6th ISF

MATS005 - CORRELATIONS BETWEEN SOLUBILITY OF IMPURITIES ON MELTING POINT OF MIXTURES: A CASE STUDY OF OPTIMIZING THE USE OF SALT ON MELTING ICE

Adding impurities for depressing melting points is commonly used nowadays, antifreeze proteins are added into lakes to inhibit the formation of ice crystals and ethylene glycol is introduced into water as car coolants. In high-latitude regions, heavy snow is serious and disrupts traffic. Adding salt is one of the resolving methods. The phenomenon of melting point depression can be widely seen in nature and human society. Moreover, there is not a large amount of research on mathematical models of the phenomenon other than Eutectic Calculation which is based on Gibbs free energy, and the data required may not be readily available. Therefore, this study aims to correlate the solubility of impurities in different mixtures to the melting point of the mixture which is simpler as the solubility of substances could be easily found by experiments. The optimization of salt for melting ice was used as a starter to investigate the effect. Cations and anions are formed on the surface of snow when salt is added. Water molecules gain potential energy when salt becomes hydrated and releases heat. Therefore, snow can melt at a lower temperature. It was hypothesized that salts with higher solubility in water melt snow more efficiently. This is related to the stoichiometry of the above exothermic process. In this study, different amounts of 4 types of common salts (e.g. NaCl and CaCl₂), were dissolved in water. They were cooled to -13 °C and warmed under constant ambient temperature. Temperature-time graphs were plotted. The second derivative is calculated for each Temperature-time plot and the points of inflection were defined as their melting points. Like using salt with higher solubility in water, solutions with higher concentrations of impurities showed the same effect. Results from this study echoed the results from research on melting point depression in agricultural soils using permittivity and temperature measurements (R. Pardo Lara, 2020). The correlation between melting point and solubility shall be a powerful tool for the industrial sector in producing products that are sensitive to a melting point like fuses as the time of doing trial-and-error can be shortened.

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