Components:
(1) Ammonium dihydrogenphosphate,
NH4H2PO4; [7722-76-1]
NIST WebBook
(2) Diammonium hydrogenphosphate,
(NH4)2HPO4; [7783-28-0]
NIST WebBook
(3) Potassium thiosulfate,
K2S2O3; [10294-66-3]
NIST WebBook
(4) Water,
H2O; [7732-18-5]
NIST WebBook
Original Measurements
Babenko, A. M.; Andrianov, A. M.; Zh. Neorg. Khim. 1984, 29, 2663.
Variables:
K2S2O3 in a mixture containing a mole ratio of NH4H2PO4/(NH4)2HPO4 = 1.
Prepared by:
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:
Ambient temperature: Precision of temperature measurement was ±0.4 K.
References
1 Erayzer, L. N.; Kaganskiy, I. M.; Zavod. Lab. 1967, 1, 119.
Experimental Values:
Part 1. Points of simultaneous crystallization of two or three solid phases in the NH4H2PO4-(NH4)2HPO4-K2S2O3-H2O system.
| T (°C) | w1 | w2 | w3 | 100w4 | 100w5 | m2 (mol/kg)b | m3 (mol/kg)b | m4 (mol/kg)b | Phase (s)c |
|---|---|---|---|---|---|---|---|---|---|
| -21.5 | 0.0 | 0.0 | 0.0 | 52.0 | 48.0 | 0.0 | 0.0 | 5.69 | A + B |
| -21.6 | 5.0 | 2.3 | 2.7 | 50.0 | 45.0 | 4.5 x 10-1 | 4.5 x 10-1 | 5.84 | A + B |
| -22.5 | 11.2 | 5.2 | 6.0 | 44.0 | 44.8 | 1.04 | 1.0 | 5.16 | A + C |
| -27.5 | 16.0 | 7.4 | 8.6 | 33.6 | 50.4 | 1.3 | 1.3 | 3.5 | A + C |
| -21.6 | 19.2 | 8.9 | 10.3 | 36.0 | 44.8 | 1.7 | 1.73 | 4.22 | A + C |
| -15.4 | 24.0 | 11.2 | 12.8 | 22.8 | 53.2 | 1.83 | 1.83 | 2.25 | A + C |
| -23.0 | 8.0 | 3.7 | 4.3 | 45.0 | 47.0 | 6.9 x 10-1 | 6.9 x 10-1 | 5.03 | A + B + C |
| -17.0 | 27.3 | 12.7 | 14.6 | 22.0 | 50.7 | 2.18 | 2.18 | 2.28 | A + C + D |
| -8.6 | 38.6 | 22.2 | 26.4 | 0.0 | 61.4 | 3.14 | 3.14 | 0.0 | A + D |
| -13.0 | 36.0 | 16.8 | 19.2 | 6.4 | 57.6 | 2.53 | 2.53 | 5.8 x 10-1 | A + D |
| -14.2 | 32.0 | 14.9 | 17.1 | 13.6 | 54.4 | 2.38 | 2.38 | 1.31 | A + D |
| 39.0 | 61.0 | 28.4 | 32.6 | 0.0 | 39.0 | 6.33 | 6.33 | 0.0 | C + D |
| 19.0 | 47.0 | 21.9 | 25.1 | 6.0 | 47.0 | 4.05 | 4.05 | 6.7 x 10-1 | C + D |
| 10.0 | 36.12 | 16.82 | 19.3 | 14.0 | 49.88 | 2.931 | 2.931 | 1.47 | C + D |
| 10.0 | 42.55 | 19.81 | 22.74 | 7.5 | 49.95 | 3.447 | 3.447 | 7.9 x 10-1 | C + D |
| -1.0 | 6.6 | 3.1 | 3.5 | 51.37 | 42.03 | 6.4 x 10-1 | 6.4 x 10-1 | 6.422 | B + C |
| 12.0 | 5.0 | 2.3 | 2.7 | 57.0 | 38.0 | 5.3 x 10-1 | 5.3 x 10-1 | 7.88 | B + C |
(a) "Mixture" is an equimolar mixture of NH4H2PO4 and (NH4)2HPO4. (b) The molalities were calculated by the compiler. The units are: mol kg-1 (c) The solid phases are: A = ice; B = K2S2O3; C = NH4H2PO4; D = (NH4)2HPO4.
