Determination of Solubility Products of Rare Earth Fluorides by Fluoride Ion-selective Electrode

Solubility product values of the rare earth fluorides were determined potentiometrically by using fluoride ion-selective electrodes at 25.0 °C. The pKsp values of the lanthanoid fluorides decreased gradually from 20.0 to 16.9, while the value for yttrium fluoride was locate in between those of terbium and dysprosium fluorides. The value for scandium fluoride was appreciably smaller than any of the lanthanoid fluorides, as expected from the cationic radii. The solubility product value of lanthanum fluoride single crystal could not be determined, since the saturated solution was not obtained through measurements of over three months.