IUPAC-NIST Solubilities Database

IUPAC-NIST Solubility Database
NIST Standard Reference Database 106

Solubility System: Carbon dioxide with Electrolyte and Water

Components:
   (1) Electrolyte; ; []  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

Evaluator:
   H. Lawrence Clever, Department of Chemistry, Emory University, Atlanta, GA 30322, USA
August 1995

Critical Evaluation:

An Evaluation of the Solubility of Carbon Dioxide in Aqueous Electrolyte Solutions.

The solubility of a gas in an aqueous electrolyte solution often approximates the behavior pointed out by Sechenov over 100 years ago (1,2,4,5). It obeys the equation, (1/c₂)lg (S⁰/S) = k_scc, where S⁰ , S represent the solubility of the gas in pure water and in the aqueous electrolyte solution, respectively , lg is the base 10 logarithm, c₂ is the concentration of the electrolyte, and k_scc, the Sechenov salt effect parameter when both the gas and electrolyte concentrations are in volume units.

Other gas and electrolyte measures lead to slightly different values of the salt effect parameter. The commonly used forms are:

k_scc/L mo1^-1 = (1/(c₂/mo1 L^-1)) 1g (c⁰₁/mo1 L^-1)/(c₁/mo1 L^-1)
k_smm/kg mo1^-1= (1/(m₂/ mo1 kg^-1)) 1g (m⁰₁/mo1 kg^-1)/(m₁/mo1 kg^-1)
k_scx/L mo1^-1 = (1/(c₂/ mo1 L^-1)) 1g (x⁰₁/x₁)
k_cmx/kg mo1^-1 = (1/(m₂/ mo1 kg^-1)) 1g (x⁰₁/x₁)

where subscript 1 represents the nonelectrolyte gas, and subscript 2 the electrolyte.

The gas solubility ratio in pure water and electrolyte solution, c⁰₁/c₁ will be numerically the same using the Bunsen coefficient ratio, a⁰/a, or the Ostwald coefficient ratio, L⁰/L, as well as the mo1 L^-1 ratio. The Molality ratio, m⁰₁/m₁, is the same as the Kuenen coefficient ratio, S⁰/S, or the solvomolality ratio, A⁰/A. The mole fraction ratio, x⁰/x, is the same as the inverse Henry's constant ratio, K_H/K⁰_H, when the Henry's constant is of the form, (K_H/kPa) = (p₁/kPa)/x₁. The gas mo1 fractions are usually calculated treating each electrolyte ion as an entity. A more detailed description of these units and the interconversions among them is in the introductory material of Volume 10 of the Solubility Data Series (47).

A useful graphical test of salt effect data of either a particular worker or to compare different workers data is to put the Sechenov equation in the form:

1gS = 1g S⁰ - k_s c₂

and plot 1g S vs. c₂, the linear slope will be the negative of he salt effect parameter in what ever set of units is used for S and c₂. A number of such figures follow in this evaluation.

Many workers use electrolyte ionic strength instead of volume concentration, and the salt effect parameter is given in electrolyte ionic strength. There are valid reasons to do this, and we have used the ionic strength designation for most systems except 1-1 electrolytes where ionic strength and electrolyte concentration or molality is numerically the same. The conversion of molar units to ionic strength basis requires dividing by the small whole number of one for 1-1 electrolytes, three for 1-2 and 2-1 electrolytes, four for 2-2 electrolytes, six for 1-3 and 3-1 electrolytes and and 15 for 2-3 and 3-2 electrolytes. The solubilities in the mixed electrolyte solutions are plotted as a function of ionic strength. The salt effect parameters in ionic strength are symbolized k_s1(c)c and k_s1(m)m for ionic strength in volume concentration and molality units, respectively.

For electrolytes other than 1 - 1 and for mixtures of electrolytes we have generally used ionic strength in this evaluation. For electrolytes of higher valent ions the equation becomes 1g S = 1g S⁰ - k_s1(c,m)s I(c,m)₂, and for mixed electrolytes 1g S = 1g S⁰ - k_s1(c,m)s I(c,m)_total. Often k_s1(c,m)s = {k_s1(c,m)s2 + • • • + k_sl(c,m)si}, the sum of the individual salt effect parameters 2 to i. I(c,m) means express ionic strength in either volume concentration or molality depending on the data available. The approach was probably first suggested by van Krevelen and Hoffijzer (23).

The evaluator would be among the first to point out the simple Sechenov approach is not the best way to treat salt effect data. However, it is fast and convenient to use and gives a simple common basis for the comparison of the many data we have here. The user of this evaluation should always consult the original paper, when available, to find what approach the original authors used to explain their data. Some other approaches the user may want to consider are discussed by Markham and Kobe (18,19), and by the Japanese school of workers (36, 37, 39, 41, 42, 43) who suggest extensions of the Sechenov equation. More recently workers have started to use the Pitzer equation and examples are Rumpf, Maurer and coworkers (56, 59, 60) and He and Morse (57).

Two or more groups of workers have measured the solubility of carbon dioxide in several of the same aqueous electrolyte solutions. Unfortunately often they report values of the solubility of carbon dioxide in water at 298 K that differs by several percent. The difference makes for some difficulty in comparing their results by a plot of 1g L vs. c₂ as we have used here. There are data on over 100 systems containing either one electrolyte, one electrolyte and a non-aqueous nonelectrolyte or two or more electrolytes with water. In general the data for carbon dioxide solubility in aqueous electrolyte solutions show better consistency than the data for less soluble gases reviewed in previous Solubility Data Series volumes.

The term salt effect means to many the effect of a strong electrolyte on a property, solubility in this evaluation. However, nonelectrolytes often have a similar magnitude effect on a property. This review contains weak electrolytes, some nonelectrolytes in combination with electrolytes, some inorganic substances in colloidal form and some miscelle forming electrolytes in addition to strong electrolytes.

The systems are given in the order of the standard arrangement for inorganic compounds used by the U.S. National Institute of Science and Technology. The NBS (NIST) Table of Thermodynamic Properties (48) gives a recent description of the standard order and the table is a good example of its use. The number before each system is the standard order number for the electrolyte atom of largest order number.

9 (1) carbon dioxide + Hydrofluoric acid [7664-39-3] + Water

Cox and Head (28) measured the solubility of carbon dioxide in 0, 2.5 and 5.0 mo1 L^-1 aqueous HF at 293.02, 298.07, 303.02, and 308.00 K. Partial pressures of CO₂ ranged from 94.64 to 107.00 kPa. Results were reported as Henry constants with units mo1 L^-1 atm^-1. The salt effect parameter is based on two measurements of the solubility at each of the two HF concentrations. There is a small salting in by the HF. The salt effect parameters are in the table below.

Table 1.

	HF Concentration	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂mol L^-1	Parameter	of Slope
		K_sccL mol^-1
293.02	2.5, 5.0	-0.013	0.0007	CH (28)
298.07	2.5, 5.0	-0.0096	0.0018	CH (28)
303.02	2.5, 5.0	-0.0081	0.0008	CH (28)

At 308.00 K measurements were made at only one concentration and no calculation of the salt effect parameter was made. The negative sign on the salt effect parameter means salting in. Recall that HF is a weak acid.

10 (1) Carbon dioxide + Hydrochloric acid [7647-01-0] + Water

Geffcken (6) made seven measurements of the solubility of CO₂ in 0 to 2.18 mo1 L^-1 aqueous HC1 at 288.15 and 298.15 K and atmospheric pressure. Wolf and Krause (12) made several solubility measurements in 0 - 4 vol % HC1 at 293 K. Van Slyke, Sendroy, Hastings and Neill (13) made nine measurements of he solubility of CO₂ in 0.01 to 0.300 mo1 L^-1 HC1 at 311.2 K and atmospheric pressure. Robb and Zimmer (34) made eight measurements of the solubility of CO₂ in 0 to 10 mo1 L^-1 HC1 at 298.15 K and up to three measurements each at 293.15 and 303.15 K and atmospheric pressure. He and Morse (57) made five measurements of the solubility of CO₂ in 0.01 to 3.0 mo1 kg^-1 HC1 at temperatures of 273.2 , 298.2, 323.2, 348.2, and 363.2 K and a total pressure near one atmosphere. The actual carbon dioxide partial pressures were 0.927, 0.954, 0.865, 0.611 and 0.305 bar, respectively at the five temperatures.

The measurements of Wolf and Krause (12) were considered doubtful and were not used. Salt effect parameters were calculated from the other data and are given in Table 2 (next page). Figure 1 (next page) shows 1g a vs.m₂ at 298.15 from the data of Geffkcken, Robb and Zimmer, and He and Morse. The data of He and Morse were converted to Bunsen coefficients using their density and partial pressure values and assuming ideal gas behavior. The data of Geffcken and of Robb and Zimmer show a modest salting-out to about 1.25 mo1 L^-1, then a salting -in as the HC1 concentration increases. The data of He and Morse show a regular salting-out up to 3.0 mol kg^-1 (2.82 mo1 L^-1) HC1 of a magnitude almost as large as the salting out by sulfuric acid at the same molalities. The differences between the data of Geffcken and Robb and Zimmer and of He and Morse are serious. The evaluator prefers the data of Geffcken and of Robb and Zimmer because the solubility of carbon dioxide in other aqueous strong acid (HC1O₄ and H₂SO₄) solutions show similar trends of salting out and salting in (Fig.1), but only further experimental studies can resolve the differences.

Table 2.
HCl Concentration

	HCl Concentration	Salt Effect	Std. Dev	Reference
T/K	Range, c₂/mol L^-1	Parameter	of Slope
		k_scc/L mol^-1
288.15	0.499 – 2.18	0.013	0.002	Gf (6)
298.15	0.0 – 1.25	0.011	0.003	Gf (6)
	0.0 – 1.26	0.014	0.001	RZ (34)
	0.01 – 2.82	0.026	0.001	HM (57)
[	0.0 – 1.26	0.013	0.002	Comb. Gf & RZ]
311.2	0.01 – 0.300	0.023	0.002	VSHN (13)

Fig. 1 He and Morse (57) report their results in mo1 kg^-1 of HC1 and of CO₂. Table 3 (next page) gives values of the salt effect parameter, k_smm/kg mo1^-1, from their data. There is modest salting out over the 0.01 to 3.0 molal HC1 range at all temperatures. Until the discrepancy among the results of the three laboratories (6, 34 and 57) is resolved all the data are classed tentative, but use with caution.

Table 3.

HCl Molality

	HCl Molality	Salt Effect	Std. Dev.	Reference
T/K	Range, m₂/mol kg^-1	Parameter	of Slope
		k_smm/L mol^-1
273.15	0.01 – 3.00	0.017	0.0015	HM (57)
298.15	0.01 – 3.00	0.016	0.0009	HM (57)
323.15	0.01 – 3.00	0.0090	0.0004	HM (57)
348.15	0.01 – 3.00	0.0060	0.0013	HM (57)
363.15	0.01 – 3.00	0.0059	0.0023	HM (57)

10 (2) Carbon dioxide + Perchloric acid [7601-90-3] + water

Markham and Kobe (19) measured the solubility of CO₂ at 12 molalities between 0 and 22.84 mo1kg^-1 HC1O₄ at 298.15 K. The perchloric acid salts in and the Sechenov salt effect show a definite curvature which is slightly different for concentration (mo1 L^-1) and for molal (mo1 kg^-1) unit gas solubility values (Figure 1). Limiting slopes were determined up to molalities of 4.00 and 6.00 HC1O₄. Results are in Table 4 below.

Table 4. HClO4 Molality

	HClO₄ Molality	Salt Effect	Std. Dev.	Reference
T/K	Range, m₂/mol kg^-1	Parameter	of Slope
		k_smc/L mol^-1
		or k_smm/kg mol^-1
298.15	0 – 6.00	-0.0103 (c)	0.0005	MK (19)
	0 – 6.00	-0.0271 (m)	0.0006	MK (19)
	0 – 4.00	-0.0128 (c)	0.0012	MK (19)
	0 – 4.00	-0.0301 (m)	0.0011	MK (19)

14 (1) Carbon dioxide + Sulfuric acid [7664-93-9] + Water

At least seven papers report the solubility of carbon dioxide in aqueous sulfuric acid. Sechenov (2) reports five solubility values for 8.6 to 100 mass % H₂SO₄ at 290 k, Geffcken (6) reports ten solubility values for 1.0 to 7.6 mo1 L^-1 acid at 288.15 and 298.15 K, Christoff (7) reports four solubility values for 0 - 95.6 mass % acid at 293.15 K, Wolf and Krause (12) report five solubility values for 0 to 4 volume percent acid at 293.2 K, Kobe and Williams (16) report solubility values over 0 to 10 mass % acid at 298.15 K, Markham and Kobe (19) report twenty solubility values for 0 to 100 mo1 % acid at 298.15 K and Shchennikova, Devyatykh, and Korshunov (25) report solubility values for 9.25, 30.5, 36.9, 42, 61.6, 77.6, 78.8, and 84.48 mass % acid over the 288 to 350 K temperature interval.

