In paper chromotography, what form are the metals ( Zn2+, Co2+, Cu2+, Cd2+ , Fe3
ID: 896866 • Letter: I
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).
Explanation / Answer
The metals will be present in the form of hydrates. For example Fe^{3+} will be present in the form of [Fe(H_2O)_6]^{3+} and Ni^{2+} will be present in the form of [Ni(H_2O)_6]^{2+}
The stationary phase contains cellulose which contains -OH groups. These -OH groups form hydrogen bonds with hydrates of metal ions which are the moving ions in the solution.
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