| Demonstration Experiment on Video Objectives: Solubility, Polarity, Salting-Out Effect Peter Keusch |
|
German version
Hazards and safety precautions:
Safety glasses and protective gloves must be worn. Effective ventilation required.
| A gas washing bottle is filled with 60 mL of methanol / H2O (1:1). Using a powder funnel 40 g of K2CO3 are added to the aqueous solution. Residual salt paricles clinging to the wall of the gas washing bottle are removed by shaking the bottle. The mixture is stirred, until the two phases have seperated. The aqueous phase turns blue upon addition of a spatula tip full of CuSO4 · 5 H2O. After a few crystals of K2Cr2O7 are added the color turns green (mixed color). The alcoholic layer turns yellow when it is mixed with a spatula tip full of methyl red. The yellow-green two-phases system is overlayered with 60 mL of a solution of Sudan III (a spatula tip full) in 60 mL of toluene. Results: When the stoppered bottle is shaken the three layers temporarily mix, yielding a different color (i.e. blue, yellow and blue combine to make brownish). When stop moving the bottle the three liquids separate again. The colors of three dissolved compounds are visible again.   Video clip (Download RealPlayer .rm file)
Discussion: · Substances that have similar polarities will be soluble in each other ("likes dissolve likes"). Water and methanol are miscible in all proportions but the two liquids are made immiscible by the addition of potassium carbonate. The weak intermolecular forces ( i.e. hydrogen bonds) between methanol molecules and water are disrupted by the hydration of the ions. The process of salting out allows the separation of an organic phase from an aqueous phase. · Toluene is non-polar. The methanol and water molecules, respectively, attract only one another, while ignoring the non-polar liquid. · The result is that the three liquids are immiscible Index of Lecture Experiments 
|
