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IUPAC-NIST Solubility Database
NIST Standard Reference Database 106
Solubility System:
Diammonium hydrogenphosphate with Disodium hydrogenphosphate and Water
Components:
(1) Diammonium hydrogenphosphate; (NH4)2HPO4; [7783-28-0]
NIST Chemistry WebBook
for detail
(2) Disodium hydrogenphosphate; Na2HPO4; [7558-79-4]
NIST Chemistry WebBook
for detail
(3) Water; H2O; [7732-18-5]
NIST Chemistry WebBook
for detail
Original Measurements:
Platford, R.F., Chem. Eng. Data 1974, 19, 169.
Variables:
Concentration = Composition at 25 ºC.
Prepared By:
J. Eysseltová
Experimental Data:
(Notes on the Nomenclature)
(Please see footnotes following the table(s).)
Solubility in the Na
2
HPO
4
-(NH
4
)
2
HPO
2
-H
2
O system at 25 °
Chemical
1
10
2
* Mass Fraction w
1
m
1
[mol/kg]
(a)
Chemical
2
10
2
* Mass Fraction w
2
m
2
[mol/kg]
(a)
Solid Phase(s)
(b)
Na2HPO4
10.4
0.82
(NH4)2HPO4
0.00
0.00
A
Na2HPO4
12.3
1.01
(NH4)2HPO4
2.0
0.18
A
Na2HPO4
16.0
1.39
(NH4)2HPO4
3.3
0.31
A + B
Na2HPO4
15.6
1.38
(NH4)2HPO4
4.6
0.44
B
Na2HPO4
13.6
1.19
(NH4)2HPO4
5.9
0.55
B
Na2HPO4
11.3
0.97
(NH4)2HPO4
7.0
0.65
B
Na2HPO4
10.5
0.92
(NH4)2HPO4
8.9
0.84
B
Na2HPO4
9.7
0.88
(NH4)2HPO4
12.8
1.25
B
Na2HPO4
9.1
0.84
(NH4)2HPO4
14.4
1.42
B
Na2HPO4
8.2
0.78
(NH4)2HPO4
18.0
1.85
B
Na2HPO4
8.4
0.83
(NH4)2HPO4
20.4
2.17
B
Na2HPO4
8.0
0.85
(NH4)2HPO4
25.5
2.90
B
Na2HPO4
7.8
0.90
(NH4)2HPO4
31.2
3.87
B
Na2HPO4
8.5
1.16
(NH4)2HPO4
40.1
5.91
B + C
Na2HPO4
7.1
0.97
(NH4)2HPO4
41.3
6.06
C
Na2HPO4
4.8
0.62
(NH4)2HPO4
40.8
5.68
C
Na2HPO4
1.8
0.22
(NH4)2HPO4
41.3
5.50
C
Na2HPO4
0.0
0.00
(NH4)2HPO4
41.5
5.37
C
Notes:
Table 1
a
The molalities were calculated by the compiler.
Table 1
b
The solid phases are: A=Na
2
HPO
4
·12H
2
O; B=NaNH
4
HPO
4
·4H
2
O; C=(NH
4
)
2
HPO
2
.
Method/Apparatus/Procedure:
Conventional measurements were made on aliquots of saturated solutions. The ammonium salt was determined gravimetrically as ammoniumtetraphenyl borate
1
and the total salt content was determined by evaporation to constant weight in vacuum over H
2
SO
4
. The sodium salt was then estimated by difference. The composition of the eutonics was determined by an isopiestic method.
2
Source and Purity of Materials:
The AR grade phosphates were recrystallized once from water. The Na
2
HPO
4
was dried at 105 °C. The (NH
4
)
2
HPO
4
was dried in vacuum over sulfuric acid at room temperature.
Estimated Errors:
Solubility: No information is given.
Temperature: No information is given.
References:
1
A. I. Vogel, Quantitative Inorganic Analysis, Wiley, New York, p. 566 (1961).2. R. F. Platford, Amer. J. Sci.
272
, 959 (1972).