| Aim | (a) To prepare one lyophilic and one lyophobic sol. (b) To dialyze the sols prepared in (a) above. (c) To study the role of emulsifying agents in stabilizing the emulsion of different oils. |
| Apparatus Required | (a) Starch, egg albumin, and gum for lyophilic sol Aluminum hydroxide, ferric hydroxide, and arsenous sulphide for lyophobic sol Distilled water Glass beakers Stirrer Hot plate (b) Dialysis bag Distilled water Lyophilic and lyophobic sols prepared in part (a) Glass beakers (c) Different oils (e.g., olive oil, coconut oil, etc.) Emulsifying agents (e.g., soap, egg yolk, etc.) Distilled water Glass beakers Stirrer |
| Theory | Surface chemistry is the study of the chemical and physical properties of surfaces and interfaces. A sol is a colloidal solution in which the dispersed phase is solid and the dispersion medium is a liquid. A lyophilic sol is a sol in which the dispersed phase is attracted to the dispersion medium, while a lyophobic sol is a sol in which the dispersed phase is not attracted to the dispersion medium. Dialysis is the process of separating solutes of different molecular sizes using a semipermeable membrane. Emulsions are colloidal dispersions of two immiscible liquids, where one liquid is dispersed in the other in the form of small droplets. Emulsifying agents are substances that help to stabilize emulsions by reducing the interfacial tension between the two immiscible liquids. |
| Procedure | (a) To prepare the lyophilic sol, mix a small amount of starch, egg albumin, or gum in a beaker containing distilled water and stir continuously to obtain a homogeneous mixture. To prepare the lyophobic sol, mix a small amount of aluminium hydroxide, ferric hydroxide, or arsenous sulphide in a beaker containing distilled water and stir continuously to obtain a homogeneous mixture. Observe the sols obtained and record the observations. (b) Take a dialysis bag and soak it in distilled water for about 30 minutes. Fill the dialysis bag with the lyophilic or lyophobic sol prepared in part (a) above. Seal the dialysis bag and place it in a beaker containing distilled water. Allow the dialysis to proceed for about 24 hours. Observe the changes in the beaker containing distilled water and in the dialysis bag, and record the observations. (c) Take equal amounts of different oils in separate beakers. Add a small amount of an emulsifying agent (e.g., soap, egg yolk, etc.) to each beaker and stir continuously to obtain a homogeneous mixture. Observe the emulsions obtained and record the observations. |
| Observation and Result | Observation: (a) Lyophilic sols are stable and homogeneous, while lyophobic sols are unstable and heterogeneous. (b) The solutes of smaller molecular size diffuse through the membrane and into the distilled water, while the solutes of larger molecular size remain inside the dialysis bag. (c) The emulsifying agent reduces the interfacial tension between the two immiscible liquids and stabilizes the emulsion. Result: One lyophilic and one lyophobic sol have been successfully prepared. The dialysis process has been studied, |