A simple apparatus for the measurement of colligative properties in aqueous electrolyte systems: an educational approach

The importance of systems with electrolytes is well known nowadays, and many examples can be given about their industrial applications. However, at undergraduate level the properties of electrolyte solutions are neither theoretically nor experimental]y focused in accordance to the role they play in chemical industry. In this work simple equipment for the measurement of freezing point depression due to the presence of strong electrolytes in water is introduced. A study with the salts NaCI and XCI in the molality range up to 4 molal is suggested. In this way, the students may gain some insight on the physical-chemistry of aqueous electrolyte solutions. The experimental data are compared with the values obtained from available models to calculate the activity coefficients of the salts and water activities, mainly those concerned with the Debye-Hückel equation and its empirical extensions. It is also suggested to use those equations and the data to model the freezing point depression at high electrolyte concentrations.

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