Results of Wolf and Krause (12) were judged doubtful and were not included in the evaluation. The evaluator judges the Markham and Kobe (19) data at 298.15 K to be the most reliable. Their data shows salting out up to 4 mo1 kg ^-1 acid, salting in between 4 and 14 mo1 kg^-1 acid, salting out between about 15 and 38 mo1 kg^-1 acid and then an increasing solubility until the composition reaches pure sulfuric acid. Geffcken's data are usually reliable, however, for this system Geffcken's data do not reproduce the minimum at 4 mo1 kg^-1 found by Markham and Kobe. Geffcken's data appear to merge with Markham and Kobe data as they approach the second minimum (Figure 2). The data of Shchennikova et al. (25) scatter badly and do not resolve the discrepancy, agreeing sometimes with the Markham and Kobe and other times with Geffcken data. The evaluator prefers the data of Markham and Kobe and has drawn the curves in both figures 1 and 2 with respect to their data.

Figure 1 shows 1g Bunsen coefficient vs the sulfuric acid molality up to 20 mo1 kg^-1 at 298.15 K. The Geffcken data are nearly linear from 0 to 10 mo1 kg^-1 acid with a salt effect parameter of k_smc = 0.0107. The Markham and Kobe data are linear to only 2 mo1 kg ^-1 acid with a salt effect parameter of k_smc = 0.0284. The Markham and Kobe result is preferred.

Figure 2 (next page) shows the entire sulfuric acid + water composition range by a plot of 1g Bunsen coefficient vs 0 to 1.00 mass fraction acid at 298.15 and 290 ± 2 K. There are enough independent data at the lower temperature that parallel the Markham and Kobe data at 298.15 K to give confidence in the reliability of the Markham and Kobe data.

Markham and Kobe fitted their data over the 0 to 10 mo1 kg^-1 sulfuric acid range to the equation:

S/S⁰ = 0.0885 m₂ + 1/(1 + 0.2159 m₂)

where S and S⁰ represent the carbon dioxide Kuenen coefficient in acid solution and in pure water, respectively and m₂ the sulfuric acid molality up to 10 mo1 kg^-1 at 298.15 K. The authors' state the maximum error of their equation to be about 1 %.

Fig. 2

18 (1) Carbon dioxide + Nitric acid; [7697-37-2] + Water

Geffcken (6) reports ten solubility values between 0 and 2.5 mo1 L^-1 HNO₃ at both 288.15 and 298.15 K. Onda, Sada, Kobayashi, Kito and Ito (36) report the solubility in water and one solution at 298.15 K. Nitric acid salt in. The salt effect parameters are given below.

Table 5. HClO4 Molality

	HClO₄ Molality	Salt Effect	Std. Dev.	Reference
T/K	Range, m₂/mol kg^-1	Parameter	of Slope
		k_smc/L mol^-1
		or k_smm/kg mol^-1
298.15	0 – 6.00	-0.0103 (c)	0.0005	MK (19)
	0 – 6.00	-0.0271 (m)	0.0006	MK (19)
	0 – 4.00	-0.0128 (c)	0.0012	MK (19)
	0 – 4.00	-0.0301 (m)	0.0011	MK (19)

The combined value at 298.15 K is a recommended value. The others are tentative.

19 (1) Carbon dioxide + ortho-Phosphoric acid [7664-38-2] + Water

Sada, Kito and Ito (39) report six solubility values in 0 - 2.06 mo1 L^-1 aqueous phosphoric acid at 298.15 K. A linear regression gives a salt effect parameter k_scc = 0.0577 L mo1^-1 with a standard deviation about the slope of 0.0032. Van Slyke, Sendroy, Hasings, and Neill (13) measured the solubility of carbon dioxide in 0, 0.150 and 0.300 mo1 L^-1 H₃PO₄ at 311.2 K. The salt effect parameter from their data is (0.0376 ± 0.0031) L mo1^-1. The salt effect parameter is given in the molar concentration unit since it is assumed most of the acid is in an undissociated form. The results are classed as tentative.

18 (2) Carbon dioxide + Ammonium chloride [12125-02-9] + Water

The solubility of carbon dioxide in aqueous ammonium chloride has been measured by Mackenzie (3) at four concentration up to almost 6 mo1 L^-1 NH₄C1 at temperatures of 281, 288, and 295 K, by Sechenov (5) at eight concentrations between 0 and 4.8 mo1 L^-1 NH₄C1 at 288.35 K, by Findlay and Shen (9) at six concentration between 0 and 3.19 mo1 L^-1 NH₄C1at 298.15 K, by Gerecke (35) five concentration between 0 and 5 mo1 L^-1 NH₄C1 at five degree intervals between 288.15 and 333.15 K, by Yasunishi and Yoshida (42) at up to 23 concentration between 0.24 and 5.65 mo1 L^-1 NH₄C1 at temperatures of 288.15, 298.15, and 308.15 K and by Burmakina, Efanov, and Shnet (45) at 11 concentrations between 0 and 1.0 mo1 L^-1 NH₄C1 at 298.15 K. A measurement of Passauer (14) of carbon dioxide in saturated aqueous ammonium chloride at 293.15 K was not used in the evaluation.

Table 6.

NH4Cl Concentration

	NH₄Cl Concentration	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂/mol L^-1	Parameter	of Slope
		_k_scc/L mol^-1
281	1.23 – 2.51	0.0364	0.0062	Mac (3)
288	1.23 – 4.86	0.0124	0.0020	Mac (3)
288.15	0 – 4.2	0.0317	0.0018	YY (42)
	0 – 5.00	0.0319	0.0081	G (35)
288.35	0 – 1.6	0.0316	0.0014	S (5)

295	1.23 – 4.86	0.0217	0.0022	Mac (3)
298.15	0 – 5.65	0.0242	0.0007	YY (42)
	0 – 5.0	0.0266	0.0086	G (35)
	0 – 3.19	0.0289	0.0020	FS (9)
	0 – 1.00	0.0329	0.0131	BES (45)

308.15	0 – 5.0	0.0080	0.0029	G (35)
318.15	0 – 5.0	-0.0069	0.0048	G (35)
328.15	0 – 5.0	-0.0263	0.0114	G (35)

The data of Yasunishi and Yoshida (42) are probably the most reliable. At 298.15 K they report 24 data points over the 0 to 5.65 mo1 L^-1 range of NH₄C1. The data show a definite curvature (see Figure 3 ) and do not extrapolate to a good value of the solubility of carbon dioxide in water. If one uses the nine data between 0.0 and 1.16 mo1 L^-1 one obtains a salt effect parameter 0.0373 with std. dev. of 0.0012 that extrapolates to the carbon dioxide solubility in water. The Findlay and Shen data show a similar trend. If the data between 0 and 0.944 mo1 L^-1 are used the salt effect parameter is 0.0414 with a standard deviation about the slope of 0.0001 and good extrapolation to the solubility of carbon dioxide in water. The two papers are good evidence of a larger salting-out in dilute solution than in over the full range of salt concentration. The data of Burmakina et al. (45) show a pronounced curvature over even the 0 - 1.00 mo1 L^-1 range. Between 0 and 0.005 mo1 L^-1 the salt effect parameter is 1.06 and between 0.25 and 1.00 mo1 L^-1 it is 0.0392. These are interesting results, but until they are confirmed by other workers they are classed doubtful. Yasunishi and Yoshida (42), Findlay and Shen (9) and Sechenov (5) data are classed as tentative with the Yasunishi and Yoshida data preferred.

The data of Mackenzie (3) is doubtful. It shows more scatter and gives smaller salt effect parameters for a given temperature than the results discussed above. The work of Gerecke (35) is difficult to judge. Here, as with other salts, it shows more scatter and salting in at the higher temperatures which is not confirmed for carbon dioxide by other workers. Gerecke's data should be used with caution.

Rumpf, Nicolaisen and Maurer (60) have measured the solubility of carbon dioxide in 4 and 6 mo1 kg^-1 NH₄C1 at six temperatures between 313.14 and 433.10 K and pressures between 0.04 and 9.35 MPa. The results are similar to the results above at lower temperatures and atmospheric pressure. The solubility data were plotted and values of the solubility taken at 5 MPa at four temperatures. Salt effect parameters calculated from the two molalities at 5 MPa are:

The results appear to be consistent with Figures 1 and 2 of the original paper which show a cross over in solubility between 4 and 6 molal salt at 333 K (a change from salting out at low pressure to salting in at high pressure), and a larger salting out at 433 K than at other temperatures. It would be desirable to have the salting in at higher pressures confirmed by additional experimental work. The authors' use of the Pitzer equation to correlate their results is of interest.

Fig. 3

18 (3) Carbon dioxide + Ammonium bromide [12124-97-9] + Water

Gerecke (35) measured the solubility of carbon dioxide in aqueous ammonium bromide at four concentrations between 0 and 2.0 mo1 L^-1 at five degree intervals between 288.15 and 333.15 K. The results show salting in at 0.5 and 1.0 and L^-1 NH₄Br and salting out at 2.0 and mo1 L^-1 at temperatures of 288.15 to 328.15 K. There are no other data to compare with these data so the effect cannot be confirmed. We suggest caution in using the Gerecke data. No salt effect parameters are given from these data.

18 (4) Carbon dioxide + Ammonium sulfate [7783-20-2] + Water

Sechenov (1) measured the solubility of carbon dioxide in aqueous (NH₄)₂SO₄ up to 1.09 mo1 L^-1 at 291.53 K, Gerecke (35) from 0 to 2.0 mo1 L^-1 salt at five degree intervals from 288.15 to 333.15, Yasunishi and Yoshida (42) from 0 to 3.87 and mo1 L^-1 salt at 288.15, 298.15, and 308.15 K, and Rumpf and Maurer (56) at near 2.0 and 4.0 mo1 kg^-1 salt at six temperatures between 333.13 and 433.15 K over a total pressure range of about 0.018 to 9.9 MPa. The Rumpf and Maurer data will be treated separately below.

The data of Yasunishi and Yoshida (42) show a small but well defined curvature on the 1g L vs. c₂ plot. Thus, the Sechenov approach is probably valid to only about 1 mo1 L^-1 (ionic strength 3) of ammonium sulfate. Their data were treated over several concentration ranges in Table 7.

Only the data over the 0 - 1 salt concentration range extrapolate back to the value of the carbon dioxide solubility in pure water. We suspect this is common for many salt solutions, we just do not have reliable data to show the effect for most systems.

Table 7

(NH4)2 SO4 Conc

	(NH₄)₂ SO₄ Conc.	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂/ mol L^-1	Parameter	of Slope
		k_sl_(c)c/L mol^-1
288.15	0 – 0.99	0.0629	0.0009	YY (42)
	0 – 3.35	0.0531	0.0013	YY (42)
	0.99 – 3.35	0.0506	0.0015	YY (42)

298.15	0 – 0.85	0.0609	0.0015	YY (42)
	0 – 3.36	0.0518	0.0012	YY (42)
	1.24 – 3.36	0.0459	0.0020	YY (42)

308.15	0 – 1.01	0.0577	0.0009	YY (42)
	0 – 3.87	0.0487	0.0014	YY (42)
	1.32 – 3.87	0.0430	0.0015	YY (42)

The ionic salt effect parameters are compared in Table 8 from the work of Yasunishi and Yoshida, of Sechenov and of Gerecke.

Table 8.

(NH4)2SO4 Conc

	(NH₄)₂SO₄ Conc.	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂/mol L^-1	Paramater	of Slope
		k_sl(c)c/L mol^-1
288.15	0 – 2.0	0.0541	0.0029	G (35)
	0 – 0.99	0.0629	0.0009	YY (42)

291.53	0 – 1.09	0.0584	0.0013	S (1)

298.15	0 – 2.0	0.0534	0.0033	G (35)
	0 – 0.85	0.0609	0.0015	YY (42)

308.15	0 – 2.0	0.0531	0.0022	G (35)
	0 – 1.01	0.0577	0.0009	YY (42)

318.15	0 – 2.0	0.0513	0.0022	G (35)
328.15	0 – 2.0	0.0530	0.0011	G (35)

The salt effect parameters in ionic strength of Yasunishi and Yoshida and of Sechenov are classed as tentative. The values from Gerecke show more scatter about the regression line and show little temperature dependence. They are also classed at tentative, but should be used with caution.

Rumpf and Maurer (56) made molal solubility measurements of carbon dioxide at about 2.0 and 4.0 mo1 kg^-1 (NH₄) SO₄ up to a total pressure near 9.5 MPa at six temperatures between 313.15 and 433.15 K. The evaluator has interpolated solubility values at total pressures of 2.0, 5.0, and 8.0 MPa at four temperatures and calculated a salt effect parameter based on the slope between the two ammonium sulfate molalities. The results are shown in Table 9 (next page).

Table 9

Table 9.

T/K	P_total/MPa	k_smm/kg mol^-1	k_sl_(m)m/kg mol^-1
313.15	2.0	0.0654	0.0218
	5.0	0.0666	0.0222
	8.0	0.0702	0.0234

353.15	2.0	0.0579	0.0193
	5.0	0.0651	0.0217
	8.0	0.0645	0.0215

393.15	2.0	0.0732	0.0244
	5.0	0.0699	0.0233
	8.0	0.0708	0.0236

433.15	2.0	0.0888	0.0296
	5.0	0.0852	0.0284
	8.0	0.0792	0.0264

The increasing pressure has a relatively small influence on the salt effect parameter. The salt effect parameter appears to increase with increasing temperature that is contrary to observations at lower temperatures and atmospheric pressure. The salt effect parameters were obtained in an approximate way by the evaluator from the data of Rumpf and Maurer. The authors give a detailed discussion of their results which should be consulted by anyone making use of their data.

