Determining the Enthalpy of Vaporization of Salt Solutions Using the Cooling Effect of a Bubble Column Evaporator
-
Chao Fan [1] ; Richard M. Pashley [1]
-
[1] University of New South Wales, Australia
-
- Localización: Journal of chemical education, ISSN 0021-9584, Vol. 93, Nº 9, 2016, págs. 1642-1646
- Idioma: inglés
- Texto completo no disponible (Saber más ...)
-
Resumen
The enthalpy of vaporization (ΔHvap) of salt solutions is not easily measured, as a certain quantity of pure water has to be evaporated from a solution, at constant composition, and at a fixed temperature and pressure; then the corresponding heat input has to be measured. However, a simple bubble column evaporator (BCE) was used as a novel method that allowed undergraduate students to determine the ΔHvap value of a salt solution within an hour or so, because it only required temperature measurement (at a steady state) of the column solution and the inlet gas flowing into the column. In this article, by way of illustration, the ΔHvap value of a 0.5 M NaCl solution was determined using the BCE process. In this experiment the evaporative cooling effects of the column were also easily demonstrated, as the inlet air at room temperature cooled the column solution to less than 10 °C. The change that students measured directly demonstrated the endothermic process of water vaporization. The role of several basic physical chemistry concepts, such as vapor pressure, phase transition, and enthalpy, involved in this experiment can be reinforced. An unexpected property of some common salt solutions, of bubble coalescence inhibition, was also observed in this experiment.
