Freezing depression measurements are generally used to determine the molecular weight of an unknown solute. This project involves the use of microscale probes to determine the ionization constant of four carboxylic acids using the experimentally obtained value of the van't Hoff factor of their aqueous solutions. The quantities used are as low as 0.1g of the carboxylic acid and 4mL of water. The carboxylic acids used in this study are dichloroacetic, trichloroacetic, maleic and malonic acids.