IUPAC-NIST Solubility Database
NIST Standard Reference Database 106

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 Solubility System: Ammonium dihydrogenphosphate with Diammonium hydrogenphosphate, Potassium thiosulfate and Water

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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) Potassium thiosulfate; K2S2O3; [10294-66-3]  NIST Chemistry WebBook for detail
   (4) Water; H2O; [7732-18-5]  NIST Chemistry WebBook for detail

Original Measurements:
   Babenko, A.M.; Andrianov, A.M., Zh. Neorg. Khim. 1984, 29, 2663.

Variables:

   Concentration = Temperature and concentration of K₂S₂O₃ 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-K₂S₂O₃-H₂O system.

t/°C	Chemical1	102 * Mass Fraction w1	Chemical2	102 * Mass Fraction w2	m2(b)	Chemical3	102 * Mass Fraction w3	m3(b)	Chemical4	102 * Mass Fraction w4	m4(b)	Chemical5	102 * Mass Fraction w5	Solid Phase(s)(c)
-21.5	mixture (a)	0	NH4H2PO4	0	0	(NH4)2HPO4	0	0	K2S2O3	52.0	5.69	H2O	48.0	A + B
-21.6	mixture	5.0	NH4H2PO4	2.3	0.45	(NH4)2HPO4	2.7	0.45	K2S2O3	50.0	5.84	H2O	45.0	"
-22.5	mixture	11.2	NH4H2PO4	5.2	1.04	(NH4)2HPO4	6.0	1.0	K2S2O3	44.0	5.16	H2O	44.8	A + C
-27.5	mixture	16.0	NH4H2PO4	7.4	1.3	(NH4)2HPO4	8.6	1.3	K2S2O3	33.6	3.50	H2O	50.4	"
-21.6	mixture	19.2	NH4H2PO4	8.9	1.7	(NH4)2HPO4	10.3	1.73	K2S2O3	36.0	4.22	H2O	44.8	"
-15.4	mixture	24.0	NH4H2PO4	11.2	1.83	(NH4)2HPO4	12.8	1.83	K2S2O3	22.8	2.25	H2O	53.2	"
-23.0	mixture	8.0	NH4H2PO4	3.7	0.69	(NH4)2HPO4	4.3	0.69	K2S2O3	45.0	5.03	H2O	47.0	A + B + C
-17.0	mixture	27.3	NH4H2PO4	12.7	2.18	(NH4)2HPO4	14.6	2.18	K2S2O3	22.0	2.28	H2O	50.7	A + C + D
-8.6	mixture	38.6	NH4H2PO4	22.2	3.14	(NH4)2HPO4	26.4	3.14	K2S2O3	0	0	H2O	61.4	A + D
-13.0	mixture	36.0	NH4H2PO4	16.8	2.53	(NH4)2HPO4	19.2	2.53	K2S2O3	6.4	0.58	H2O	57.6	"
-14.2	mixture	32.0	NH4H2PO4	14.9	2.38	(NH4)2HPO4	17.1	2.38	K2S2O3	13.6	1.31	H2O	54.4	"
39.0	mixture	61.0	NH4H2PO4	28.4	6.33	(NH4)2HPO4	32.6	6.33	K2S2O3	0	0	H2O	39.0	C + D
19.0	mixture	47.0	NH4H2PO4	21.9	4.05	(NH4)2HPO4	25.1	4.05	K2S2O3	6.0	0.67	H2O	47.0	"
10.0	mixture	36.12	NH4H2PO4	16.82	2.931	(NH4)2HPO4	19.30	2.931	K2S2O3	14.0	1.47	H2O	49.88	"
10.0	mixture	42.55	NH4H2PO4	19.81	3.447	(NH4)2HPO4	22.74	3.447	K2S2O3	7.5	0.79	H2O	49.95	"
-1.0	mixture	6.6	NH4H2PO4	3.1	0.64	(NH4)2HPO4	3.5	0.64	K2S2O3	51.37	6.422	H2O	42.03	B + C
12.0	mixture	5.0	NH4H2PO4	2.3	0.53	(NH4)2HPO4	2.7	0.53	K2S2O3	57.0	7.88	H2O	38.0	"

Part 2. Solubility isotherms in the NH₄H₂PO₄-(NH₄)₂HPO₄-K₂S₂O₃-H₂O system.

