S. ALLULLI
1084
Solubilities of Ammonia in Alkali Nitrate and Perchlorate Melts' by S. Allulli Laboratorio d i Chimica delle Radiasioni e Chimica Nucleare del C.N.E.N., Istituto d i Chimica Generale ed Inorganica, Universita d i Roma, Rome, Italy
(Received May 2 , 1 9 6 8 )
The solubility of ammonia at pressures between 5 and 50 mm in various (Li-K) NO3 mixtures, in (Li-Na-K) NO3 eutectic, and in (Li-K) c104 eutectic at different temperatures has been determined. The solubility increases with increasing Li+ ion concentration and decreases with increasing temperature. Henry's law constants (moles of solute/mm mole of solvent) are about for (Li-K)NOa mixtures and (Li-K)C104 and eutectic, respectively. The influence of the composition of the solvent on the solubility of the ammonia and the mechanism of the dissolution process are discussed. To test the relationship between the absorption of polar gases and their dipole moments, solubility measurements of hydrogen sulfide, carbon monoxide, chloroform, and acetone in molten (Li-K)NOs eutectic at 160' were also attempted, but in all cases the solubilities were found to be too small (> HzS. The plot of the enthalpy of solution of ammonia us. Li+ mole fraction for the melts investigated (Figure 3) appears linear for (Li-K) NO8 mixtures; a similar behavior was observed by Bertozzi5” for the solubility of water in molten alkali nitrates. It is evident that the data obtained for the (Li-NaK)NO3 eutectic and (Li-K)C104 eutectic do not fall on the curve. This is not surprising if, as suggested by other authors,15,16several kinds of association of the solvent ions take place in these melts depending upon crystal radius, electric charge, and temperature. Since the “activity” of lithium ions depends upon the anions and the cations present in the melt, the more negative value found for the (Li-K)C104 eutectic is expected if one considers this system as more acidic than the corresponding (Li-K)N03 system. It is interesting to observe that the electrophoretic behavior of inorganic anions [Cl(I), Cr04(II), NOa(1) etc.] in molten .(Li-K) C104 eutectic agrees with this suggestion, since all the anions examined behave as cations or stay at the application point.le A similar explanation may hold for the (Li-Na-K) NOs eutectic since the substitution for potassium by smaller sodium ions raises the “activity” of lithium ions; nevertheless, in this case, sodium ions (owing to their small crystalline radius) can also contribute directly t o the ammonia solubility. Further investigations on the behavior of polar, molecular species added to these highly ionized melts seem t o be of interest in order to contribute to the knowledge of the properties of extremely concentrated electrolyte solutions. Acknowledgment. The author wishes to express his thanks to Professor G. Alberti for many helpful discussions.
0.2
0.4
0.6
0.8 ---I- Li’rnole
1.0
fraction
Figure 3. Enthalpy of solution of ammonia us. Li+ mole fraction: -6 (Li-K)NOa mixtures; (Li-Na-K)N03 eutectic; f’ 2, (Li-K)CIOd, eutectic.
2,
(13) E. A. Moelwyn-Hughes, “Physical Chemistry,” Pergamon Press, London 1957, p 597. (14) R. Furth, Proc. Cambridge Phil. Soc., 3 7 , 252 (1941). (15) F. Lantelme and M. Chemla, EZeclrochirn. Acta, 10, 665 (1965). (16) G. Alberti and 9. Allulli Chrornatogr. Rev., 10, 99 (1968).
Volume Y3,Number 4 April 1969
