IUPAC-NIST Solubility Database
NIST Standard Reference Database 106

---

 Solubility System: Ammonium dihydrogenphosphate with Diammonium hydrogenphosphate, Sodium dihydrogenphosphate and Water

---

Components:
   (1) Ammonium dihydrogenphosphate; NH4H2PO4; [7722-76-1]  NIST Chemistry WebBook for detail
   (2) Diammonium hydrogenphosphate; (NH4)2HPO4; [7783-28-0]  NIST Chemistry WebBook for detail
   (3) Sodium dihydrogenphosphate; NaH2PO4; [7558-80-7]  NIST Chemistry WebBook for detail
   (4) Water; H2O; [7732-18-5]  NIST Chemistry WebBook for detail

Original Measurements:
   Babenko, A.M.; Vorob'eva, T.A., Zh. Prikl. Khim. (Leningrad) 49, 1502-6 (1976).

Variables:

   Concentration = Temperature and concentration of NaH₂PO₄ in a mixture containing a mol ratio of NH₄H₂PO₄/(NH₄)₂HPO₄ = 1.

Prepared By:
   J. Eysseltová

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

Part 1. Points of simultaneous crystallization of two or three solid phases in the NH₄H₂PO₄-(NH₄)₂HPO₄-NaH₂PO-H₂O system.

t/°C	Chemical1	102 * Mass Fraction w1	m1(c)	Chemical2	102 * Mass Fraction w2	Chemical3	102 * Mass Fraction w3	Chemical4	102 * Mass Fraction w4	m4(c)	Chemical5	Solid Phase(s)(d)
-8.6	mixture (a)	38.6	2.54	NH4H2PO4	17.97	(NH4)2HPO4	20.63	NaH2PO4	0.00	0.00		A + C
-8.4	mixture	32.0	2.11	NH4H2PO4	14.90	(NH4)2HPO4	17.10	NaH2PO4	6.8	0.92		A + C
-8.4	mixture	20.4	1.29	NH4H2PO4	9.50	(NH4)2HPO4	10.90	NaH2PO4	15.92	2.08		A + C
-9.4	mixture	9.8	0.63	NH4H2PO4	4.56	(NH4)2HPO4	5.24	NaH2PO4	27.06	3.57		A + C
-8.0	mixture	21.25	1.35	NH4H2PO4	9.89	(NH4)2HPO4	11.36	NaH2PO4	15.0	1.96		A + C
-9.0	mixture	16.0	1.01	NH4H2PO4	7.45	(NH4)2HPO4	8.55	NaH2PO4	20.0	2.60		A + C
-11.0	mixture	6.8	0.45	NH4H2PO4	3.16	(NH4)2HPO4	3.63	NaH2PO4	32.0	4.36		A + C
+0.5	mixture	6.0	0.43	NH4H2PO4	2.79	(NH4)2HPO4	3.21	NaH2PO4	37.6	5.55		A + B + C
