polar compounds behave on silica or alumina?

They adsorb strongly → elute slowly.

How do nonpolar compounds behave?

Adsorb weakly → elute quickly.

How does solvent polarity affect separation?

Polar solvents push compounds faster

Nonpolar solvents move compounds slowly

What is flash chromatography?

Column chromatography performed under air pressure, speeding up solvent flow.

What is HPLC?

High-Pressure Liquid Chromatography—uses high-quality stationary phases and high pressure for fast, efficient separations.

What is the elutropic series?

A ranking of solvents by polarity or eluting power.

What does a higher dielectric constant ε* indicate?

More polar solvent → stronger eluting power.

Why must the column never run dry?

Air pockets disturb the adsorbent → poor separation and streaking.

How full should the column be with adsorbent?

Typically ½ to ⅔ full.

What are the two methods of packing a chromatography column?

1. Dry packing

2. Slurry packing

What is dry packing?

Silica/alumina powder added dry, gently tapped to settle evenly, then wetted with solvent.

What is slurry packing?

Adsorbent mixed with a solvent to form a slurry, then poured into the column.

Why is slurry packing often better?

Reduces air bubbles and gives more uniform packing → better separations.

Which compound elutes first: polar or nonpolar?

Nonpolar (weak adsorption).