18 (5) Carbon dioxide + Ammonium chloride [12125-02-9] + Ammonium sulfate [ 7783-20-2] + Water

Yasunishi, Tsuji and Sada (43) measured the solubility of carbon dioxide in aqueous mixed electrolyte of NH₄C1 and (NH₄)₂SO₄ at 298.15 K. The solutions were:

Mole Fraction NH₄C1       0.00 0.25 0.50 0.75 1.00
Ionic Strength
     Fraction NH₄C1     0.00 0.20 0.25 0.50 1.00
Ionic strength Factor 3    2.5 2.0 1.5 1

The ionic strength factor multiplied by the total concentration converts the value to ionic strength.

The evaluator has treated this paper as an entity to itself. Each data set has been fit to a linear equation 1g L vs. c₂. The negative of the slope is taken as the salt effect parameter which has been put on an ionic strength basis by dividing by the ionic strength factor given above. Salt effect parameters have been calculated using the values for pure NH₄C1 and pure (NH₄)SO₄ and the respective ionic strength fractions. Thus, k_a1(c)c(calc) = (Ionic strength fraction NH₄C1)(0.0299) + (Ionic strength fraction (NH₄)₂SO₄)(0.0536). Results at 298.15 K are in Table 10 below. See also Figure 10B following section 100 (10).

The data for pure ammonium chloride and pure ammonium sulfate are from Yasunishi and Yoshida (42), the present authors have selected 7 of 22 values for ammonium chloride and 7 of 11 values for ammonium sulfate from the earlier paper with no indication as to why this selection was made. Other data from the earlier paper may give different results than observed below.

Table 10

Table 10.

Total Concentration	Ionic Strength	Salt Effect Parameter, k_sl_(c)c
Range, (c₂ + c₃)	Fraction, NH₄Cl	Experimental	Calculated
0.25 – 2.87	0.0	0.0536	-
0.28 – 2.81	0.20	0.0488	0.0489
0.33 – 2.67	0.25	0.0465	0.0476
0.25 – 2.86	0.50	0.0397	0.0418
0.38 – 2.82	1.00	0.0299	0.0418

The salt effect parameter for NH₄C1 seems large (see Table 6), a value of 0.0258 gives calculated values of 0.0480, 0.0467, and 0.0397, which are in much better agreement with the experimental values.

18 (6) Carbon dioxide + Ammonium nitrate [6484-52-2] + Water
Sechenov (5) measured the solubility of carbon dioxide in aqueous NH₄NO₃ at 0 to 10.13 mo1 L^-1 at 288.35 K, Gerecke (35) at 0 to 4 mo1 L^-1 at five degree intervals from 288.15 to 328.15 K and Onda, Sada, Kobayashi, Kito and Ito (36) at 0 to 3.63 mo1 L^-1 at 298.15 K. A measurement of carbon dioxide solubility in aqueous saturated ammonium nitrate at 293.15 K by Passauer (14) was not used in the evaluation. Evaluation results are in Table 11 below.

Table 11.

NH4NO3 Conc

	NH₄NO₃ Conc.	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂/mol L^-1	Parameter	of Slope
		k_sl(c)c/L mol^-1
288.15	0 – 4.0	0.0474	0.0017	G (35)

288.35	0 – 10.13	0.0213	0.0006	S (5)

298.15	0 – 4.0	0.0488	0.0024	G (35)
	0 – 3.63	0.0187	0.0025	OSKKI (36)

308.15	0 – 4.0	0.0526	0.0051	G (35)

318.15	0 – 4.0	0.0558	0.0090	G (35)
	0 - 2.0	0.0224	0.0040	G (35)

328.15	0 – 4.0	0.0570	0.0093	G (35)
	0 – 2.0	0.0223	0.0026	G (35)

The values above are classed tentative, but we suggest the values from Gerecke be used with caution. They show high scatter about the regression line and an increase with temperature not ordinarily observed. The value of 0.0187 L mo1^-1 at 298.15 K has been used in later sections to calculate a mixed salt effect parameter with CaC1₂ and BaC1₂ with fair success.

20 (1) Carbon dioxide + Arsenic Trioxide [1327-53-3] + Water
20 (2) Carbon dioxide + Arsenic Pentoxide [1303-28-2] + Water
20 (3) Carbon dioxide + Arsenic Trioxide + Arsenic Pentoxide + Water
20 (4) Carbon dioxide + Arsenic Trioxide + Arsenic Pentoxide + Hydrocholoric acid [7647-01-0] + Water

Robb and Zimmer (34) report carbon dioxide solubility data in the four systems above plus the carbon dioxide + hydrochloric acid + water system discussed earlier (Section 10 (1)). The authors report measurements at 293.15, 298.15, and 303.15 K in three As₂O₃ solutions up to 0.1113 mo1 L^-1 and three As₂O₅ solutions up to 0.1330 mo1 L^-1. They also report measurements in one system containing the two oxides and two systems containing the two oxides and HC1.

There are several inconsistencies in the original paper. No measurements of carbon dioxide solubility in water at 293.15 and 303.15 K are tabulated, but water solubility values at all three temperatures are shown on the figures. Some carbon dioxide solubility values in the mixtures of oxides and HC1 are larger than in pure water, but these are ignored in later data treatment. The authors give salt effect parameters with no statement as to the temperature or the effect of temperature.

The following salt effect parameters were determined from the data assuming a water solubility from the small figures in the paper.

Table 12.

Arsenic Trioxide

	Arsenic Trioxide		Arsenic Pentoxide
T/K	k_smc/kg mol^-1	Std. Dev.	K_smc/kg mol^-1	Std. Dev.
		Slope		Slope
293.15	0.207	0.058	0.132	0.014
298.15	0.196	0.014	0.095	0.012
303.15	0.219	0.016	0.148	0.013

The authors reported salt effect parameters of 0.180 for As₂O₃ and 0.129 for As₂O₅. The averages of the evaluator's values are 0.207 and 0.125, respectively, assuming no temperature effect. The difference between molality and concentration in these solutions is negligible. The data are classed as tentative.

20 (5) Carbon dioxide + Arsenic Trisulfide [1303-33-9] + Water

Findlay and Creighton (8) measured the solubility of carbon dioxide in four solutions of 0 - 0.0930 mo1 L^-1 As₂S₃ at 298.15 K. The gas pressure ranged from 0.1005 to 0.1707 MPa (754 to 1281 mmHg) without appreciable change in solubility. The salt effect parameter in k_scc = 0.069 ± 0.005 L mo1^-1. The salt effect parameter is about the magnitude one would expect for a molecular solute. The enhanced solubility seen in many colloid systems is not observed. The result is classed tentative.

23 (1) Carbon dioxide + N, N-Dimethylmethanamine hydrochloride [593-81-7] + Water

Gerecke (35) has measured the solubility of carbon dioxide in the N, N-dimethylmethanamine hydrochloride (trimethylamine hydrochloride) at 6 concentrations between 0 and 4 mo1 L^-1 at five degree intervals between 288.15 and 333.15 K. Plots of 1g L vs. c₂ are well-defined smooth curves. The first three points (0, 0.25 and 0.50 mo1 L^-1 salt) and the entire salt concentration range have been fitted to straight lines. The resulting salt effect parameters are in Table 13 below.

Table 13

Table 13.

	C₃H₁₀NCl Conc.	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂/mol L^-1	Parameter	of Slope
		k_sl_(c)c/L mol^-1
288.15	0 – 0.50	0.068	0.013
	0 – 4.0	0.0210	0.0034	G (35)

298.15	0 – 0.50	0.085	0.032
	0 – 4.0	0.0154	0.0056	G (35)

308.15	0 – 0.50	0.118	0.048
	0 – 4.0	0.0194	0.0069	G (35)

318.15	0 – 0.50	0.145	0.0145
	0 – 4.0	0.0199	0.0084	G (35)

328.15	0 – 0.50	0.182	0.057
	0 – 4.0	0.0198	0.0107	G (35)

The increase in the salt effect parameter with temperature in the 0 - 0.50 mo1 L^-1 salt concentration range is contrary to most other observations, so too is the salt effect parameter for the entire salt concentration range which goes through a minimum value. The values are classed as tentative. The system is briefly mentioned in the carbon dioxide in aqueous nonelectrolytes volume.

23 (2) Carbon dioxide + N, N, N-Trimethylmethanaminium iodide [75-58-1] + Water

Gerecke (35) has measured the solubility of carbon dioxide in the N, N, N-trimethyl-methanaminium iodide (tetramethylamonium iodide) at concentrations of 0, 0.1 and 0.19 mo1 L^-1 at five degree intervals between 288.15 and 333.15 K. At the lower temperature the solubility data show salting in at 0.10 mo1 L^-1 and salting out at 0.19 mo1 L^-1 which does not seem likely. Salt effect parameters are calculated and given below at ten-degree intervals between 298.15 and 328.15 K, temperatures at which both salt concentrations show salting out.

Table 14

Table 14.

	C₄H₁₂NI Conc.	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂/mol L^-1	Parameter	of Slope
		k_sl_(c)c/L mol^-1
298.15	0 – 0.19	0.085	0.038	G (35)
308.15	0 – 0.19	0.167	0.090	G (35)
318.15	0 – 0.19	0.258	0.073	G (35)
328.15	0 – 0.19	0.370	0.115	G (35)

The results above are out of the ordinary in that they increase rapidly with increasing temperature and that they are of an unusually large magnitude for a 1-1 electrolyte. Past experience with inert gases is that tetra alkyl ammonium salts salt-out little or even salt-in. Carbon dioxide interacts with water and that may in some way account for the different behavior. There are no other data to compare with these. They are classed as tentative, but use the caution until confirmed. The system is also briefly discussed in the carbon dioxide in aqueous nonelectrolytes value.

23 (3) Carbon dioxide + Ammonium citrate [3012-65-5] + Water

Lloyd (33) measured the solubility of carbon dioxide in water and in 0.053 mo1 L^-1 aqueous ammonium citrate solutions adjusted to pH of 4, 5, 6, and 7 between 299.8 and 333.2 K. The citrate ion ranged from -1 anion, -2 anion and -3 anion at pH's of 4, 5, and 7, respectively. At 299.8 K carbon dioxide was salted out at pH 4 and 5 and salted in a pH 6 and 7. At 333.2 K carbon dioxide was salted in at all pH's. The evaluator suggests the user refer to the data sheet and original paper. No salt effect parameters were calculated by the evaluator. The data are classed as tentative.

24 (1) Carbon dioxide + silicic acid [1343-98-2] + Water
Findlay and Creighton (8) and Findlay and Williams (10) report carbon dioxide solubility in this system. Findlay and Creighton report measurements in four solutions from 0 to 0.466 mo1 L^-1 H₄SiO₄ at 298.15 K and pressures between 0.0975 and 0.1805 MPa (731 and 1354 mmHg). To the evaluator the change in solubility with pressure appears to be within experimental error. Findlay and Williams report measurements in four solutions from 0 to 0.208 mo1 L^-1 acid at 298.15 K and pressures between 0.0.0349 to 0.1020 MPa (262 to 765 mmHg). In this set of experiments there is a definite decrease in Ostwald solubility between the lowest and second lowest (ca. 0.052 MPa) gas pressure. The system "salts in" slightly. The values in the tables below are classed tentative.

Table 15.

H4SiO4 Conc

	H₄SiO₄ Conc.	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂/mol L^-1	Parameter	About Slope
		k_scc/kg mol^-1
298.15	0.0 – 0.466	-0.0085	0.0035	FC (8)
298.15	0.0 – 0.208	-0.0020	0.0008	FW (10)
298.15	0.0 – 0.466	-0.0087	0.0035	Combined (8)(10)

Suspensions in water of colloidal silica, SiO₂ have negligible effect on the solubility of carbon dioxide (8, 10).

29 (1) Carbon dioxide + Aluminum oxide [1333-84-2] + Water

The solubility of carbon dioxide was measured in three dilute solutions of hydrated aluminum oxide at 293.15, 303.15, and 313.15 K by Shkol'nikova (27). The nature of these solutions is not known. The evaluator has calculated salt effect parameters on the basis of 0.0098, 0.0345 and 0.0414 moles of A1₂O₃ per kilogram of water. Carbon dioxide is salted out with salt effect parameters that have a magnitude about that observed for 1-1 electrolytes.

Table 16.

Al2O3 Molality

	Al₂O₃ Molality	Salt Effect	Std. Dev.	Reference
T/K	Range, m₂/mol kg^-1	Parameter	About Slope
		k_smc/kg mol^-1
293.15	0.0098 – 0.0414	0.153	0.086	Sh (27)
303.15	0.0098 – 0.0414	0.103	0.064	Sh (27)
313.15	0.0098 – 0.0414	0.100	0.063	Sh (27)

Measurements in such dilute solutions are difficult. The results are classed tentative, but they should be used with caution.

29 (2) Carbon dioxide + Aluminum chloride [7446-70-0] + Water

Yasunishi and Yoshida (42) measured the solubility of carbon dioxide at six concentrations between 0 and 2.57 mo1 L^-1 A1C1₃ at 298.15 K. Multiplication by 6 converts the concentrations to ionic strength. The ionic strength basis salt effect parameter is k_s1(c)c = 0.0411 L mo1^-1 with a standard error about the slope of 0.0004. The result is classed as tentative. Kobe and Williams (16) made measurements in water and in 25 mass % (2.32 mo1 L^-1) at 298.15 K. The two points give an ionic strength salt effect parameter of 0.0380 which is in reasonable agreement with the Yasunishi and Yoshida result.

