IUPAC-NIST Solubility Database
NIST Standard Reference Database 106

Glass Ball as Bullet Solubility System: Carbon dioxide with Diammonium salt of 2-hydroxy-1,2,3-propanetricarboxylic acid and Water

   (1) Diammonium salt of 2-hydroxy-1,2,3-propanetricarboxylic acid; (NH4)2C6H6O7; [3012-65-5]  NIST Chemistry WebBook for detail
   (2) Carbon dioxide; CO2; [124-38-9]  NIST Chemistry WebBook for detail
   (3) Water; H2O; [7732-18-5]  NIST Chemistry WebBook for detail

Original Measurements:
   Lloyd, R., AEC Accession No. 8890, Rep. No. WAPD-TM-511, 1965, 10 pp., Chem. Abstr. 1966, 65, 12910a.

   Temperature = 299.8 K to 333.2 K
   Pressure = 299.8 K to 333.2 K
   Concentration = c2/mol L-1 = 0 - 0.053

Prepared By:
   H.L. Clever

Experimental Remarks:

   The author distinguished between fixed CO2, assumed to be in the form of bicarbonate and carbonate ion, and unfixed CO2, assumed to be in the form of CO2(aq) and H2CO3(aq).

The author found that the fixed dissolved carbon dioxide did not vary with temperature while the unfixed dissolved carbon dioxide decreased as temperature increased. He summarized these results in the following table.

The carbon dioxide solubilities in water correspond to mole fraction solubilities of 5.83 x 10-4 and 3.02 x 10-4 at one atm assuming the density of water and the CO2 saturated solutions have the same value.

Experimental Data:   (Subscripts 1,2,3, ..., in column headings refer to components 1,2,3, ...)

Solubility of carbon dioxide in water and 0.053 mol L-1 ammonium citrate (a).
T/KTemp NotePressure [atm]Pressure [atm]Concentration C1 [mol/L]Concentration NoteConcentration C2 [mol/L]pHpH Note
299.82b0.966-31.2, 0, 31.2 (Total, Fixed, Unfixed)d04.2c
299.82b0.9260.03420.4, 4.2, 16.2d0.0534c
299.82b0.926-26.0, 4.7, 21.3d0.0535c
299.82b0.926-40.0, 5.1, 34.9d0.0536c
301.93b0.926-58.5, 5.8, 52.7d0.0537c
301.93b0.935-23.2, 0, 23.2d04.2c
301.93b0.8950.06520.7, 5.2, 15.5d0.0535c
322.04b0.884-17.8, 0, 17.8d04.2c
322.04b0.8440.11618.6, 5.1, 13.5d0.0535c
333.15b0.804-13.3, 0, 13.3d04.2c
333.15b0.7640.19615.8, 4.0, 11.8d0.0534c
333.15b0.764-17.5, 4.4, 13.1d0.0535c
333.15b0.764-23.8, 5.0, 18.8d0.0536c
333.15b0.764-35.7, 6.0, 29.7d0.0537c
T/KChemical NameConcentration C1 [mol/L atm]
299.8NH4-citr. pH 44.1, 17.5 (Fixed CO<2>, Unfixed CO<2>)
299.8NH4-citr. pH 54.9, 23.0
299.8NH4-citr. pH 65.1, 37.7
299.8NH4-citr. pH 75.9, 54.6
299.8Water0, 32.3
333.2NH4-citr. pH 44.1, 15.5
333.2NH4-citr. pH 54.9, 17.1
333.2NH4-citr. pH 65.1, 24.6
333.2NH4-citr. pH 75.9, 38.9
333.2Water0, 16.5
   a  The common name of the electrolyte is diammonium citrate.
   b  Added by the compiler. The Kelvin temperatures are not intended to represent an accuracy, but to reproduce the Fahrenheit temperatures.
   c  The pH given for water (c2/mol L-1 = 0) means pH of water saturated with carbon dioxide. According to the author the measurements showed that saturating water with CO2 under the ambient barometric pressure in the temperature range of 80 to 140 °F yielded a pH of 4.2 ± 0.1.

The ammonium citrate solutions of certain pH's were prepared as follows:
At pH 4 the solution was prepared from an equimolar mixture of citric acid and diammonium citrate to contain 11.1 g/L of monoammonium citrate, and its pH was adjusted upward to pH 4 by adding ammonia.
At pH5 the solution was primarily diammonium citrate and was prepared by dissolving 12 g of diammonium citrate per liter.
At pH 6 and at pH 7 ammonia was added to the pH 5 solution. At pH 7 the salt was in the form of triammonium citrate.
All solutions were initially prepared to contain 12 g diammonium citrate per liter (0.053 mol L-1).
   d  The values for the solubility of CO2 in water are at a total pressure of 1 atm (101.3 kPa). The carbon dioxide in ammonium citrate solutions was measured at a barometric pressure of 730 mmHg (0.960 atm or 97.3 kPa).

   Two 100mL samples of the solvent were saturated with carbon dioxide by passing pure cylinder CO2 through the solutions for 30 minutes. One sample was used to determine total CO2. It was treated with ammonia and barium chloride to precipitate the total CO2 as barium carbonate which was recovered and treated with acid to liberate the CO2. The other sample was stripped of unfixed CO2 by heating strongly under reduced pressure until the solution volume was reduced in half. The fixed CO2 remaining was treated with ammonia and barium chloride and the barium carbonate recovered and treated with acid to recover the Co2. The unfixed CO2 = Total CO2 - Fixed CO2.
Compiler's note: The 30 minute saturation time seems too short to attain saturation.

Source and Purity of Materials:
   (1) Carbon dioxide. Described as pure cylinder gas, source not given.
   (2) Diammonium citrate. Nothing specified.
   (3) Water. Nothing specified.

Estimated Errors:
   Solubility: Nothing specified.
   Temperature: Nothing specified.