Part 2. Solubility isotherms in the NH4H2PO4-(NH4)2HPO4-K2S2O3-H2O system.
| T (°C) | 100w1 | 100w2 | 100w3 | 100w4 | 100w5 | m2 (mol/kg)b | m3 (mol/kg)b | m4 (mol/kg)b | Phase (s)c |
|---|---|---|---|---|---|---|---|---|---|
| -10.0 | 28.0 | 13.0 | 15.0 | 7.2 | 64.8 | 1.75 | 1.75 | 5.8 x 10-1 | A |
| -10.0 | 21.0 | 9.8 | 11.2 | 15.8 | 63.2 | 1.3 | 1.34 | 1.31 | A |
| -10.0 | 15.36 | 7.15 | 8.21 | 23.2 | 61.44 | 1.01 | 1.01 | 1.98 | A |
| -10.0 | 6.9 | 3.2 | 3.7 | 31.0 | 62.1 | 4.5 x 10-1 | 4.5 x 10-1 | 2.62 | A |
| -10.0 | 25.0 | 11.6 | 13.4 | 22.5 | 52.5 | 1.93 | 1.93 | 2.25 | C |
| -10.0 | 18.96 | 8.83 | 10.13 | 36.8 | 44.24 | 1.73 | 1.734 | 4.37 | C |
| -10.0 | 11.0 | 5.1 | 5.9 | 44.5 | 44.5 | 1.0 | 1.0 | 5.25 | C |
| -10.0 | 36.4 | 16.9 | 19.5 | 6.36 | 57.24 | 2.57 | 2.57 | 5.84 x 10-1 | D |
| -10.0 | 32.6 | 15.2 | 17.4 | 13.4 | 54.0 | 2.44 | 2.44 | 1.3 | D |
| -10.0 | 9.0 | 4.2 | 4.8 | 45.5 | 45.5 | 8.0 x 10-1 | 8.0 x 10-1 | 5.25 | B |
| -10.0 | 0.0 | 0.0 | 0.0 | 55.0 | 45.0 | 0.0 | 0.0 | 6.42 | B |
| 0.0 | 27.0 | 12.6 | 14.4 | 21.9 | 51.1 | 2.14 | 2.14 | 2.25 | A |
| 0.0 | 23.1 | 10.7 | 12.3 | 23.0 | 53.9 | 1.73 | 1.73 | 2.24 | A |
| 0.0 | 38.0 | 17.7 | 20.3 | 6.2 | 55.8 | 2.76 | 2.76 | 5.8 x 10-1 | D |
| 0.0 | 33.6 | 15.6 | 18.0 | 13.2 | 53.2 | 2.56 | 2.56 | 1.3 | D |
| 0.0 | 18.78 | 8.74 | 10.04 | 37.4 | 43.82 | 1.73 | 1.734 | 4.48 | C |
| 0.0 | 11.0 | 5.1 | 5.9 | 45.0 | 44.0 | 1.0 | 1.0 | 5.37 | C |
| 0.0 | 9.4 | 4.4 | 5.0 | 45.3 | 45.3 | 8.4 x 10-1 | 8.4 x 10-1 | 5.25 | C |
| 0.0 | 4.8 | 2.2 | 2.6 | 51.2 | 44.0 | 4.4 x 10-1 | 4.4 x 10-1 | 6.11 | B |
| 0.0 | 0.0 | 0.0 | 0.0 | 57.4 | 42.6 | 0.0 | 0.0 | 7.08 | B |
| 10.0 | 29.4 | 13.7 | 15.7 | 21.18 | 49.42 | 2.41 | 2.41 | 2.25 | C |
| 10.0 | 18.0 | 8.4 | 9.6 | 32.8 | 49.2 | 1.5 | 1.5 | 3.5 | C |
| 10.0 | 10.96 | 5.1 | 5.86 | 45.2 | 43.84 | 1.01 | 1.01 | 5.42 | C |
| 10.0 | 4.82 | 2.24 | 2.58 | 51.8 | 43.38 | 4.50 x 10-1 | 4.50 x 10-1 | 6.27 | B |
| 10.0 | 0.0 | 0.0 | 0.0 | 60.0 | 40.0 | 0.0 | 0.0 | 7.88 | B |
(a) "Mixture" is an equimolar mixture of NH4H2PO4 and (NH4)2HPO4. (b) These molalities were calculated by the compiler. The units are: mol kg-1 (c) The solid phases are: A = ice; B = K2S2O3; C = NH4H2PO4; D = (NH4)2HPO4.