29 (3) Carbon dioxide + Aluminum sulfate [10043-01-3]

Yasunishi and Yoshida (42) measured the solubility of carbon dioxide at five concentrations between 0 and 0.85 mo1 L^-1 A1₂(SO₄)₃ at 298.15 K. Multiplication by 15 converts the concentrations to ionic strength. The ionic strength basis salt effect parameter is k_sl(c)c = 0.0504 L mo1^-1 with a standard error about the slope of 0.0008. The result is classed tentative. Kobe and Williams (16) made measurements in water and 20 mass % (0.717 mo1 L^-1) at 298.15 K. The ionic strength salt effect parameter from the two points is 0.0531 which is within reasonable agreement with the Yasunishi and Yoshida result.

33 (1) Carbon dioxide + Zinc chloride [7646-85-7] + Water

Passauer (14) measured the solubility of carbon dioxide in saturated zinc chloride at 293.15 K. No salt effect parameter was calculated because of uncertainty of the solubility of zinc chloride in water. Kobe and Williams (16) measured the solubility of carbon dioxide in 50 mass % (7.34 mo1 kg^-1; 5.74 mo1 L^-1) ZnC1₂ at 298.15 K. The salt effect parameters are k_sl(m)c = 0.0149 and k_sl(c)c = 0.0191. The results are classed tentative.

33 (2) Carbon dioxide + Zinc sulfate [7733-02-0] + Water

Sechenov (5) measured the solubility at five concentrations between 0 and 2.48 mo1 L^-1 ZnSO₄ at 288.35 K. Multiplication of 4 converts the concentrations to ionic strength. The ionic strength salt effect parameter is k_s1(c)c = 0.0691 with standard deviation about the slope of 0.0009. The result is classed as tentative.

36 (1) Carbon dioxide + Copper (II) sulfate [7758-98-7] + Water

Nahoczky (15) reported a single measurement of the solubility of carbon dioxide in saturated aqueous copper sulfate at 288.15 K. Vazquez, Chenlo and Pereira (61) measured the solubility of carbon dioxide in five solutions between 0 and 1.002 mo1 L^-1 CuSO₄ at 298.15 K and 0.1013 MPa. Vazquez, Chenlo, Pereira and Peaguda (64) measured the solubility of carbon dioxide in four solutions between 0.251 and 1.002 mo1 L^-1 CuSO₄ at five degree intervals between 293.1 and 313.1 K at a pressure of 0.1013 MPa.

No salt effect parameter was calculated from Nahoczky's data because of uncertainty in the saturation concentration of the copper sulfate. Ionic strength salt effect parameters were calculated from the Vazquez et al. (61, 64) data. It was assumed the salt concentration values valid at 298.1 K could be used at the other temperatures with negligible error. The concentration salt effect parameters will be four times larger than the values in the table below.

Table 17

Table 17.

	CuSO₄ Concentration	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂/mol L^-1	Parameter	About Slope
		k_sl_(c)c/L mol^-1
293.1	0.251 – 1.002	0.0595	0.0007	VCPP (64)

298.1	0.0 – 1.002	0.0650	0.0029	VCP (61)
	0.251 – 1.002	0.0601	0.0011	VCPP (64)

303.1	0.251 – 1.002	0.0564	0.0038	VCPP (64)
308.1	0.251 – 1.002	0.0585	0.0028	VCPP (64)
313.1	0.251 – 1.002	0.0522	0.0048	VCPP (64)

The Vazquez et al.solubilities show curvature on the 1g L vs. c₂ plot. Much of the curvature comes between 0 and 0.25 mo1 L^-1 salt. The temperature coefficient of the salt effect parameters does not decrease smoothly as expected. The data are classed tentative, but use with caution.

41 (1) Carbon dioxide + Ferric oxide [12259-21-1] + Water

The solubility of carbon dioxide was measured in three dilute solutions of hydrated ferric oxide at 293.15, 303.15 and 313.15 K by Shkol'nikova (27). The nature of these solutions is not known. The evaluator has calculated salt effect parameters on the basis of 0.0063, 0.0315 and 0.0505 moles of Fe₂O₃ per kilogram of water. Carbon dioxide is strongly salted in. Salt effect parameters are below.

Table 18

Table 18.

	Fe₂O₃ Molality	Salt Effect	Std. Dev.	Reference
T/K	Range, m₂/mol kg^-1	Parameter	About Slope
		k_smc/kg mol^-1
293.15	0.0063 – 0.0505	-0.73	0.02	Sh (27)
303.15	0.0063 – 0.0505	-0.83	0.14	Sh (27)
313.15	0.0063 – 0.0505	-0.63	0.15	Sh (27)

Measurements in such dilute solutions are difficult. The results are classed as tentative., but they should be used with caution.

41 (2) Carbon dioxide + Iron hydroxide oxide [20344-33-7], [1309-33-7] + Water

Gatterer (11) measured the solubility of carbon dioxide in six solutions of 0 to 0.322 mo1 L^-1 Fe(OH)₃ at five degree intervals between temperatures of 278.12 and 298.15 K. The author reported eq L^-1, the evaluator has used mo1 L^-1. The carbon dioxide solubility is enhanced by the presence of the colloidal solution. However, the 1g L vs. c₂ plot is curved with slope decreasing as the iron compound concentration increases. Both Findlay and Creighton (8) and Findlay and Williams (10) report carbon dioxide solubilities in Fe(OH)₃ solutions at 298.15 K. The first paper reports solubilities at pressures between 0.0995 and 0.1808 MPa (746 and 1356 mmHg) and the second paper at pressures between 0.0311 and 0.0995 MPa (233 and 746 mmHg). At the higher-pressure range the Ostwald solubility appears to be independent of pressure, at the lower pressure range there is a noticeable decrease in Ostwald solubility as the pressure increases. The solubility at the common pressure of about 0.0995 MPa differs by 7 to 12% in the two experiments. These differences may be due to variations in the colloidal nature of these systems.

The evaluator has used only the first three points of Gatterer (0, 0.0237 and 0.0480 mo1 L^-1 Fe(OH)₃) to determine the initial salt effect parameter. The values are in Table 19. The Findlay and Creighton data over the higher pressure range showed much less salting in than the data at 0.0995 MPa from the Findlay and Williams paper. The nature of these colloidal solutions depends on method of preparation, aging and other treatment. It appears difficult to obtain solutions of the same stoichimetric concentration and reproducible properties.

Table 19

Table 19.

	Fe(OH)₃ Conc.	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂/mol kg^-1	Parameter	About Slope
		k_scc/kg mol^-1
278.12	0.0 – 0.0480	-0.700	0.011	Ga (11)
283.10	0.0 – 0.0480	-0.813	0.014	Ga (11)
288.11	0.0 – 0.0480	-0.875	0.016	Ga (11)
293.13	0.0 – 0.0480	-0.960	0.003	Ga (11)
298.15	0.0 – 0.0480	-1.071	0.068	Ga (11)
298.15	0.0 – 0.1554	-0.273	0.007	FC (8)
298.15	0.0 – 0.1179	-0.701	0.022	FW (10)

41 (3) Carbon dioxide + Ferrous ammonium sulfate [7783-85-9] + Water

Findlay and Shen (9) measured the solubility of carbon dioxide at four concentrations between 0 and 0.573 mo1 L^-1 (NH₄)₂SO₄FeSO₄ (dissolved as the hexahydrate at 298.15 K. Multiplication by 7 converts the concentration to ionic strength. The electrolyte salts in. The molar salt effect parameter is -0.442 with a standard deviation about the slope of 0.004, the ionic strength salt effect parameter is k_s1(c)c = -0.0632 L mo1^-1 with a standard error about the slope of 0.0005. The values are classed as tentative.

41 (4) Carbon dioxide + Ferriferrocyanide {other names: Iron(III)hexacyanoferrate(II) and Iron (3 +) hexacyanoferrate (4-), also Prussian Blue} [14038-43-8]], [12240-15-2] + Water

Gatterer (11) has measured the solubility of carbon dioxide in six solutions between 0 and 0.0747 mo1 L^-1 Fe₄[Fe(CN)₆]₃ at five degree intervals between temperatures 278.12 and 298.15 K. The original paper gives the concentrations as equivalents per liter, the equivalent being 1/12 the molecular weight. The solution is described as colloidal. The salt effect parameters are given on a molar basis since the nature of the solution is not known. The solutions show salting in, but the solubility goes through a maximum and then decreases to a value near the value in water at the highest concentration (0.896 eq L^-1 , 0.0747 mo1 L^-1). The 1g L vs. c₂ plots are linear over only the first three concentrations, and the salt effect parameters are based on the initial slope defined by those three points (0, 0.0105 and 0.0148 mo1 L^-1).

Table 20

Table 20.

	Fe₄Fe(CN)₆]₃	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂/mol kg^-1	Parameter	About Slope
		k_scc/kg mol^-1
278.12	0.0 – 0.0148	-0.526	0.013	Ga (11)
283.10	0.0 – 0.0148	-0.644	0.046	Ga (11)
288.11	0.0 – 0.0148	-0.752	0.023	Ga (11)
293.13	0.0 – 0.0148	-0.841	0.013	Ga (11)
298.15	0.0 – 0.0148	-0.937	0.029	Ga (11)

The results are classed as tentative.

ALKALINE EARTH METAL SALTS

A number of measurements have been made on the solubility of carbon dioxide in aqueous solutions of alkaline earth metal salts. An interesting set of values is the Sechenov salt effect parameters for the alkaline earth chlorides at 298.15 K. Values for k_s1(c)c and R_i, the cation crystallographic radii (63), are given below:

k_s1(c)c/L mo1^-1 Cation 10¹⁰ R_i/m Coordination number MgC1₂ 0.0581 ± 0.0005     Mg²⁺    0.72 6
CaC1₂ 0.0626 ± 0.0008     Ca²⁺ 1.12 8
SrC1₂ 0.065 ± 0.004        Sr²⁺ 1.26 8
BaC1₂ 0.0715 ± 0.0006     Ba²⁺ 1.42 8

Thus, salting out of carbon dioxide by the alkaline earth chlorides increases as the size of the divalent alkaline earth cation increases. These and other salt effect parameters are evaluated below.

93 (1) Carbon dioxide + Magnesium chloride [7786-30-3] + Water

The system was studied by Yasunishi and Yoshida (42) at 288.15, 298.15, and 308.15 K, by Kobe and Williams (16) in water and 30 mass % (3.92 mo1 L^-1) MgC1₂, and in saturated aqueous MgC1₂ by Nahoczky (15) at 288.15 K and by Passauer (14) at 293.15 K. In addition He and Morse (57) at 273.15, 298.15, 323.15, 348.15, and 363.15 using molality units. The work from references (42) and (16) is considered the most useful, but the two data sets are treated separately because one is in mo1 L^-1 units and the other in mo1 kg^-1 units. The ionic strength salt effect parameters from the data of Yasunishi and Yoshida (42) are:

T/K 288.15 298.15 308.15
k_s1(c)c/L mo1^-1 0.0637 0.0581 0.0547
Std. dev. Slope 0.0019 0.0005 0.0008

The salt effect parameters, which decrease with increasing temperature as expected, are classed as tentative. The two points of Kobe and Williams (16) give a salt effect parameter of 0.0595 at 298.15 K that agrees well with the Yasunishi and Yoshida (42) result. The saturated solution data were not treated because of uncertainty in the saturated MgC1₂ concentration.

The salt effect parameters from the data of He and Morse are in Table 21 next page.

Table 20

Table 21.

	MgCl₂ Molality	Salt Effect	Std. Dev.	Reference
T/K	Range, m₂/mol kg^-1	Parameter	of Slope
		k_sl_(m)m/kg mol^-1
273.15	0.1 – 5.0	0.0565	0.0017	HM (57)
298.15	0.1 – 5.0	0.0455	0.0043	HM (57)
323.15	0.2 – 5.0	0.0236	0.0032	HM (57)
348.15	0.1 – 5.0	0.0090	0.0007	HM (57)
363.15	0.1 – 5.0	0.0094	0.0002	HM (57)

The He and Morse data show somewhat more scatter than do the Yasunishi and Yoshida data. The values at 348.15 and 363.15 do not seem to carry the same temperature dependence as the lower temperature values. The data set is classed tentative until more information becomes available.

93 (2) Carbon dioxide + Magnesium sulfate [7487-88-9] + Water

The system was studied by Sechenov (5) at 288.35 K, Markham and Kobe (18) at 273.35, 298.15 and 313.15 K, Gerecke (35) at 5 degree intervals between 288.15 and 333.15 K, Yasunishi and Yoshida (42) at 298.15 K, Nahoczky (15) in aqueous saturated magnesium sulfate and He and Morse (57) at five temperatures between 273.15 and 363.15 K. The ionic strength salt effect parameters from the first four workers are given in Table 22.

The value in [ ] at 298.15 K is a recommended value from the combined data of Markham and Kobe and of Yasunishi and Yoshida. The values of Gerecke show fair standard deviation of the slope, but they show very little change with temperature, thus they are classed doubtful. The other values are classed tentative. The concentration range can be changed to an ionic strength range by multiplication by four.

