The heat of solution of calcium iodide and the nature of dilute solutions of calcium in liquid ammonia at -33°

Thesis (M.A.)--Boston UniversityAn extension of the thermochemical study of the nature of dilute solutions of calcium in liquid ammonia initiated in this laboratory was made in this study. Calorimetric measurement of the heat of solution of calcium iodide, which had been prepared a deammoniation of the calcium iodide ammoniate, yielded a value of +63.5 kcal./mole at infinite dilution. A single measurement of the heat of precipitation of CaBr2•8NH3 when combined with other thermochemical data gave a heat of solution of calcium bromide of +64.1 kcal./mole. This is evidently in error since in numerous cases it has been shown that in liquid ammonia and water the heat of solution of the iodide is greater than the heat of solution of the bromide for a common metal. Using the heats of solution measured here and others from the literature heats of solvation were calculated for calcium metal, calcium bromide, calcium iodide, alkali metals (Li, Na, and K), alkali bromides, and alkali iodides. By combining these heats of solvation the heat effects for the following reactions involving calcium were evaluated; (A) 2I-(g)-2e-(g)-->2I-(am)-2e-(am)ΔH -63.6 kcal. (B) 2Br-(g)-2e-(g)-->2Br-(am)-2e-(am)ΔH -80.7 kcal. (C) 2Br-(g)-2I-(g)-->2Br-(am)-2I-(am)ΔH -17.1 kcal. Comparison of the above heat effect with those for the the same reactions derived from the widely studied alkali metals and their halides showed good agreement for the comparison involving A, and poor agreement for the comparison with B or C. Further study of these comparisons indicated errors in heats of solution of calcium bromide and some of the alkali halides (LiI, LiBr, and KBr) which when taken into account improved the comparison with B. Since the above comparisons were made on the assumption that calcium in liquid ammonia (in the metal and halide solutions) was doubly charged the agreement found above was interpreted as evidence for the existence of calcium as Ca++ in dilute solutions of liquid ammonia