What is chalk chromatography?

Answer 1

In 1906, Mikhail Tswett, a Russian botanist, published a paper in which he described the separation of pigments,

extracted from green leaves, by washing the mixture with petroleum ether (similar to lighter fluid) through a glass

tube packed with powdered calcium carbonate (chalk). As the mixture of pigments passed down the CaCO3

-filled

tube, they separated into distinctly colored zones. Tswett gave the name chromatography (the graphing of colors) to

this separation technique.

The method that Tswett used is known today as column chromatography. Column chromatography is a rather slow

and sometimes difficult process to carry out compared with more recent developments known as paper

chromatography, thin layer chromatography, gas chromatography, high pressure liquid chromatography, and ion

chromatography.

The method of column chromatography can be carried out in the classroom using calcium carbonate in the form of

sticks of chalk. A mixture containing two or more components is deposited on a stick of chalk, a solid adsorbing

substance. The components are adsorbed (i.e., held on the surface of the solid substance) to varying degrees which

depend on the nature of the component, the nature of the adsorbant, and the temperature. Then the wash solvent

(liquid) is added to the adsorbant and allowed to flow through it by capillary effect. As the solvent passes the

deposited mixture, the components tend to be dissolved to varying extents and are swept along the solid adsorbant.

The rate at which a component will move along the solid depends on its relative tendency to be dissolved in the

solvent and its tendency to be adsorbed on the solid. The net effect is that, as the solvent passes slowly through the

solid adsorbant, the components of the mixture -separate from each other and move along with the solvent forming

rather diffuse zones or spots. With the proper choice of solvent and adsorbant, it is possible to resolve many complex

mixtures into their components.

Answer 2

Chalk chromatography is a technique that involves using chalk as a stationary phase for chromatographic separation. The components in a mixture are separated as they move through the chalk, based on differences in their affinities for the stationary phase. This technique is commonly used in mineral analysis and environmental studies.