Separating and Identifying Ions in Solution
September 29, 2008
The purpose of this experiment is to determine the metallic ions that exist in an unknown solution using paper chromatography. First we will determine the quantitative Rf values, well as perform qualitative analysis of the chromatography paper, of three known substances. Second, we will use a staining reagent to distinguish between the different ions present. Third, we will compare the Rf values of the known metallic ions, and observe the actual color and placement of those ions on the chromatography paper, and compare the data with the results of the unknown solution. From that data we will be able to state the composition of the unknown solution.
The fact that different substances have different solubility’s in a given solvent can be used in several ways to effect a separation of substances from mixtures in which they are present. In this chromatographic experiment a mixture is deposited on a sheet of chromatography paper. The components of the mixture are absorbed on the chromatography paper (hereinafter referred to as paper) to varying degrees, depending on the nature of the component, and the temperature. A solvent is then caused to flow through the paper by capillary effect. As the solvent passes the deposited sample, the various components tend, to varying extents, to be dissolved and swept along the paper. The rate at which a component will move along the paper depends on its relative tendency to be dissolved in the solvent and absorbed on the paper. The net effect is that, as the solvent passes slowly through the solid, the components separate from each other and move along as rather diffuse zones. With the proper choice of solvent and absorbent, it is possible to resolve many complex mixtures by this procedure. If necessary, we can usually recover a given component by identifying the position of the zone containing the...