Identification of Metal Cations and Paper Chromatography Introduction Understanding the reactivity of pollutant metals helps scientific understanding of that metal s impact on different environments These metals must be observed based off how they react with the addition of various solutes Paper chromatography consists of both a mobile and stationary phase which each are used to separate molecules or ions based on their intermolecular forces The paper acts as the stationary phase in this experiment Materials and Methods The materials used for the paper chromatography were 2 pieces of chromatography paper 2 600 mL beakers beaker for collecting waste 2 large watch glasses 1 spot plate tongs capillary tubes a ruler a pencil ammonia fumigation chamber and aluminum foil The chemicals used were 6 M HCl 1 5 M HCl 15 M NH4 OH 3 M NH4OH 3 M HCl DMG and transition metal solutions First four observations were performed on each of the five transition metal solutions Changes that occurred after the addition of HCl NH3 H2O and dimethylglyoxime to aqueous solutions of each metal were observed The five transition metals were Fe3 Co2 Ni2 Cu2 and Zn2 One drop of each of the five transition metal cation solutions were placed in separate spots on the spot plate The color of each cation solution was observed prior to adding an additional solute Then 2 3 drops of 3M HCl was added to each drop on the spot plate and each solution was observed for color change or lack thereof Afterwards the spot plate was cleaned off with distilled water into a waste beaker The process was repeated three more times with H2O 3 M NH4OH and DMG First allot for a 0 5 cm space at the top of the chromatography paper and write solutions 1 5 and unknown in even proportions Then allot for 1 cm of space at the bottom of the paper and separate each solution by drawing an x to mark the spot of each Use a capillary tube to place a dot of each solution and the unknown solution on the x Then observe the color of each solution Fold the paper into a cylinder and place it above the level of the solvent mixture into the 600 mL beaker filled with just enough 6 M HCl solution to cover the bottom of the beaker After cover the beaker with aluminum foil and remove the paper once the solvent has reached the top line Place the paper into the ammonia fumigation chamber for ten minutes and mark any visible spots with the pencil and observe any color changes Then spray the paper with DMG and place it back into the ammonia chamber for two minutes Lastly allow the paper to dry and measure the position of the solvent front and each spot to calculate Rf Repeat the above steps using 1 5 M HCl instead of 6 M HCl and record all observations Dispose of solutes and the chromatography paper in both the solid and liquid waste receptacles Results and Discussion For the transition metal test each metal cation underwent a color change except for zinc after the HCl NH3 and DMG were added to the spot plate However when H2O was added none of the cations underwent any color change apart from becoming more diluted Solution 1 was identified as Ni2 solution 2 was identified as Fe3 solution 3 was identified as Co2 solution 4 was identified as Zn2 and solution 5 was identified as Cu2 Solution 1 was initially light green 2 was yellow 3 was light red 4 was clear and 5 was light blue Refer to Table 1 to see the color changes each underwent with the addition of the various aqueous solutions Fe3 H2O HCl Orange yellow Yellow 2 Co2 pinkish Light pink NH3 Orange brown 3 Aqua blue 2 DMG Orange brown 3 Light yellow Ni2 green Light green 1 Translucent blue 1 Pink 1 Cu2 blue Light blue Zn2 colorless No reaction 5 Blue violet 4 Colorless 4 5 Dark green No reaction Table 1 While the spot plate tests cam determine the identity of unknown metal cations by themselves the tests would be useless against a mixture of metals The mixture would contain multiple cations which would combine colors proving it impossible to distinguish between the individual cations Zinc was consistently colorless in the spot plate tests The colors shown by ions were visible because of d to d transitions D to d transitions refer to an excited electron in a d orbital jumping to a higher orbital In zinc the d to d transition completely filled it s highest orbital causing color producing reactions to halt This lack of reaction caused the zinc to appear colorless When the Rf values of the two unknown components 32 and 32 were compared to the Rf values of the standard solutions the unknown components were determined to be The Rf values of this experiment are shown in Figure 2 Cation Rf Less Acidic Solvent Rf More Acidic Solvent Fe3 Ni2 Co2 Cu2 Zn2 Unk Comp 1 Unk Comp 2 0 40 cm 24 cm 024 cm 14 cm 72 cm 32 cm 32 cm 97 cm 80 cm 50 cm 55 cm not calculated 55 cm 51 cm Table 2 The Rf values also showed the mobility of metals when exposed to different acidic solutes The more acidic the environment was the more mobile the metal was and the higher the Rf value was The metals moved further up the chromatography paper in the more acidic environments If two different metal ions produce the same Rf values then they can still be distinguished with the results of paper chromatography The color of the unknown ions would have to be compared to the standard solutions as well as the Rf values One source of error is that when the paper cylinder was placed in the beaker the bottom was not curved properly and so a corner was touching the edge of the beaker This caused the solute to travel faster up the paper in a certain place which may have skewed the results by causing one solution to reach the topline when in actuality it may have been another solution Another source of error was that the capillary tubes did not provide an exact amount of solution on the paper Conclusion The metal cations apart from Zn2 each experienced a color change with the addition of HCl NH3 and DMG For the paper chromatography solution 2 reached the topline first and as a result the solution travelled the furthest using the 1 5 M HCl Each solution was measured for both the distance traveled by the compound and the distance traveled by the solvent to calculate Rf