Heats of Solution, Transition, and Formation of Three Crystalline Forms of Metaboric Acid.

Abstract

The three crystalline forms of metaboric acid HBO2 were prepared, purified, and analyzed. Heats of solution in water or of reaction with sodium hydroxide solution were compared with those of orthoboric acid H3BO3(c). The best values for the heats of transition at 25 °C are: (c,I) to (c,II), 2.33±0.23 kcal/mole; (c,II) to (c,III), 1.30±0.05 kcal/mole; (c,I) to (c,III), 3.63±0.24 kcal/mole. The following heats of formation at 25 °C were derived: −192.77 ± 0.35 kcal/mole for the cubic HBO2(c,I), −190.43 ±0.34 kcal/mole for the monoclinic HBO2 (c,II), and −189.13 ± 0.34 kcal/mole for the orthorhombic HBO2(c,III).