Diammonium hydrogenphosphate with Diammonium sulfate and Water (IUPAC SDS Volume 66)
Evaluator
Jitka Eysseltová Department of Inorganic Chemistry, Charles University
Evaluation
9.5. (NH4)2HPO4 - (NH4)2SO4 - H2O

Only a very limited amount of data is available for this system. There is a report of the 298 K isotherm.1 Another report2 presents the values for the isotherms at 273 K, 283 K and 293 K. And Akiyama, et al.3 have developed the following smoothing equation for this system:

S = A /(M + 1.2) [1]

where S is the solubility of (NH4)2HPO4 expressed as mass%; m is the mole ratio SO4/PO4 in the saturated solution; and A is a constant having the following values see in the table below.

t/°C A
0 43.6
25 43.9
50 56.4

A graphical comparison of some of the data at 293 K and 298 K as well as results calculated from Eq. [1] are shown on Fig. 27. From this comparison it appears, again, as if the work of Vol'fkovich, et al.1 is affected with a systematic error.

Figure
Solubility graph
FIG. 27. Solubility of (NH4)2HPO4 in the (NH4)2HPO4–(NH4)2SO4–H2O system.
Sources:

1 Vol'fkovich, S. I.; Berlin, L. E.; Mantsev, B. M.; Tr. NIUIFa 1940, 228.
2 Chernova, K. S.; Korzh, E. V.; Zh. Obshch. Khim. 16, 171 (1946).
3 Akiyama, T.; Kanzaki, H.; Minagawa, S.; Nippon Dojo Hiryogaku Zasshi 49, 243 (1978).