Question

In paper chromotography, what form are the metals ( Zn2+, Co2+, Cu2+, Cd2+ , Fe3+, and Ni2+) ions likely to exist in the moving phase (water/hydrochloric acid/acetone) and what groups in the structure of the stationary phase (cellulose) are interacting with the moving ions in solution?

Note: Filter paper (Whatman #1) serves as the stationary phase, and the mobile phase consists of a mixture of acetone and 6 M hydrochloric acid. A single spot of the mixture to be analyzed is applied near one edge of a sheet of filter paper. A spot of solution containing each of the cations that might be in the unknown mixture is also placed near the edge of the same sheet for comparison. The treated strip is then placed in a covered jar or beaker (which acts as a developing chamber) containing a shallow layer of the solvent mixture (see Figure 3). Since filter paper is very permeable to the solvent, the solvent begins to rise up the strip by capillary action. The various spots on the developed chromatogram will be highlighted by treatment with several chemical reagents to enhance their color. The reagents to be used are ammonia, dimethylglyoxime (DMG), and 8–hydroxyquinoline (oxine).

Answer 1

In paper chromatography, the solvent(moving phase) used is either a nonpolar solvent with aqueous HCl or a polar solvent with aqueous HCl. The metal ions like Zn2+, Co2+, Cu2+, Cd2+ , Fe3+, and Ni2+ etc. react with HCl to form their respective chlorides. These chlorides have different solubilities in the solvnt (moving phase).

Due to their different solubilities in the solvent front, they travel different distance over the stationary phase. The least soluble chloride travells the least distance having the least Rf value and the most soluble chloride travels the highest distance along with the solvent front having the highest Rf value.

The polar -OH group present in stationary phase (cellulose) interact with the ions and the polar solvent and helps intheir adsorption through capillary tubes.

All other component except -OH groups present in stationary phase (cellulose) interact with the ions and the nonpolar solvent and helps intheir adsorption through capillary tubes.