A Visual Demonstration of Preferential Absorption The preferential absorption of one solute from a mixture of solutes can be demonstrated by a simple and inexpensive technique in which the separation is visually evident. Materials and equipment needed are 0.01 M KMnO, aqueous solution, 0.005 M iodine, carbon tetrachloride, methyl red and methyl orange indicators, concentrated HCI, test tubes, and/or a blender. The experiment is more impressive when a blender is used because of the high degree of dispersion attained. If test tubes are used, place approximately 2 ml of CC4 in each of six test tubes. Add 2 ml each of the KMnO, solution and acidified methyl red to test tube 1 and ahake well. Upon separation of the two phases, the aqueous phase is seen to be deep purple while the organic phase is colored yellow. To prove that only oneof the solutes distributed itself between the two phsses, it is necessary to place 2 ml of KMn04 solution in test tube 2 and add 2 ml of acidified methyl red indicator to test tnbe 3. Shake both tubes and allow the phases to separate. Upon separation the organic phase in test. tube 2 is colorless while that of test tube 3 is yellow. Thus visual evidence is provided that the methyl red is distributed between the two phases snd not the KMnO*. A similar demonstration can be conducted using methyl orange indicator solution, 0.005 M iodine, and carbon tetrachloride. In test tube 4 place 2 ml each of the methyl orange and iodine solutions and shake well. Upon separation of the phsses the organic phase is violet while the aqueous phase is yellow. To test tube 5 add 2 ml of the iodine solution and to test tnbe 6, 2 ml of the methyl orange. Shake well and then allow the phases to separate. Upon separationit is observed that the organic phase is a deep violet in test tnbe 5 while in test tube 6 it is essentially colorless, indicating the iodine to be preferentially absorbed to the methyl orange. When a. blender is used approximately 300 ml of CC4 and equal quantities of the aqueous phase should he used. The blender should N n for five seconds or less per agitation phase. H A ~ G.Y FOLSTER DEPARTMENT OF CHEMICAL ENGINEERING STATEUNIVERSITY NEWMEXICO LASCRUCES.88001
322
/
Journal of Chemical Education