t/°C	Chemical1	102 * Mass Fraction w1	Chemical2	102 * Mass Fraction w2	m2(b)	Chemical3	102 * Mass Fraction w3	m3(b)	Chemical4	102 * Mass Fraction w4	m4(b)	Chemical5	102 * Mass Fraction w5	Solid Phase(s)(c)
-10	mixture (a)	28.0	NH4H2PO4	13.0	1.75	(NH4)2HPO4	15.0	1.75	K2S2O3	7.2	0.58	H2O	64.8	A
-10	mixture	21.0	NH4H2PO4	9.8	1.3	(NH4)2HPO4	11.2	1.34	K2S2O3	15.8	1.31	H2O	63.2	"
-10	mixture	15.36	NH4H2PO4	7.15	1.01	(NH4)2HPO4	8.21	1.01	K2S2O3	23.2	1.98	H2O	61.44	"
-10	mixture	6.9	NH4H2PO4	3.2	0.45	(NH4)2HPO4	3.7	0.45	K2S2O3	31.0	2.62	H2O	62.1	"
-10	mixture	25.0	NH4H2PO4	11.6	1.93	(NH4)2HPO4	13.4	1.93	K2S2O3	22.5	2.25	H2O	52.5	C
-10	mixture	18.96	NH4H2PO4	8.83	1.73	(NH4)2HPO4	10.13	1.734	K2S2O3	36.8	4.37	H2O	44.24	"
-10	mixture	11.0	NH4H2PO4	5.1	1.0	(NH4)2HPO4	5.9	1.0	K2S2O3	44.5	5.25	H2O	44.5	"
-10	mixture	36.4	NH4H2PO4	16.9	2.57	(NH4)2HPO4	19.5	2.57	K2S2O3	6.36	0.584	H2O	57.24	D
-10	mixture	32.6	NH4H2PO4	15.2	2.44	(NH4)2HPO4	17.4	2.44	K2S2O3	13.4	1.30	H2O	54.0	"
-10	mixture	9.0	NH4H2PO4	4.2	0.80	(NH4)2HPO4	4.8	0.80	K2S2O3	45.5	5.25	H2O	45.5	B
-10	mixture	0	NH4H2PO4	0	0	(NH4)2HPO4	0	0	K2S2O3	55.0	6.42	H2O	45.0	"
0	mixture	27.0	NH4H2PO4	12.6	2.14	(NH4)2HPO4	14.4	2.14	K2S2O3	21.9	2.25	H2O	51.1	A
0	mixture	23.1	NH4H2PO4	10.7	1.73	(NH4)2HPO4	12.3	1.73	K2S2O3	23.0	2.24	H2O	53.9	"
0	mixture	38.0	NH4H2PO4	17.7	2.76	(NH4)2HPO4	20.3	2.76	K2S2O3	6.2	0.58	H2O	55.8	D
0	mixture	33.6	NH4H2PO4	15.6	2.56	(NH4)2HPO4	18.0	2.56	K2S2O3	13.2	1.30	H2O	53.2	"
0	mixture	18.78	NH4H2PO4	8.74	1.73	(NH4)2HPO4	10.04	1.734	K2S2O3	37.4	4.48	H2O	43.82	C
0	mixture	11.0	NH4H2PO4	5.1	1.0	(NH4)2HPO4	5.9	1.0	K2S2O3	45.0	5.37	H2O	44.0	"
0	mixture	9.4	NH4H2PO4	4.4	0.84	(NH4)2HPO4	5.0	0.84	K2S2O3	45.3	5.25	H2O	45.3	"
0	mixture	4.8	NH4H2PO4	2.2	0.44	(NH4)2HPO4	2.6	0.44	K2S2O3	51.2	6.11	H2O	44.0	B
0	mixture	0	NH4H2PO4	0	0	(NH4)2HPO4	0	0	K2S2O3	57.4	7.08	H2O	42.6	"
10	mixture	29.4	NH4H2PO4	13.7	2.41	(NH4)2HPO4	15.7	2.41	K2S2O3	21.18	2.25	H2O	49.42	C
10	mixture	18.0	NH4H2PO4	8.4	1.5	(NH4)2HPO4	9.6	1.5	K2S2O3	32.8	3.50	H2O	49.2	"
10	mixture	10.96	NH4H2PO4	5.10	1.01	(NH4)2HPO4	5.86	1.01	K2S2O3	45.2	5.42	H2O	43.84	"
10	mixture	4.82	NH4H2PO4	2.24	0.450	(NH4)2HPO4	2.58	0.450	K2S2O3	51.8	6.27	H2O	43.38	B
10	mixture	0	NH4H2PO4	0	0	(NH4)2HPO4	0	0	K2S2O3	60.0	7.88	H2O	40.0	"

Notes:
   Table 1  ^a  "Mixture" is an equimolar mixture of NH₄H₂PO₄ and (NH₄)₂HPO₄.
   Table 1  ^b  The molalities were calculated by the compiler. The units are: mol kg^–1
   Table 1  ^c  The solid phases are: A=ice; B=K₂S₂O₃; C=NH₄H₂PO₄; D=(NH₄)₂HPO₄.
   Table 2  ^a  "Mixture" is an equimolar mixture of NH₄H₂PO₄ and (NH₄)₂HPO₄.
   Table 2  ^b  These molalities were calculated by the compiler. The units are: mol kg^–1
   Table 2  ^c  The solid phases are: A=ice; B=K₂S₂O₃; C=NH₄H₂PO₄; D=(NH₄)₂HPO₄.

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

Source and Purity of Materials:
   Chemically pure or reagent grade salts were recrystallized twice and dried at 30 °C. The material designated "mixture" was prepared by mixing equimolar amounts of NH₄H₂PO₄ and (NH₄)₂HPO₄ and homogenizing by grinding in a mortar. Potassium thiosulfate (p., TU 6-09-44-70) was recrystallized twice and dried at 105 °C.

Estimated Errors:

   Temperature: Precision of temperature measurement was ± 0.4 K.

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

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