Table 20

Table 22.

	MgSO₄ Concentration	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂/mol L^-1	Parameter	of Slope
		k_sl_(c)c/L mol^-1
273.35	0.0 – 1.96	0.0788	0.0009	MD (18)

288.15	0.0 – 2.0	0.0717	0.0038	G (35)
288.35	0.0 – 2.617	0.0701	0.0005	S (5)

298.15	0.0 – 1.96	0.0673	0.0007	MK (18)
	0.0 – 2.0	0.0718	0.0020	G (35)
	0.118 – 2.274	0.0669	0.0007	YY (42)

[298.15	0.0 – 2.27	0.0671	0.0004	MK & YY]

313.15	0.0 – 2.7	0.0625	0.0011	MK (18)
	0.0 – 2.0	0.0729	0.0028	G (35)

323.15	0.0 – 2.0	0.0724	0.0032	G (35)
328.15	0.0 – 2.0	0.0724	0.0042	G (35)

The data of He and Morse (57) are reported as molal values for both salt and gas. They report CO₂ solubility values up to 4.0 molal MgSO₄ but the 1g m₁ vs. m₂ lines do not extrapolate well to the solubility value in water. Use of only the first three data point extrapolate better, but the standard deviation about the slope is little changed except for the 273 K Slope. The salt effect parameters are in Table 23 (next page).

99 (5) Carbon dioxide + Ammonium chloride [12125-02-9] + Sodium chloride [7647-14-5] + Water

Yasunishi, Tsuji and Sada (43) measured the solubility of carbon dioxide in the mixed electrolyte of 0.0, 0.25, 0.50, 0.75 and 1.00 mole fraction NaCl at 298.15 K. There were eight or nine solutions at each mole fraction. The NH₄C1 values were a selection of the 23 solubility values of Yasunishi and Yoshida (42) and the NaCl values were from the same source (42). The ionic strength salt effect parameters are in Table 42.

The experimental and the calculated salt effect parameters agree well assuming additivity of the salt effects. See also Figure 11A following section 100 (10).

Table 41

Table 42.

Ionic Strength	Ionic Strength	Salt Effect	Salt Effect	Difference
Ratio	Range	Parameter,^a	Parameter,
NaCl/NH₄Cl	l_tot/mol L^-1	k_sl_(c)c/L mol^-1	Calculated
0.00/1.00	0 – 5.48	0.0252	-
0.25/0.75	0 – 5.05	0.0424	0.0436	2.8 %
0.50/0.50	0 – 5.18	0.0588	0.0620	5.4 %
0.75/0.25	0 – 5.28	0.0786	0.0803	2.2 %
1.00/0.00	0 – 5.10	0.0987	-

99 (6) Carbon dioxide + Ammonium nitrate [6484-52-2] + Sodium chloride [7647-14-5] + Water

Onda, Sada, Kobayashi, Kito and Ito (37) measured the solubility of carbon dioxide in mixed electrolyte of 0.335, 0.500 and 0.635 mole fraction NaCl at 298.15 K. There were five to seven solutions at each mole fraction. To test the additivity of the salt effects salt effect parameters of 0.0995 and 0.0187 were used for NaCl and NH₄NO₃, respectively.

Table 41

Table 43.

Ionic Strength	Ionic Strength	Salt Effect	Salt Effect	Difference
Ratio	Range	Parameter,^a	Parameter,
NaCl/NH₄NO₃	l_tot/mol L^-1	k_sl_(c)c/L mol^-1	Calculated
0.335/0.665	0 – 2.97	0.0412	0.0458	11 %
0.50/0.50	0 – 2.78	0.0551	0.0591	7.3 %
0.635/0.365	0 – 3.05	0.0657	0.0701	6.7 %

The salt effects are not additive. All results are classed as tentative. See also Figure 11B following sections 100 (10).

99 (7) Carbon dioxide + Magnesium sulfate [7487-88-9] + Sodium chloride [7647-14-5] + Water

Yasunishi, Tsuji and Sada (43) measured the solubility of carbon dioxide in mixed electrolyte of 0.0, 0.25, 0.50, 0.75 and 1.00 mole faction NaCl [0.0, 0.077, 0.260, 0.428 and 1.00 ionic strength fraction NaCl] at 298.15 K. Six solutions were measured at each mole fraction. The results are in the Table 44.

Table 41

Table 44.

Ionic Strength	Ionic Strength	Salt Effect	Salt Effect	Difference
Ratio	Range	Parameter,^a	Parameter,
NaCl/MgSO₄	l_tot/mol L^-1	k_sl_(c)c/L mol^-1	Calculated
0.00/1.00	0 – 9.10	0.0665	-
0.077/0.923	0 – 6.68	0.0683	0.0691	1.2 %
0.260/0.740	0 – 5.46	0.0726	0.0755	4.0 %
0.428/0.572	0 – 3.81	0.0804	0.0863	1.1 %
1.00/0.00	0 – 2.49	0.1010	-

The electrolytes act with near additively. The results are classed tentative. See also Figure 11B following section 100 (10).

99 (8) Carbon dioxide + Calcium chloride [10043-52-4] + Sodium chloride [7647-14-5] + Water

Malinin and Savelyeva (38) measured the solubility of carbon dioxide in water and in one mixture of CaC1₂ and NaCl at a total ionic strength of 2.65 at 298.15 K and 47.95 bar. The solubility in water and in the one solution gives salt effect parameters k_s1(c)m = 0.032 and k_s1(c)c = 0.040. The results are classed tentative.

99 (9) carbon dioxide + Calcium Sulfate [7778-18-9] + Sodium chloride [7647-14-5] + Water

He and Morse (57) measured the solubility of carbon dioxide in six solutions of 0.1 to 6.0 mo1 kg^-1 NaCl and 0.01 mo1 kg^-1 CaSO₄ at temperatures of 273.15, 298.15, 323.15, 348.15 and 363.15 K. In other mixed electrolyte studies the electrolytes have been at some constant ionic strength ratio. In this study the calcium sulfate is near it saturation value at 0.01 mo1 kg^-1 (ionic strength 0.04) in all solutions.

The data were treated to obtain k_s1(m)m/kg mo1^-1 values in the table below.

Table 38

Table 45.

		Ionic Strength	Salt Effect	Std. Dev.	Reference
T/K	p₁/bar	Range	Parameter	of Scope
		l₂/mol kg^-1	k_sl_(m)m/kg mol^-1
273.15	0.979	0.14 – 6.04	0.0866	0.0083	HM (57)
298.15	0.954	0.14 – 6.04	0.0852	0.0024	HM (57)
323.15	0.865	0.14 – 6.04	0.0623	0.0007	HM (57)
348.15	0.611	0.14 – 6.04	0.0286	0.0020	HM (57)
363.15	0.305	0.14 – 6.04	0.0227	0.0011	HM (57)

The results parallel within 0.1 to 4.2 % the results for sodium chloride alone at the first three temperatures. At 348 and 363 K the calcium sulfate containing solutions show higher salt effect parameters by 40 and 16 %, respectively. The results are not reliable enough to draw conclusions about the effect of the calcium sulfate in the mixed electrolyte.

99 (10) Carbon dioxide + Ammonium nitrate [6484-52-2] + Barium chloride [10361-37-2] + Sodium chloride [7647-14-5] + Water

Onda, Sada, Kobayashi, Kito and Ito (37) measured the solubility of carbon dioxide in five solutions of a mixed electrolyte of NH₄NO₃/BaC1₂/NaC1 of mole ratio 3/1/3 which is ionic strength ratio 1/1/1. A plot of 1g L vs I₂, over the 0 - 0.633 ionic strength range gives the salt effect parameter of k_s1(c)c = 0.0612 with a standard error about the regression line of 0.0010. A calculated salt effect parameter obtained by summing one third values of each pure electrolyte salt effect parameter gives 0.0632 that is 3.3 % larger than the experimental value. The result is classed as tentative.

99 (11) Carbon dioxide + Sodium chloride [7647-14-5] + Glucose [50-99-7] + Water

Yuan and Yang (58) measured the solubility of carbon dioxide in six solutions of 0 to 3.00 mo1 kg^-1 sodium chloride in a 15 mass % glucose-water mixture at ten degree intervals between 278.15 and 318.15 K. The salt effect parameters on a molality basis are in Table 46.

Table 20

Table 46.

	NaCl Concentration	Salt Effect	Std. Dev.	Reference
T/K	Range, m₂/mol kg^-1	Parameter	of Slope
		k_smm/kg mol^-1
278.15	0 – 3.00	0.086	0.007	YuYa (58)
288.15	0 – 3.00	0.064	0.011	YuYa (58)
298.15	0 – 3.00	0.063	0.099	YuYa (58)
308.15	0 – 3.00	0.048	0.008	YuYa (58)
318.15	0 – 3.00	0.042	0.004	YuYa (58)

The data show more than an average amount of scatter on the lg m₁ vs. m₂ plot. Our values of the salt effect parameter differ from the author's values especially at temperatures of 288 and 308 K. The results show smaller magnitude salt effect parameters in the glucose solution than in pure water. The data are classed as tentative.

99 (12) Carbon dioxide + Sodium chlorate [7775-09-9] + Water

Sechenov (5) measured the solubility of carbon dioxide at four concentrations between 0 and 6.57 mo1 L^-1 NaC1O₃ at 288.35 K. The salt effect parameter is k_scc = 0.0874 L mo1^-1 with a standard error of the slope of 0.0020. The value is classed tentative.

99 (13) Carbon dioxide + Sodium perchlorate [7601-89-0] + Water

Gerecke (35) measured the solubility of carbon dioxide at five concentrations between 0 and 1.6 mo1 L^-1 NaClO₄ at five degree intervals between the temperatures of 288.15 and 333.15 K. The salt effect parameters are below.

Table 20

Table 47.

	NaClO₄ Concentration	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂/mol L^-1	Parameter	of Slope
		k_scc/kg mol^-1
288.15	0 – 1.6	0.103	0.006	G (35)
298.15	0 – 1.6	0.110	0.012	G (35)
308.15	0 – 1.6	0.125	0.015	G (35)
318.15	0 – 1.6	0.156	0.022	G (35)
328.15	0 – 1.6	0.190	0.022	G (35)

It is important to point out that the trend more commonly seen for inorganic gases that do not have a special interaction with water in aqueous electrolytes is a small salt effect parameter that decreases with increasing temperature. The relatively large salt effect parameter that increases with temperatures is unusual. The results are classed as tentative, but use with caution until confirmed by other workers.

99 (14) Carbon dioxide + Sodium bromide [7647-15-6] + Water

Sechenov (5) measured the solubility of carbon dioxide at four concentrations between 0 and 6.71 mo1 L^-1 NaBr at 288.35 K. Rosenthal (24b) measured the solubility at five concentrations between 0 and 7.08 mo1 L^-1 at 293.15 K. Gerecke (35) measured the solubility at five concentrations between 0 and 4.50 mo1 L^-1 at five degree intervals between temperatures of 288.15 and 333.15 K. Salt effect parameters from these papers are compared in Table 48 (next page). Vazquez, Chenlo, Pereira and Peaguda (64) measured the solubility at seven concentrations between 0.389 and 2.72l mo1 L^-1 NaBr at 298.1 K and 0.1013 MPa. In an earlier paper (61) they reported the solubility of carbon dioxide in water at the same conditions of temperature and pressure. Their (61, 64) values of the salt effect parameter fitted with and without the solubility in water are in Table 48.

This is one of only a few systems for which the salt effect parameters from the data of Gerecke show the expected magnitude and temperature coefficient. However, the data do show more scatter than the data of Sechenov and Rosenthal. The data of Vazquez et al. (61, 64) show a definite curvature on a lg L vs.c₂ plot with much of the curvature between 0 and 0.4 mo1 L^-1 NaBr. At 298.15 K the solubility values of Vazquez et al. are significantly lower than the values of Gerecke for a given NaBr concentration. [See also Figure 10 following section 100 (7)]. All of the results are classed tentative with a slight preference for the values of Sechenov and Rosenthal at 288.5 and 293.15 K, respectively. At 298.15 K we cannot make a choice between.

Table 20

Table 48.

	NaBr Concentration	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂/mol L^-1	Parameter	of Slope
		k_scc/L mol^-1
288.15	0 – 4.50	0.0875	0.0059	G (35)
288.35	0 – 6.71	0.0981	0.0005	S (5)

293.15	0 – 7.08	0.0874	0.0006	R (24b)
	0 – 4.50	0.0831	0.0044	G (35)

298.15	0 – 4.50	0.0779	0.0041	G (35)
	0 – 2.72	0.0905	0.0043	VCPP (64)
	0.39 – 2.72	0.0842	0.0029	VCPP (64)

308.15	0 – 4.50	0.0709	0.0025	G (35)
318.15	0 – 4.50	0.0680	0.0010	G (35)
328.15	0 – 4.50	0.0520	0.0037	G (35)

99 (15) Carbon dioxide + Sodium iodide [7681-82-5] + Water

Rosenthal (24b) measured the solubility of carbon dioxide at four concentrations between 0 and 6.01 mo1 L^-1 NaI at 293.15 K. Gerecke (35) measured the solubility at five concentrations between 0 and 4.0 mo1 L^-1 at five degree intervals between temperatures of 288.15 and 333.15 K. Salt effect parameters from their data are in the table below.

