Europium fluoride

The fluoride content of a solution is measured with an electrode made from a mixture of lanthanum and europium fluorides. Lanthanum follows barium in the periodic table and has an atomic number of 57. Lanthanum is also the first of a series of 15 heavy metals before hafnium called lanthanides. Europium is a lanthanide and its atomic number is 63. The mode of action of the fluoride electrode is described in Chapter 16, sect. 16.1.1. 

Cu20 DICOPPER OXIDE 622 EuF3 EUROPIUM FLUORIDE 666... 

CuFe02 COPPER IRON DIOXIDE 623 EuF3[g] EUROPIUM FLUORIDE (GAS) 667... 

Lanthanum fluoride, Lal- u is a nearly ideal substance for the preparation of a crystalline membrane electrode for the determination of fluoride ion. Although this compound is a natural conductor, its conductivity can be enhanced by doping with europium fluoride, LuF,. Membranes are prepared by cutting disks from a single crystal of the doped compound. 

The fluoride ion selective electrode is the most commonly used single crystal ISE. It is shown schematically in Fig. 15.9. The membrane is a single crystal of LaF3 doped with EuF2. The term doped means that a small amount of another substance (in this case, EUF2) has been added intentionally into the LaF3 crystal. (If the addition were not intentional, we would call the europium an impurity or contaminant ) Note that the two salts do not have the same stoichiometry. Addition of the europium fluoride creates fluoride ion vacancies in the lanthanum fluoride lattice. When exposed to a variable concentration of F ion outside the membrane, the fluoride ions in the crystal can migrate. Unlike the pH electrode, it is the F ions that actually move across the membrane and result in the electrode response. The F ISE is extremely selective for fluoride ion. The only ion... 

We believe that the calculation of the enthalpies of atomization of samarium and europium fluorides from the data reported by Kleinschmidt et al. (1981) is more correct and that the reactions involving SmF and EuF studied by Zmbov and Margrave (1967a) should be considered when discussing AatH°(HoF, 0). In addition, we tried to calculate both AatH°(RF, 0) and AatH°(RF2, 0) from the enthalpies of reactions with low stoichiometric coefficients. 

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