The standard freshman General Chemistry laboratory uses freezing-point depression concept to determine the molar mass of a solute using the general equation ?TF = (KF) x (m) x (i) where ?TF = freezing point depression (oC); KF= the solvent cryoscopic constant (oC/ molal) m = molality of solution (mol solute/kg solvent) andi = van 't Hoff factor, characteristic of the solute degree of ionization We have developed a microscale procedure that uses a LabPro interface and aqueous solutions that are as low as 0.1g of solute in 3 mL water to determine the ionization constant of five carboxylic acids (Ka= 10-1-10-2 ) using the van 't Hoff factor at different concentrations. The data are the first ones reported at the freezing point of water. Moreover our procedure uses much smaller quantities than the standard titration procedures which lead to potentially significant accumulations of waste chemicals.

Use of a microscale freezing point technique to determine the ionization constant of carboxylic acids.

244th National Meeting (2012)

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