Table 20

Table 49.

	NaI Concentration	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂/mol L^-1	Parameter	of Slope
		k_scc/L mol^-1
288.15	0 – 4.00	0.0792	0.0033	G (35)

293.15	0 – 6.01	0.0726	0.0023	R (24b)
	0 – 4.00	0.0779	0.0025	G (35)

298.15	0 – 4.00	0.0774	0.0017	G (35)
308.15	0 – 4.00	0.0750	0.0046	G (35)
318.15	0 – 4.00	0.0577	0.0101	G (35)
328.15	0 – 4.00	0.0400	0.0161	G (35)

The results are classed as tentative. There seems little reason to pick one result over the other at 293.15 K. The difference could be due to the smaller NaI concentration range used by Gerecke since with some systems the slope decreases at the higher concentrations (ionic strengths). Gerecke's results at 318.15 and 328.15 K scatter badly and these two results should be used with caution.

99 (16) Carbon dioxide + Sodium hydrogen sulfite [7631-90-5] + Water

Onda, Sada, Kobyashi, Kito and Ito (36) measured the solubility of carbon dioxide at four concentrations between 0 and 2.02 mo1 L^-1 NaHSO₃ at 298.15 K. The salt is not 100 per cent dissociated so the molar concentration salt effect parameter is reported. It is k_scc = 0.1434 L mo1^-1 with a standard deviation of the slope of 0.0031. The result is classed at tentative. If the salt was 100 % dissociated the ionic strength salt effect parameter, k_sl(c)c, would be the value above divided by 3.

99 (17) Carbon dioxide + Sodium sulfate [7757-82-6] + Water

The evaluation of the solubility of carbon dioxide in aqueous solutions for sodium sulfate is divided into three parts. i) Papers reporting measurements at or near atmospheric pressure in which both Na₂SO₄ and CO₂ are reported in mo1 L^-1 or other volume units; ii) papers reporting measurements at or near atmospheric pressure in which both Na₂SO₄ and CO₂ are reported in mo1 kg^-1 or other mass units; and iii) papers which report measurements at high pressures and temperatures regardless of the units used for Na₂SO₄ and CO₂.

i) Sechenov (5) reported the solubility of carbon dioxide in eight solutions from 0 to 2.00 mo1 L^-1 sodium sulfate at 288.35 K, Markham and Kobe (18) reported the solubility of carbon dioxide in five solutions from 0 to 1.435 mo1 L^-1 sodium sulfate at 298.15 and 313.15 K, Shchennikova, Devyatykh and Korshunov (26) reported the solubility of carbon dioxide in six solutions of 0.20 to 1.68 mo1 L^-1 sodium sulfate at one to five temperatures between 298.15 and 348.15 K, Gerecke (35) measured the solubility of carbon dioxide in four solutions between 0 and 1.0 mo1 L^-1 sodium sulfate at five degree intervals between 288.15 and 333.15 K, Onda, Sada, Kobayashi, Kito, and Ito (36) reported the solubility of carbon dioxide in four solutions from 0 to 1.44 mo1 L^-1 sodium sulfate at 298.15 K and Yasunishi and Yoshida (42) reported the solubility of carbon dioxide in up to fifteen solutions from 0 to 2.21 mo1 L^-1 sodium sulfate at 288.15, 298.15 and 308.15 K. The concentrations have been changed to ionic strength by multiplying by 3. The ionic strength salt effect parameters from the papers are given in the table below.

Table 20

Table 50.

	Na₂SO₄ Conc.	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂/mol L^-1	Parameter	of Slope
		k_sl_(c)c/L mol^-1
288.15	0 – 1.00	0.0829	0.0102	G (35)
	0 – 1.06	0.1072	0.0049	YY (42)
288.35	0 – 2.00	0.1063	0.0004	S (5)

298.15	0.2 – 1.68	0.1001	0.0062	SDK (26)
	0 – 1.00	0.0836	0.0132	G (35)
	0 – 1.435	0.0991	0.0006	MK (18)
	0 – 1.44	0.0982	0.0009	OSKKI (36)
	0 – 2.21	0.0981	0.0004	YY (42)
[	0 – 2.2	0.0983	0.0005	(18)(36)(42)
				combined ]

308.15	0 – 1.00	0.0826	0.0188	G (35)
	0 – 1.76	0.0894	0.0009	YY (42)

313.15	0 – 1.435	0.0913	0.0004	MK (18)
318.15	0 – 1.00	0.0869	0.0195	G (35)
323.15	0.42 – 1.68	0.1108	0.0057	SDK (26)
328.15	0 – 1.00	0.0904	0.0199	G (35)

Shchennikova, Devyatykh and Korshunov (26) reported salt effect parameters form their smoothed data on a natural logarithm mo1 fraction basis. The evaluator converted their values to our k_s1(c)x/L mol^-1 values. The results are:

T/K 298 303 313 323 338
K_s1(c)x 0.094 0.097 0.104 0.124 0.221

The values at 298 and 303 K seem reasonable, but the steady increase in salt effect parameter with temperature is contrary to our experience and the values at the higher temperatures are classed doubtful.

Gerecke's (35) data give smaller slopes than other data, show more scatter about the regression line and extrapolate to a carbon dioxide in water value that is 5 to 8.5 % low. The data are classed doubtful.

The combined data of Markham and Kobe (18), Onda et al. (36) and of Yasunishi and Yoshida (42) give a recommended salt effect parameter at 298.15 K of 0.0983 ± 0.0005 L mo1^-1.

Figure 7 shows logarithm of Bunsen coefficient vs. the sodium sulfate ionic strength at 288.15 and 298.15 K and one atm. The data are best fitted by a straight line. The data of He and Morse were converted from their molality values to Bunsen coefficients and concentration ionic strength using their density and partial pressure vales and assuming ideal gas behavior and Henry's law. Their results at 298.15 K deviate considerably from the other 298.15 K values.

ii) He and Morse (57) report the molality solubility of carbon dioxide in 4 or 5 solutions ranging from 0.01 up to 3.00 mo1 kg^-1 sodium sulfate at temperatures of 273.15, 298.15, 323.15, 348.15 and 363.15 K and carbon dioxide partial pressures of 0.305 to 0.979 bar. In addition Markham and Kobe (18) and Gerecke (35) report their data so values of the salt effect parameter , k_s1(m)m, can be obtained. Salt effect parameters from these data are given in Table 51 (next page).

Agreement in Table 51 is not good. The evaluator prefers the values form the data of Markham and Kobe since their results agree well with other reliable workers when mo1 L^-1 units are used.

Na2SO4 Molal

		Na₂SO₄ Molal	Salt Effect	Std. Dev.	Reference
T/K	p₁/bar	Range	Parameter	of Slope
		m₂/mol kg^-1	k_sl_(m)m/kg mol^-1
273.15	0.979	0.01 – 0.3	0.0663	0.0129	HM (57)
	0.979	0.01 – 0.1	0.106	0.065	HM (57)

298.15	0.954	0.1 – 2.0	0.0619	0.0047	HM (57)
	0.954	0.1 – 1.0	0.0654	0.0033	HM (57)
		0 – 1.5	0.0911	0.0016	MK (18)
		0 – 1.05	0.0754	0.0132	G (35)

313.15		0 – 1.5	0.0835	0.0011	MK (18)
		0 – 1.05	0.0776	0.0199	G (35)

323.15	0.865	0.1 – 3.0	0.0287	0.0044	HM (57)
	0.865	0.1 – 1.0	0.0466	-	HM (57)

348.15	0.611	0.1 – 3.0	0.0134	0.0028	HM (57)
	0.611	0.1 – 1.0	0.0295	0.0027	HM (57)

363.15	0.305	0.1 – 3.0	0.0223	0.0006	HM (57)

Fig. 7

iii) Corti, Krenzer, de Pablo and Prausnitz (54) measured the solubility of carbon dioxide in solutions of 0.95 to 2.72 mo1 kg^-1 sodium sulfate at temperatures of 323.15 and 348.15 K and total pressures between 37.9 and 145.1 bar. Rumpf and Maurer (56) measured the solubility of carbon dioxide in two solutions of about 1 and 2 mo1 kg^-1 sodium sulfate at seven temperatures between 313 and 433 K over a total pressure interval of 0.019 to 9.71 MPa.

The evaluator has interpolated data from both papers at several temperatures and pressures. There are really solubility measurements at only two molalities of sodium sulfate. Therefore any salt effect parameters derived from these data are of limited value. The values obtained this way are in the table below.

Table 52

Table 52.

T/K	p_total/MPa	k_smm/kg mol^-1	k_sl_(m)m/kg mol^-1	Reference
313.15	2.0	0.202	0.067	RM (56)
	5.0	0.230	0.077
	8.0	0.232	0.077

323.15	10.0	0.225	0.075	CKPP (54)
348.15	10.0	0.202	0.067	CKPP (54)

353.15	2.0	0.202	0.067	RM (56)
	5.0	0.202	0.067
	8.0	0.208	0.069

393.15	2.0	0.156	0.052	RM (56)
	5.0	0.158	0.053
	8.0	0.168	0.056

433.15	2.0	0.123	0.041	RM (56)
	5.0	0.165	0.055
	8.0	0.163	0.054

The data in these two papers deserve better treatment than we have time to give them in this brief review. The salt effect parameters above should be used between 1.0 and 2.0 molal (3.0 and 6.0 ionic strength) sodium sulfate. The results indicate only a small effect of pressure on salting out and a slight decrease in the salting out as temperature increases.

99 (18) Carbon dioxide + Sulfuric acid [7664-93-9] + Sodium sulfate [7757-82-6] + Water

Kobe and Kenton (17) measured the solubility of carbon dioxide in one solution which was 0.90 molal H₂SO₄ and 1.76 molal Na₂SO₄ at 298.15 K. The total ionic strength is 7.98 mo1 kg^-1. The evaluator used the solubility of carbon dioxide in water from Markham and Kobe (18) to calculate an ionic strength salt effect parameter 0.0609. The value is less than the contribution of sodium sulfate alone in a solution to which it contributes 0.662 fraction ionic strength. The sulfuric acid is contributing an apparent salting in effect. The result is classed tentative. Kobe and Williams (16) measured the solubility in water and in a solution that was 5 volume % H₂SO₄ and 20 mass % Na₂SO₄. The solubility values are classed tentative, but no effort was made to calculate a solubility parameter.

Shchennikova, Devyatykh and Korshuhov (26) measured the solubility of carbon dioxide in solutions which ranged between 0.2 to 1.3 mo1 L^-1 sodium sulfate and 0.24 to 5.66 mo1 L^-1 (2.3 to 42 mass %) sulfuric acid at temperatures between 298.15 and 348.15 K. In all 11 solutions were studied. Assuming 100 % dissociation of both salt and acid and total ionic strength ranged from 1.31 to 18.84 mo1 L^-1. All eleven solutions were studied at 298.15 K and only up to three solutions studied at the other temperatures . At 298.15 K the five data points between ionic strength 3.6 and 6.9 fitted well a Sechenov plot with a salt effect parameter of k_sl(c)c = 0.0993, but the linear portion extrapolated to a water solubility value that was twice its normal value. The salt effect parameter was only 0.016 over the 0 to 3.6 ionic strength range and about 0.01 over the 11.8 to 18.8 ionic strength range. This is a complex system that deserves further analysis.

99 (19) Carbon dioxide + Ammonium sulfate [7783-20-2] + Sodium sulfate [7757-82-6] + Water

Rumpf and Maurer (56) measured the solubility of carbon dioxide in a solution that was 1 molal in (NH₄)₂SO₄ and 1 molal in Na₂SO₄ at six temperatures between 313 and 433 K over a total pressure range of 0.0084 to 9.67 MPa. Thus, the total ionic strength is about 6 mo1 kg^-1. Since we have only a single concentration it is not possible to calculate a salt effect parameter. The solubility data are probably quite good and are classed as tentative.

99 (20) Carbon dioxide + Ammonium nitrate [6484-52-2] + Sodium sulfate [7757-82-6] + Water

Onda, Sada, Kobayashi, Kito and Ito (37) measured the solubility of carbon dioxide in seven solutions of 0 to 2.81 mo1 L^-1 total ionic strength in which the ionic strength ratio of ammonium nitrate and sodium sulfate was 1 at 298.15 K. The salt effect parameter is k_s1(c)c =(0.0557 ± 0.0009) L mo1^-1. The value is 4.8 % less than one would calculate from the pure salt parameters. The value is classed as tentative.

99 (21) Carbon dioxide + Sodium chloride [7647-14-5] + Sodium sulfate [7757-82-6]

Yasunishi, Tsuji, and Sada (43) measured the solubility of carbon dioxide in six solutions with a total concentration of 0 to 2.49 mo1 L^-1 NaC1 + Na₂SO₄ with NaC1 salt mole fraction of 0, 0.25, 0.50, 0.75 and 1.00 at 298.15 K. The ionic strength fractions are NaC1/Na₂SO₄ = 0/1.0, 0.10/0.90, 0.25/0.75, 0.50/0.50 and 1.0/0. The ionic strength salt effect parameters are in the table below (Table 53).

Table 41

Table 53.

