IUPAC-NIST Solubilities Database

IUPAC-NIST Solubility Database
NIST Standard Reference Database 106

Solubility System: Diammonium hydrogenphosphate with Water

Components:
   (1) Diammonium hydrogenphosphate; (NH4)2HPO4; [7783-28-0]  NIST Chemistry WebBook for detail
   (2) Water; H2O; [7732-18-5]  NIST Chemistry WebBook for detail

Original Measurements:
   Buchanan, G.H.; Winner, G.B., Ind. Eng. Chem. 1920, 12, 448.

Variables:

   Concentration = Composition and temperature.

Prepared By:
   J. Eysseltová

Experimental Data:   (Notes on the Nomenclature)
(Please see footnotes following the table(s).)

Table I. Analyses for NH₃ and P₂O₅ with special attention given to possible loss of ammonia due to hydrolysis of (NH₄)₂HPO₄.
t/°C	Chemical₁	Mass Fraction w₁^(a)	Chemical₂	Mass Fraction w₂^(a)	Comment(s)
0	NH3	7.69 up (a) 7.62 down (a) 7.66 mean	P2O5	16.28 up (a) 16.28 down (a) 16.28 mean	P/N ratio 0.470 % di-salt 96
10	NH3	9.89 up (a) 9.85 down (a) 9.87 mean	P2O5	20.70 up (a) 20.61 down (a) 20.66 mean	P/N ratio 0.478 % di-salt 99
20	NH3	10.54 up (a) 10.46 down (a) 10.50 mean	P2O5	21.94 up (a) 21.89 down (a) 21.92 mean	P/N ratio 0.480 % di-salt 100
30	NH3	10.87 up (a) 10.89 down (a) 10.88 mean	P2O5	23.00 up (a) 23.00 down (a) 23.00 mean	P/N ratio 0.473 % di-salt 97
40	NH3	11.45 up (a) 11.46 down (a) 11.46 mean	P2O5	24.47 up (a) 24.55 down (a) 24.51 mean	P/N ratio 0.467 % di-salt 95
50	NH3	12.06 up (a) 12.20 down (a) 12.13 mean	P2O5	25.41 up (a) 25.34 down (a) 25.38 mean	P/N ratio 0.478 % di-salt 99
60	NH3	12.58 up (a) 12.55 down (a) 12.57 mean	P2O5	26.80 up (a) 26.90 down (a) 26.85 mean	P/N ratio 0.468 % di-salt 95
70	NH3	13.07 up (a) 13.22 down (a) 13.15 mean	P2O5	27.58 up (a) 28.01 down (a) 27.80 mean	P/N ratio 0.473 % di-salt 97

Table II. Solubility in the (NH₄)₂HPO₄-H₂O system derived on the basis of the data in Table I.
t/°C	Composition₁ [g/100 g H2O]	Mass Fraction w₁^(a)	m₁ [mol/kg]^(e)	Mass Fraction w₂^(b)	Mass Fraction w₃^(c)	Mass Fraction w₄^(d)
0	---	29.7	3.25	30.3	30.0	---
10	62.8	38.3	4.72	38.4	38.4	38.6
20	69.0	40.7	5.22	40.8	40.8	40.8
30	75.2	42.2	5.60	42.8	42.5	42.9
40	81.8	44.4	6.20	45.6	45.0	45.0
50	89.2	47.0	6.74	47.2	47.1	47.2
60	97.3	48.8	7.39	49.9	49.4	49.3
70	106.0	51.0	8.01	51.8	51.4	51.4

Notes:
   Table 1  ^a  The way of equilibration.
   Table 2  ^a  Solubility as mass % calculated on the basis of the analysis for NH₃.
   Table 2  ^b  Solubility as mass % calculated on the basis of the analysis for P₂O₅.
   Table 2  ^c  The mean of w₁ and w.
   Table 2  ^d  The value of w₃ was calculated from the formula: w₃ = 36.5 + 0.213 t/°C.
   Table 2  ^e  The molalities were calculated by the compiler, using the value of w as the starting point.

Method/Apparatus/Procedure:
   The samples were placed in 2 glass bottles of about 250 cm³ capacity. In one of them, the equilibrium was approached from below, in the other from above. Samples of the satd soln were withdrawn by a special weighing pipet and analyzed. NH₃ was determined by the distillation method and P₂O₅ was determined by precipitation as "double magnesium salt" (NH₄MgPO₄--compiler). The temperature of the thermostatic bath was controlled by the introduction of steam or ice water. At higher temperatures an electric hot plate was used. For the highest temperatures, calcium chloride brine was used in the bath.

Source and Purity of Materials:
   The salt was prepared by ammoniating a nearly saturated solution of mono-salt at a temperature above 80 °C, cooling the mixture and filtering the crystals, and air drying them. Analyses     experimental     calculated NH₃               14.80       14.80     P₂O₅             61.57        61.72

Estimated Errors:
   Solubility: The compiler estimates the reproducibility of the solubility values to be approximately 1 %.
   Temperature: The temperature was kept constant to within 0.5 K.