Investigating the Relationship between Variance of Transition Temperatures

Abstract

Colligative properties are properties of impurities. Most substances are mixtures since it is difficult to maintain a completely pure substance. The effects of a solute on the properties of a substance include freezing point depression (FPD) and boiling point elevation (BPE). These properties are due to the impurity lowering the mole fraction of the solvent, consequently decreasing its chemical potential. This stabilizes the liquid state and causes the solvent to exist as a liquid for a wider range of temperatures at constant pressures. The purpose of this study is to investigate a general relationship between FPD and BPE. Specifically, the study aims to provide a method in determining a proportionality between the transition constants of a general solvent. The transition constants represent how much the variance of transition temperatures change against varying concentrations of solute. The transition constants (K_fp and K_bp) are determined for water with varying concentrations of dissolved acetic acid, sucrose, and sodium chloride. The freezing point and boiling point of the solutions determined with analysis of cooling and heating curves, and the variance of transition temperature is determined upon comparison with pure controls. Boiling point elevation has been found to be positively correlated with freezing point depression, increasing by a factor of 0.35 (± 0.09 s.d.). The experiments designed in this study provide a simple reproducible way of demonstrating and supporting the fundamental principles underlying colligative properties.