Ionic Strength	Ionic Strength	Salt Effect	Std. Dev.	Calc. Salt	Difference
Ratio	Range	Parameter	about slope	Effect Par.	%
NaCl/Na₂SO₄	l₂/mol L^-1	k_sl(c)c/L mol^-1
0/1.0	0 – 6.62	0.0988	0.0006	-
0.10/0.90	0 – 4.36	0.0947	0.0013	0.0990	4.5
0.25/0.75	0 – 4.12	0.0950	0.0010	0.0993	4.5
0.50/0.50	0 – 3.11	0.0985	0.0018	0.0998	1.3
1.0/0	0 – 2.49	0.1007	0.0017	-

The experimental result ranges from 4.5 to 1.3 % less than the result calculated assuming independent action of the electrolytes. The results are classed as tentative. See Figure 11A following section 100 (10).

99 (22) Carbon dioxide + Ammonium chloride [12125-02-9] + Sodium chloride [7647-14-5] + Sodium sulfate [7757-82-6] + Water

Yasunishi, Tsuji and Sada (43) measured the solubility of carbon dioxide in six solutions of five different mole ratios of the three salts; NH₄C1/NaC1/Na₂SO₄ = 0/0.50/0.50, 0.125/0.50/0.375, 0.25/0.50/0.25, 0.325/0.500/0.125, and 0.50/0.50/0 at 298.15 K. Each was fitted to a lg L vs. c₂ line to obtain the salt effect parameters below. The calculated ionic strength salt effect parameters are based on the values for each salt in pure water. There is a small departure from additivity for the mixed electrolyte solutions.

Ionic Strength

Ionic Strength	Ionic Strength	Salt Effect	Std. Dev.	Calc. Salt	Diff.
Ratio	Range	Parameter	about Slope	Effect Par.	%
NH₄Cl/NaCl/Na₂SO₄	l₂/mol L^-1	k_sl(c)c/L mol^-1
0/0.250/0.750	0 – 4.12	0.0950	0.0010	0.0985	3.7
0.071/0.286/0.643	0 – 3.46	0.0901	0.0009	0.0933	3.6
0.167/0.333/0.500	0 – 3.73	0.0844	0.0012	0.0863	2.3
0.300/0.400/0.300	0 – 3.19	0.0724	0.0012	0.0765	5.7
0.500/0.500/0	0 – 3.45	0.0621	0.0015	0.0619	-0.3

99 (23) Carbon dioxide + Sodium thiosulfate [7772-98-7] + Water

Both Passauer (14) and Nahoczky (15) measured the solubility of carbon dioxide in saturated aqueous sodium thiosulfate, the first at 293 K the second at 288 K. The solubility measurements are classed tentative, but no salt effect parameters were calculated fro the data because of uncertainty in the solubility of sodium thiosulfate and concern about the reliability of a salt effect parameter based on just one salt concentration.

99 (24) Carbon dioxide + Sodium nitrate [7631-99-4] + Water

The system was studied by Sechenov (5) at 288.35 K, Markham and Kobe (18) at 273.35 and 298.15 K, Yasunishi and Yoshida (42) at 288.15, 298.15 K and 308.15 K and by Gerecke (35) at five-degree intervals between 288.15 and 333.15 K. In general the results accord well. Gerecke's results show by far the most scatter and largest standard deviation of the slope of 1g L vs c₂ plots. Salt effect parameters are in Table 55 (next page).

Gerecke (35) reports values at 293, 303, 313, 318 and 328 K in addition to his values above. His solubility values scatter much more than the data of the other workers and a simple straight-line slope does not show the expected variation with temperature. The data are classed doubtful.

The values in [ ] in Table 55 (next page) are combined data sets and are recommended. The recommended salt effect parameters are (0.0874 ± 0.0010) at 288.2 K and (0.0777 ± 0.0.0002) at 298.15 K.

Table 55

Table 55.

T/K	Concentration	Salt Effect	Reference
	Range, c₂/mol L^-1	Parameter
		k_scc/L mol^-1
273.35	0 – 6.300	0.0989	MK (18)

288.15	0 – 4	0.0677	G (35)
	0.382 – 5.929	0.0847	YY (42)
288.35	0 – 7.356	0.0891	S (5)

[288.2	0 – 7.356	0.0874	(5) & (42)]

298.15	0 – 6.300	0.0770	MK (18)
	0 – 4	0.0677	G (35)
	0.382 – 7.256	0.0781	YY (42)

[298.15	0 – 7.256	0.0777	(18) & (42)]

308.15	0 – 4	0.0649	G (35)
	0.346 – 5.186	0.0723	YY (42)

323.15	0 – 4	0.0647	G (35)
333.15	0 – 4	0.0649	G (35)

99 (25) Carbon dioxide + Phosphoric acid [7664-38-2] + Sodium dihydrogen phosphate [7558-80-7] + Water

Van Slyke, Sendroy, Hastings and Neill (13) measured the solubility of carbon dioxide in 0.150 and 0.300 mo1 L^-1 H₃PO₄ and in mixtures of 0.0375 to 0.300 mo1 L^-1 NaH₂PO₄ and 0.011 to 0.030 mo1L^-1 H₃PO₄ at 311.2 K. The solubility was corrected for the effect of phosphoric acid, which changed the solubility 0.3 % or less, and the corrected solubility treated as if only the sodium salt was present. The salt effect parameter for the NaH₂PO₄ alone was k_scc = (0.184 ± 0.005) L mo1^-1. See section 19 (1) for the result for phosphoric acid.

99 (26) Carbon dioxide + Sodium Formate [141-53-7] + Water
99 (27) Carbon dioxide + Sodium acetate [127-09-3] + Water

Gerecke (35) reports carbon dioxide solubility data between 0 and 4 mol^-1 sodium formate and 0 and 2 mo1 L^-1 sodium acetate at five degree intervals between 288.15 and 333.15 K. The solubility of carbon dioxide in sodium formate shows salting in at concentration of 0.1, 0.2 and 0.5 mo1 L^-1, salting out at 1 and 2 mo1 L^-1 and salting in at 4 mo1 L^-1. A similar variation is observed in the sodium acetate solutions.

Both formate and acetate ions are the anions of weak acids and thus themselves bases. We would expect an apparent salting in because of the reaction of the basic anions with the acidic carbon dioxide. Reactions

CO₂(aq) + H₂ + HCOO(aq) = HCO₃(aq) + HCOOH(aq)
CO₂(aq) + H₂O + 2 HCOO(aq) = CO₃²(aq) + 2 HCOOH(aq)

contribute to the effect. We have not tried to analyze the data beyond the suggestion of an acid base interaction being responsible for the apparent salting in.

99 (28) Carbon dioxide + Sodium phenoxide [139-02-6] + Water

Kimura and Takeuchi (29) report the solubility of carbon dioxide in aqueous sodium phenoxide as functions of temperature, pressure and electrolyte concentration. The data show the effect of an acid base reaction between the acidic carbon dioxide and the basic phenoxide anion. At 293.15 K there is strong salting in at all concentrations between 0.805 and 3.04 mo1 L^-1 sodium phenoxide which is described by a salt effect parameter of -0.237, at 323.15 the salt effect parameter is -0.40. The salt effect parameters were calculated for the solubility values at 0.98/0.99 atm partial pressure carbon dioxide. The values are classed tentative.

99 (29) Carbon dioxide + Sodium 4-[{4-(dimethylamino)pheynl}azo]benzenesulfonic acid salt (Methyl orange) [547-58-0] + Water

Findlay and Shen (9) measured the solubility of carbon dioxide in dilute solutions of methyl orange at 298.15 K. The evaluator treated the solubility data at 122 - 124 kPa and obtained a salt effect parameter of -3.00 L mo1^-1for the 0.0101 to 0.0281 mo1 L^-1 methyl orange solutions with a standard deviation of the slope of 0.15. The methyl orange salts-in strongly. The result is classed tentative, but use with caution.

99 (30) Carbon dioxide + Lactic acid [50-21-5] + Sodium lactate [920-49-0] + Water

Van Slyke, Sendroy, Hastings and Neill (13) measured the solubility of carbon dioxide in 0.100 to 0.300 mo1 L^-1 lactic acid and in mixtures of 0.150 and 0.300 mo1 L^-1 sodium lactate and 0.100 to 0.300 mo1 L^-1 lactic acid at 311.2 K. The effect for the lactic acid is scattered and small. Its molar parameter is k_scc = (0.006 ± 0.006) L mo1^-1. The lactic acid was assumed to have a negligible effect in the mixture and the data were treated as if sodium lactate alone was present. The resulting salt effect parameter is k_scc = (0.125 ± 0.006) mo1 L^-1. The sodium lactate salts out and the result is classed tentative.

99 (31) Carbon dioxide + Sodium monododecyl sulfuric acid ester (or SDS); [151-21-3] + Water
99 (32) Carbon dioxide + Sodium 1-heptylsulfonate (or SHSo); [22767-50-6] + Water
99 (33) Carbon dioxide + Sodium perfluoro-octanoate (or SPFO);[335-95-5] + Water
23 (4) Carbon dioxide + N,N,N-Trimethyl-1-hexadecanaminium bromide (or CTAB); [57-09-0] + Water
Note: This system belongs with the carbon number, 23. It is better considered here with other micelle forming solutions.

Ownby, Prapaitrakul and King (50) measured the solubility of carbon dioxide in the four systems listed above at either 298.2 or 299.2 K over a small pressure range. The solutions appear to obey Henry's law. At salt concentrations above the critical micelle concentration (CMC) the carbon dioxide is salted in, below the CMC the gas is salted out. The salt CMC's are SDS 0.0081; SPFO 0.032; CTAB 0.00092; and SHSo 0.28 mo1 kg^-1. Only the sodium 1-heptyl sulfonate (SHSo) has a large enough CMC to see the salting out effect (Figure 8 ). Both the salting out and salting in parameter are given for the SHSo, and only salting in parameter are given for the other salts in the table below.

Fig. 8

Table 56

Table 56.

Salt	Molality	Salt Effect	Std. Dev.
	Range, m₂/mol kg^-1	Parameter	of Slope
		k_smm/kg mol^-1
SHSo	0.0 – 0.4	0.091	0.004
	0.6 – 1.2	-0.060	0.003
SDS	0.0 – 0.6	-0.116	0.006
SPFO	0.0 – 0.6	-0.164	0.007
CTAB	0.0 – 0.4	-0.179	0.008

99 (34) Carbon dioxide + Sodium trifluoroacetate [2923-18-4] + Water

Castellani and Berchiesi (62) report one solubility measurement of carbon dioxide in 19.0 mo1 kg^-1 sodium trifluoroacetate at 294.65 K and 0.936 atm of 0.0077 mo1 L^-1. The evaluator estimated a solubility of carbon dioxide in water under these conditions of 0.0353 mo1 L^-1. The two values give a salt effect parameter of k_smc = 0.035. The value is classed tentative, but use with caution.

100 (1) Carbon dioxide + Potassium chloride [7447-40-7] + Water

The system has been studied by Sechenov (5) at 288.35 K, by Geffcken (6) at 288.15 and 298.15 K, by Findlay and Shen (9) at 298.15 K, by Passauer (14) at 293.15 K, by Markham and Kobe (18) at 273.35, 298.15 and 313.15 K, Gerecke (35) at five degree intervals between 288.15 and 333.15 K, by Yasunishi and Yoshida (42) at 298.15 and 308.15 K, by Burmakina, Efanov, and Shnet (45) at 298.15 and by He and Morse (57) at five temperatures between 273.15 and 363.15 K. Each workers data have been fitted to a linear 1g L vs. c₂ line with the exception of He and Morse whose data was fitted to a linear 1g m₁ vs. m₂ line and Passauer (14), whose measurement in saturated aqueous potassium chloride, was not used. The concentration results are below.

Table 20

Table 57.

	KCl Concentration	Salt Effect	Standard	Reference
T/K	Range, c₂/mol L^-1	Parameter	Deviation
		k_scc/L mol^-1	of Slope
273.35	0 – 3	0.0768	0.0017	MK (18)

288.15	0.423 – 1.058	0.0731	0.0022	GF (6)
	0 – 1	0.0817	0.0012	G (35)

288.35	0.0 – 2.564	0.0935	0.0041	S (5)

298.15	0.423 – 1.058	0.0705	0.0029	GF (6)
	0.247 – 1.000	0.0680	0.0052	FS (9)
	0.0 – 3.558	0.0622	0.0015	MK (18)
	0.0 – 2.0	0.0650	0.0029	G (35)
	0.498 – 4.131	0.0569	0.0015	YY (42)
	0 – 0.200	0.0755	0.0119	BES (45)
[298.15	0.0 – 2.0	0.0664	0.0009	All except (45)]

308.15	0 – 2	0.0694	0.0135	G (35)
	0.420 – 4.110	0.0567	0.0011	YY (42)

313.15	0 – 3	0.0597	0.0043	MK (18)
	0 – 2	0.0755	0.0134	G (35)

323.15	0 – 2	0.0776	0.0135	G (35)

333.15	0 – 2	0.0854	0.0214	G (35)

The value at 298.15 in [ ] is based on the 21 values from all papers between 0.0 and 2.0 mo1 L^-1 KCl. It is the only recommended value. A plot of all the data to 4.3 mo1 L^-1 KCl shows a small curvature at concentrations above 2.0 mo1 L^-1 KCl. Gerecke's value at 4.3 mo1 L^-1 is off from the pattern of the other data and is rejected. Burmakina et al. (45) made nine measurements in the 0-0.200 mo1 L^-1 KCl range. Measurements in dilute solutions are difficult and subject to large error [(49) and this volume preliminary material]. Their data scatters badly and their results were not included in the general average of 298.15 K data. The data of He and Morse (57) are treated separately below.

