Improvement of Accuracy and Precision during Simple Distillation of Ethanol-Water Mixtures

The simple distillation of ethanol-water mixture is a well-known experimental subject in either general chemistry laboratory or organic chemistry laboratory. The objective is to provide a reliable guidance for college students who are major in chemistry or chemical engineering to obtain repeatable results during the simple distillation of ethanol-water mixture. The liquid-vapor phase diagram of ethanol-water mixtures was introduced before experiment. As similar to a tradition distillation assembly, Liebig condenser, specific gravity hydrometer set, and heating mantle were mainly employed to perform the experiment of a simple distillation with minor but critical changes. The examination of diverse results in distillate amounts and distillate ethanol concentrations were analyzed by Rayleigh equation. The simple distillation was evaluated at the assigned temperature that was selected from liquid-vapor phase diagram. Even though the first evaporation started at a temperature below the theoretical bubble point shown in liquid-vapor phase diagram in most cases, the set temperature was gradually adjusted and maintained until no more vapor generated. In fact, this work motivates students to design their simple distillation plans through changing initial ethanol concentration and set temperature. The experimental data from 23 groups suggest that the accuracy and the precision were dependent upon how to control heating rates and to sustain set temperature in this work.