-8.8	mixture	0.0	0.0	NH4H2PO4	0.0	(NH4)2HPO4	0.0	NaH2PO4	33.5	4.20		A + B
-12.0	mixture	2.4	0.17	NH4H2PO4	1.12	(NH4)2HPO4	1.28	NaH2PO4	40.0	5.79		A + B
19.2	mixture	8.0	0.64	NH4H2PO4	3.72	(NH4)2HPO4	4.28	NaH2PO4	41.4	6.82		B + C
25.2	mixture	8.0	0.70	NH4H2PO4	3.72	(NH4)2HPO4	4.28	NaH2PO4	46.0	8.33		B + C
35.0	mixture	9.8	0.96	NH4H2PO4	4.56	(NH4)2HPO4	5.24	NaH2PO4	48.708	9.78		B + C + D
39.0	mixture	61.0	6.33	NH4H2PO4	28.40	(NH4)2HPO4	32.60	NaH2PO4	0.0	0.0		C + D
45.6	mixture	56.0	5.72	NH4H2PO4	26.07	(NH4)2HPO4	29.93	NaH2PO4	4.4	0.92		C + D
48.3	mixture	48.0	4.67	NH4H2PO4	22.34	(NH4)2HPO4	25.65	NaH2PO4	10.4	2.08		C + D
44.6	mixture	36.0	3.25	NH4H2PO4	16.76	(NH4)2HPO4	19.24	NaH2PO4	19.2	3.57		C + D
50.3	mixture	28.0	2.62	NH4H2PO4	13.04	(NH4)2HPO4	14.96	NaH2PO4	28.8	5.55		C + D
56.0	mixture	24.0	2.27	NH4H2PO4	11.17	(NH4)2HPO4	12.83	NaH2PO4	33.2	6.46		C + D
55.0	mixture	20.0	2.02	NH4H2PO4	9.31	(NH4)2HPO4	10.69	NaH2PO4	40.0	8.33		C + D
67.0	mixture	20.0	2.20	NH4H2PO4	9.31	(NH4)2HPO4	10.69	NaH2PO4	43.2	9.78		C + D
40.2	mixture	0.0	0.0	NH4H2PO4	0.0	(NH4)2HPO4	0.0	NaH2PO4	56.0	10.60		B + E
43.5	mixture	1.8	0.17	NH4H2PO4	0.84	(NH4)2HPO4	0.96	NaH2PO4	55.0	10.61		B + E
46.0	mixture	4.75	0.45	NH4H2PO4	2.21	(NH4)2HPO4	2.54	NaH2PO4	52.5	10.23		B + E
42.0	mixture	8.0	0.82	NH4H2PO4	3.72	(NH4)2HPO4	4.28	NaH2PO4	52.44	11.04		D + E
50.5	mixture	8.0	0.88	NH4H2PO4	3.72	(NH4)2HPO4	4.28	NaH2PO4	55.2	12.50		D + E
49	mixture	8.9	1.01	NH4H2PO4	4.14	(NH4)2HPO4	4.76	NaH2PO4	55.5	12.99		D + E + F
57.2	mixture	0.0	0.0	NH4H2PO4	0.0	(NH4)2HPO4	0.0	NaH2PO4	60.8	12.92		E + F
59.8	mixture	1.6	0.17	NH4H2PO4	0.74	(NH4)2HPO4	0.86	NaH2PO4	60.0	13.02		E + F
63.5	mixture	4.2	0.45	NH4H2PO4	1.96	(NH4)2HPO4	2.24	NaH2PO4	58.0	12.78		E + F
68.4	mixture	11.25	1.35	NH4H2PO4	5.24	(NH4)2HPO4	6.01	NaH2PO4	55.0	13.58		E + F

