Question

In paper chromtography, what is the nature of the attractions between the stationary phase (cellulose) and the moving phase (hydrochloric acid/water/acetone) and the species ( Zn2+, Co2+, Cu2+, Cd2+ , Fe3+, and Ni2+ in two unknown solutions)  being separated, in particular what affects the Rf values and how?

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

1) In paper chromatography, the Calculation of Rf (retention factor) depends on distance travelled by metal ion, i.e

Rf = distance travelled by metal ion/ distance travelled by solvent

2) In this movement of metal ions depends on mobile phase (water + HCl + acetone) and Stationary phase (paper i.e cellulose).

3) Acetone with Hcl in mobile phase play key role in attracting metal ions.It means Hcl provides cl- ions which converts metal ions to metal chlorides which are highly polar and it is the form they are transported.

4) In addition to Paper or stationary phase is cellulose material which is polymer of many OH- ions which are also attracts the metal chlorides.

5) Mean while the attractions between solvent (mobile phase) and cellulose ( stationary phase ) in the form of dipole-dipole, ion-dipole, dipole-hydrogen bonding.

6) Finaly the ions are in between the -C=O of acetone and -OH groups of cellulose like sandwich model and immobilised. so, the metals of more +ve charge are atrongly binded and not moved but low charge metals move fastly and show higher Rf values