Tactile Column Chromatography (Years 10-13)

Background

Chromatography is a technique used to separate or purify mixtures.

Column chromatography involves a liquid mobile phase and a solid stationary phase.

Components normally interact with the mobile phase and stationary phase via intermolecular interactions.

Task: See if you can name the intermolecular interactions and put them in order of strength.

The rate at which each component moves down the column is determined by its relative affinity for the mobile phase and stationary phase.

Image showing how column chromatography works: The column is filled with a stationary phase, the sample is added to the top of the stationary phase, the mobile phase is added to the column and the components in the sample gradually separate.
Diagram showing how column chromatography works

In normal phase column chromatography, the stationary phase is polar and the mobile phase is non-polar. therefore _______ components interact more strongly with the stationary phase and move through the column ______.

In reverse phase column chromatography, the stationary phase is non-polar and the mobile phase is polar. . therefore _______ components interact more strongly with the stationary phase and move through the column ______.

Image showing the difference between normal phase column chromatography and reverse phase column chromatography.
Diagram showing the difference between normal and reverse phase column chromatography

          _______ phase chromatography         _______ phase chromatography

Silica

Silica (SiO2) is a common stationary phase. You can find silica in sand on the beach. But the silica in columns is a bit different. It has lots of holes in it, called pores. The surface of all those holes is covered in Si-OH groups. We call these silanol groups. The holes give the silica a really high surface area. This means lots of space for polar molecules to stick to!

Image showing the structure of silica: Pores with -OH functional groups on the surface.
Image showing the structure of silica

The tactile model

The tactile model can be used to illustrate the way in which column chromatography works. The plastic and wool felt balls represent the components in the mixture and the Velcro inside the column represents the stationary phase.

Task: Pour the balls down the column and feel which balls come out.

Image showing the tactile column apparatus: Plastic balls, wool balls and a column with a velcro interior
The tactile column apparatus

Question 1: Why did the balls separate in the column

Question 2: Relate this back to standard chromatography

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