Part 2. Solubility isotherms in the NH₄H₂PO₄-(NH₄)₂HPO₄-NaH₂PO₄-H₂O system.

t/°C	Chemical1	102 * Mass Fraction w1	m1(c)	Chemical2	102 * Mass Fraction w2(b)	Chemical3	102 * Mass Fraction w3(b)	Chemical4	102 * Mass Fraction w4	m4(c)	Chemical5	102 * Mass Fraction w5	Chemical6	102 * Mass Fraction w6
-5	mixture (a)	0.0	0.0	NH4H2PO4	0.0	(NH4)2HPO4	0.0	NaH2PO4	35.4	4.56	H2O	64.6	(N + P2O5)	21.0
-5	mixture	6.7	0.45	NH4H2PO4	3.12	(NH4)2HPO4	3.58	NaH2PO4	33.0	4.56	H2O	60.3	(N + P2O5)	24.5
-5	mixture	12.0	0.79	NH4H2PO4	5.59	(NH4)2HPO4	6.41	NaH2PO4	26.4	3.57	H2O	61.6	(N + P2O5)	24.5
-5	mixture	2.392	0.17	NH4H2PO4	1.11	(NH4)2HPO4	1.28	NaH2PO4	40.2	5.83	H2O	57.408	(N + P2O5)	25.5
-5	mixture	22.0	1.43	NH4H2PO4	10.24	(NH4)2HPO4	11.76	NaH2PO4	15.6	2.08	H2O	62.4	(N + P2O5)	25.6
-5	mixture	33.4	2.25	NH4H2PO4	15.55	(NH4)2HPO4	17.85	NaH2PO4	6.66	0.92	H2O	59.94	(N + P2O5)	28.78
-5	mixture	40.2	2.72	NH4H2PO4	18.71	(NH4)2HPO4	21.48	NaH2PO4	0.0	0.0	H2O	59.8	(N + P2O5)	29.9
0	mixture	0.0	0.0	NH4H2PO4	0.0	(NH4)2HPO4	0.0	NaH2PO4	37.6	5.02	H2O	62.4	(N + P2O5)	22.1
0	mixture	14.0	0.94	NH4H2PO4	6.51	(NH4)2HPO4	7.48	NaH2PO4	25.8	3.57	H2O	60.2	(N + P2O5)	25.5
0	mixture	6.58	0.45	NH4H2PO4	3.06	(NH4)2HPO4	3.52	NaH2PO4	34.2	4.81	H2O	59.22	(N + P2O5)	26.2
0	mixture	2.38	0.17	NH4H2PO4	1.11	(NH4)2HPO4	1.27	NaH2PO4	41.87	6.26	H2O	55.87	(N + P2O5)	26.4
0	mixture	24.4	1.63	NH4H2PO4	11.36	(NH4)2HPO4	13.04	NaH2PO4	15.12	2.08	H2O	60.48	(N + P2O5)	27.1
0	mixture	33.6	2.28	NH4H2PO4	15.64	(NH4)2HPO4	17.96	NaH2PO4	6.64	0.92	H2O	59.76	(N + P2O5)	28.98
0	mixture	42.6	3.00	NH4H2PO4	19.83	(NH4)2HPO4	22.77	NaH2PO4	0.0	0.0	H2O	57.4	(N + P2O5)	31.6
10	mixture	0.0	0.0	NH4H2PO4	0.0	(NH4)2HPO4	0.0	NaH2PO4	42.2	6.08	H2O	57.8	(N + P2O5)	25.0
10	mixture	6.38	0.45	NH4H2PO4	2.97	(NH4)2HPO4	3.41	NaH2PO4	36.2	5.25	H2O	57.42	(N + P2O5)	26.24
10	mixture	19.0	1.36	NH4H2PO4	8.85	(NH4)2HPO4	10.15	NaH2PO4	24.3	3.57	H2O	56.7	(N + P2O5)	28.63
10	mixture	29.0	2.06	NH4H2PO4	13.50	(NH4)2HPO4	15.50	NaH2PO4	14.18	2.08	H2O	56.72	(N + P2O5)	29.9
10	mixture	2.28	0.17	NH4H2PO4	1.06	(NH4)2HPO4	1.22	NaH2PO4	44.8	7.05	H2O	52.992	(N + P2O5)	28.29
10	mixture	40.0	3.00	NH4H2PO4	18.62	(NH4)2HPO4	21.38	NaH2PO4	6.0	0.92	H2O	54.0	(N + P2O5)	33.36
10	mixture	47.0	3.59	NH4H2PO4	21.88	(NH4)2HPO4	25.12	NaH2PO4	0.0	0.0	H2O	53.0	(N + P2O5)	35.0

Notes:
   Table 2  ^a  "Mixture" is an equimolar mixture of NH₄H₂PO₄ and (NH₄)₂HPO₄.
   Table 2  ^b  These values were calculated by the compiler.
   Table 2  ^c  The molalities were calculated by the compiler. The units are: mol kg^–1.
   Table 2  ^d  The solid phases are: A=ice; B=NaH₂PO₄·2H₂O; C=NH₄H₂PO₄; D=(NH₄)₂HPO₄; E=NaH₂PO₄·H₂O; F=NaH₂PO₄.

Method/Apparatus/Procedure:
   An improved polythermic method¹ was used.

Source and Purity of Materials:
   Reagent grade salts were recrystallized and dried. The ammonium salts were dried at 40 °C to 50 °C. The sodium salt was dried at 105 °C. The material designated "mixture" was prepared by mixing equimolar amounts of NH₄H₂PO₄ and (NH₄)₂HPO₄ and homogenizing them by grinding in a mortar.

Estimated Errors:
   Solubility: No information is given.
   Temperature: No information is given.

References:
   ¹Erayzer, L.N.; Kaganskiy, I.M. Zavod. Lab. 1967, 1, 119.

---

Distributed by the Office of Data and Informatics of the National Institute of Standards and Technology (NIST) Material Measurement Laboratory (MML).
Website is owned by NIST (an agency of the U.S. Department of Commerce)

---

Last updated: February 18, 2015 (Created: August 17, 2007)