This experiment will separate the components of a mixture on the basis of their differing absorptive tendencies on a stationary phase, which is the method of chromatography. The mobile phase will consist of four distinct transition metal cations dissolved in an acetone-hydrochloric acid eluent, along with three unknown solutions; the identities of these will be determined based on a comparison of the Rf value of these to the known cations.
First to be prepared was the stationary phase, or chromatographic paper, which in this case was filter paper. Given only large sheets, it was cut into a rectangle with 20 cm length and 10 cm width. Before cutting, though gloves were put on so that skin oil would not stain the filter paper. Also, the filter paper was not laid on the lab table, but on a paper towel. With a pencil, a line was drawn 2 cm from the bottom edge of the paper. Marks were put on the line, 2 cm apart, and labeled with the appropriate cations and the unknowns labeled as U1, U2, and U3. The stationary phases were then spotted with the corresponding knowns and unknowns, then dried under a heat lamp. This spotting process was repeated 3 times. It was done using glass capillary tubes; these used adhesive and cohesive forces to draw up the cation solutions into the tube and subsequently released them onto the filter paper when touch. With the stationary prepared, the developing chamber was made. In a 600-ml beaker 9 ml of acetone and 1ml of 6 M HCl were combined (under a fume hood) to prepare a total of 10 ml of eluting solution. The solution was carefully poured into the beaker without touching the sides using a sting rod. The solution that was created was made sure to be under 1.5cm so that it does not touch the spots on the chromatography paper that had been prepared. Saran wrap was torn to cover the entire top of the beaker tightly. Thus, the developing chamber was created. Next, the stationary phase was prepared for elution. The filter/chromatography paper was formed into a cylinder, carefully so that the edges would not touch. Holding the edges apart, the paper was stapled into shape. The spots were checked again to make sure they were dry and made sure to be high enough above the bottom edge so that it does not touch the eluent. The paper cylinder was then placed in the developing chamber (Saran wrap removed), careful not to touch the sides of the beaker; if it did the eluent would not rise and separate the particles effectively. The plastic wrap was replaced to tightly seal the chamber. When the eluent front moved to within 2 cm from the top of the filter paper, the plastic wrap was removed and the beaker was brought back to the lab table; however, the beaker remained undisturbed until this point.
The paper was removed from the developing chamber and the eluent fronts (the very top of the fronts) were marked with a pencil line. The chromatogram was allowed to dry under the fume hood. Afterward, the colored bands on the paper were circled with a pencil, including both the known and unknown cations. An enhancement reagent was then used to intensify the appearance of the metal cation bands on the paper. This was done using an ammonia chamber that was already prepared by the instructor under the fume hood. It contained concentrated NH3, covered by a tub. After about 15 min the deep blue color of Cu2+ was evident, so the chromatogram was removed and any new transition metal ion bands that appeared were circled. The top of each band was marked.
Finally, to determine the Rf value for each of the solutions, the distance from the origin of the ion to the top of the color band was measured and this became the Dion value. Additionally, the distance from the origin of the ion to the eluent front was measured; this was the Dsolvent value. The composition of the unknowns was found by comparing the Rf value of each of the known cations with the unknowns (and the unknowns produced anywhere from one to three bands or one to three cations).