Experimental Determination of the Thermodynamic Properties of the Solubility Product Reaction of Calcium Hydroxide in Aqueous Solution
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Abstract
An experiment is proposed for undergraduate chemistry students, based on the solubility product reaction of calcium hydroxide, Ca(OH)₂, in aqueous solution:
Ca(OH)2 (s) ⇌ Ca2+ (ac) + 2 OH‒ (ac)
The apparent equilibrium constant (Ksp) was experimentally determined as a function of temperature at constant ionic strength. Since the solution is non-ideal due to the high solute concentration, the extended Debye-Hückel model was used to obtain the ion activity coefficients and calculate the thermodynamic equilibrium constant for each temperature. Subsequently, the van’t Hoff equation was fitted to the dataset to determine Δhr0 and Δsr0, as well as Δgr0 at 298.15 K, evaluating the associated uncertainties and comparing the experimental results with values reported in the literature. This experiment enables students to understand fundamental concepts of chemical equilibrium, thermodynamics, and electrolyte behavior, integrating theory and practice in a didactic protocol that reinforces analytical and experimental skills in physical chemistry.
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