Table 58

Table 58.

		KCl Molality	Salt Effect	Standard	Reference
T/K	p₁/bar	Range, m₂/mol kg^-1	Parameter	Deviation
			k_smm/kg mol^-1	of Slope
273.35	1.049	0.1 – 3.51	0.0403	0.0037	HM (57)
298.15	0.954	0.1 – 4.0	0.0375	0.0072	HM (57)
323.15	0.865	0.1 – 5.0	0.0248	0.0015	HM (57)
348.15	0.611	0.1 – 5.0	0.0174	0.0019	HM (57)
363.15	0.305	0.1 – 5.0	0.0170	0.0013	HM (57)

The values appear to be slightly lower than expected from the other data on the system. They are classed

Figure 9 shows logarithm of Bunsen coefficient vs. the potassium chloride concentration (ionic strength) at 288 and 298 K. Only the data of Gerecke (35) deviates significantly from the other data. The data of He and Morse (57), calculated as Bunsen coefficients from the author's data assuming ideal gas and Henry's law behavior, show more scatter than the other data.

Fig. 9

100 (2) Carbon dioxide + Hydrochloric acid [7647-01-0] + Potassium chloride [7447-40-7] + Water

Van Slyke, Sendroy, Hastings and Neill (13) measured the solubility of carbon dioxide in solutions that were 0.01 mo1 L^-1 in HCl and 0 to 0.300 mo1 L^-1 in KCl at 311.2 K. The very small concentration of HCl was assumed to have a negligible effect on salting out and the data were treated as if KCl alone was present. The result for the KCl is k_scc = (0.0691 ± 0.0032) mo1 L^-1 and it is classed tentative.

100 (3) Carbon dioxide + Calcium chloride [10043-52-4] + Potassium chloride [7447-40-7] + Water

Yasunishi, Tsuji and Sada (43) studied this system at 298.15 K and mole ratios of KCl/CaCl₂ of 0.0/1.00, 0.25/0.75, 0.50/0.50, 0.75/0.25 and 1.00/0.0. As an ionic strength ratio the values are 0.0/1.00, 0.10/0.90, 0.25/0.75, 0.50/0.50 and 1.0/0. The resulting salt effect parameters assuming a linear 1g L vs.l₂ are shown in Table 59 (next page). The calculated values assume the pure KC1 and pure CaCl₂ salt effect parameters are additive as the sum of the products of ionic strength fraction times the salt effect parameter for each electrolyte. See also Figure 11B following section 100 (10).

The pure KC1 and CaC1₂ values in Table 59 do not agree well with values given earlier. Another problem is that the regression lines give solubility in water values that range from 1.4 to 4.1 % low. In spite of these problems, the pure salt effect parameters have been used to calculate the salt effect parameters for the mixtures and the results appear satisfactory. The data deserve a more detailed treatment than we can give it here. They are classed as tentative.

Table 41

Table 59.

Ionic Strength	Concentration	Salt Effect	Salt Effect	Difference
Ratio	Range	Parameter	Parameter,	%
KCl/CaCl₂	c₂/mol L^-1	k_sl_(c)c/L mol^-1	Calculated
1.00/0.00	0.498 – 3.505	0.0605	-	-
0.50/0.50	0.429 – 3.501	0.0586	0.0588	0.3
0.25/0.75	0.512 – 3.401	0.0594	0.0580	2.3
0.10/0.90	0.426 – 3.233	0.0572	0.0574	0.4
0.00/1.00	0.558 – 3.801	0.0571	-	-

100 (4) Carbon dioxide + Sodium chloride [7647-14-5] + Potassium chloride [7447-40-7] + Water

Yasunishi, Tsuji and Sada (43) studied this system at 298.15 K and mole ratios of (same as ionic strength ratios) NaC1/KC1 of 0.0/1.0, 0.25/0.75, 0.50/0.50, 0.75/0.25 and 1.0/0.0. The resulting salt effect parameters assuming a linear 1g L vs. I₂ are below. The calculated values assume the pure NaC1 and pure KC1 salt effect parameters are additive as the sum of the products of mo1 fraction times the salt effect parameter for each electrolyte.

Table 41

Table 60.

Ionic Strength	Concentration	Salt Effect	Salt Effect	Difference
Ratio	Range	Parameter	Parameter,	%
NaCl/KCl	c₂/mol L^-1	k_sl_(c)c/L mol^-1	Calculated
1.00/0.00	0.498 – 3.505	0.0986	-	-
0.75/0.25	0.545 – 4.311	0.0873	0.0882	1.0
0.50/0.50	0.479 – 4.396	0.0766	0.0778	1.6
0.25/0.75	0.537 – 4.125	0.0677	0.0673	-0.6
0.00/1.00	0.498 – 4.131	0.0569	-	-

The mixed electrolyte systems appear to have no specific interaction within experimental error. The data are classed tentative. See Figure 11A following section 100 (10).

100 (5) Carbon dioxide + Calcium chloride [10043-52-4] + Sodium chloride [7647-14-5] + Potassium chloride [7447-40-7] + Water

The system was studied by Yasunishi, Tsuji and Sada (43) at 298.15 K and several ratios of CaC1₂/NaC1/KC1. The salt effect parameters are in the table below.

Table 41

Table 61.

Ionic Strength	Concentration	Salt Effect	Salt Effect	Difference
Ratio	Range	Parameter	Parameter	%
CaCl₂/NaCl/KCl	c₂/mol L^-1	k_sl_(c)c/L mol^-1	Calculated
0.00/0.50/0.50	0.479 – 4.396	0.0766	0.0778	1.6
0.50/0.167/0.333	0.386 – 2.762	0.0643	0.0669	4.0
0.75/0.00/0.25	0.512 – 3.401	0.0580	0.0561	3.3

The calculated salt effect parameter is probably within experimental error of the measured parameter. The values are classed tentative.

100 (6) Carbon dioxide + Potassium bromide [7758-02-3] + Water

Three laboratories report data on the system. Sechenov (5) studied the system at 288.35 K, Geffcken (6) at 288.15 and 298.15 K and Gerecke (35) at ten temperatures between 288.15 and 333.15 K.

The data of both Sechenov and Geffcken at 288 K are linear in 1g L vs. c₂, but the slopes do not agree well . Gerecke's data shows salting in at 4 mo1 L^-1 KBr at temperatures of 298 K and above. Plots of Gerecke's data as 1g L vs. c₂ are linear to either 0 - 1 or 0 - 2 mo1 L^-1 KBr. The slopes do not agree with the values of Sechenov and Geffcken. The salt effect parameter is not a regular increase or decrease with increasing temperature. Gerecke's data are classed doubtful.

The salt effect parameters of Sechenov and Geffcken and a sampling of Gerecke's values are below. Geffcken's values are preferred, but use with caution.

Table 20

Table 62.

	KBr Concentration	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂/mol L^-1	Parameter	of Slope
		k_scc/L mol^-1
288.15	0.550 – 1.064	0.0635	0.0012	Gf (6)
	0.0 – 2.0	0.0499	0.0044	G (35)

288.35	0.0 – 4.228	0.0567	0.0017	S (5)

298.15	0.550 – 1.064	0.0672	0.0030	Gf (6)
	0.0 – 4.0	0.0074	0.0146	G (35)
	0.0 – 2.0	0.0394	0.0080	G (35)
	0.0 – 1.0	0.0602	0.0022	G (35)

303.15	0.0 – 1.0	0.0506	0.0016	G (35)
313.15	0.0 – 1.0	0.117	0.037	G (35)
323.15	0.0 – 1.0	0.150	0.002	G (35)
333.15	0.0 – 1.0	0.136	0.048	G (35)

100 (7) Carbon dioxide + Potassium iodide [7681-11-0] + Water

In addition to the same three workers (5, 6, 35) that report on the KBr systems, Onda, Sada, Kobayashi, Kito and Ito (36) report carbon dioxide solubility measurements at 0, 1 and 2 mo1 L^-1 KI at 298.15 K and 0.1013 MPa, Passauer (14) reports a measurement in saturated aqueous KI at 293.15 K, and Vazquez, Chenlo, Pereira and Peaguda (64) report seven measurements between 0.241 and 1.687 mo1 L^-1 KI at 298.1 K and 0.1013 MPa. In an earlier paper (61) they report the solubility in water at the same temperature and pressure. Passauer's value was not used. At 298.15 K there is fair agreement among the results of Geffcken (6), Gerecke (35) and Onda et al. (36) to 2 mo1 L^-1 KI. The results are classed tentative. The data of Vazquez et al. (64) are about 7 % smaller than the other data for any given KI concentration and their data are classed doubtful. Their data shows a definite curvature which is emphasized more when the water value is used. See also Figure 10 . The salt effect parameters are below.

Table 20

Table 63.

	KI Concentration	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂/mol L^-1	Parameter	of Slope
		k_scc/L mol^-1
288.15	0.559 – 1.119	0.0624	0.0029	Gf (6)

288.35	0.0 – 5.767	0.0516	0.0027	S (5)

298.15	0.559 – 1.119	0.0540	0.0006	Gf (6)
	0.0 – 4.0	0.0208	0.0057	G (35)
	0.0 – 2.0	0.0453	0.0013	G (35)
	0.0 – 1.0	0.0483	0.0017	G (35)
	0.0 – 2.002	0.0520	0.0036	OSK (36)
	0.0 – 1.69	0.0505	0.0081	VCPP (64)
	0.24 – 1.69	0.0375	0.0040	VCPP (64)
	0.0 – 1.0	0.0541	0.0023	(6, 35, 36)

313.15	0.0 – 2.0	0.0581	0.0082	G (35)
323.15	0.0 – 2.0	0.0659	0.0083	G (35)
333.15	0.0 – 2.0	0.0830	0.0119	G (35)

Sechenov's data at 288.35 K are classed tentative although the salt effect parameter is smaller than expected from other data at 288 and 298 K. Gerecke's data at the higher temperatures shows a salting out effect that increases with temperature. This is contrary to normal expectations and the data should be used with caution.

Fig. 10

100 (8) Carbon dioxide + Potassium sulfate [7778-80-5] + Water

Yasunishi and Yoshida (42) measured the solubility of carbon dioxide at four concentrations of potassium sulfate between 0.093 and 0.454 mo1 L^-1 (0.279 and 1.362 ionic strength at 298.15 K. The salt effect parameter as a function of ionic strength is k_sl(c)c = (0.0777 ± 0.0003) L mo1^-1 and it is classed as tentative. Passauer (14) reports the carbon dioxide solubility in saturated aqueous potassium sulfate at 293.15 K. No salt effect parameter was calculated from his measurement.

He and Morse (57) measured the solubility of carbon dioxide in 0.01 to as high as 0.9 mo1 kg^-1 K₂SO₄ at five temperatures between 273.15 and 363.15 K. The carbon dioxide partial pressure was different at each temperature. They reported both salt and gas in molality. Ionic strength salt effect parameters in molality units from their data are in the table below. The values are classed tentative. Multiplication by three will put the salt effect parameters on a molal basis.

Table 64

Table 64.

		K₂SO₄ Molal	Salt Effect	Standard	Reference
T/K	p₁/bar	Range,	Parameter	Deviation
		m₂/mol kg^-1	k_sl_(m)m/kg mol^-1	of Slope
273.15	1.049	0.01 – 0.4	0.0734	0.0071	HM (57)
298.15	0.954	0.1 – 0.6	0.0568	0.0051	HM (57)
323.15	0.865	0.02 – 0.81	0.0377	0.0028	HM (57)
348.15	0.611	0.1 – 0.9	0.0260	0.0031	HM (57)
363.15	0.305	0.1 – 0.9	0.0226	0.0024	HM (57)

100 (9) Carbon dioxide + Potassium nitrate [7757-79-1] + Water

A number of workers have studied this system. Sechenov (4) at 288.35 K, Geffcken (6) at 288.15 and 298.15 K, Markham and Kobe (18) at 273.35 , 298.15 and 313.15 K, Gerecke (35) at five degree intervals between 288.15 and 328.15 K and Yasunishi and Yoshida (42) at 298.15 and 308.15 K. The salt effect parameters.

Table 65

Table 65.

	Concentration	Salt Effect	Reference
T/K	Range, c₂/mol L^-1	Parameter
		k_scc/L mol^-1
273.35	0.0 – 0.961	0.0682	MK (18)

288.15	0.536 – 1.033	0.0527	Gf (6)
	0.0 – 2.0	0.0425	G (35)
288.35	0.0 – 2.325	0.0486	S (4)

293.15	0.0 – 2.0	0.0412	G (35)

298.15	0.536 – 1.033	0.0435	Gf (6)
	0.0 – 2.664	0.0429	MK (18)
	0.0 – 2.0	0.0389	G (35)
	0.275 – 1.768	0.0419	YY (42)

303.15	0.0 – 2.0	0.0365	G (35)

308.15	0.0 – 2.0	0.0365	G (35)
	0.275 – 1.768	0.0392	YY (42)

313.15	0.0 – 2.664	0.0372	MK (18)
	0.0 – 2.0	0.0379	G (35)

318.15	0.0 – 2.0	0.0348	G (35)
323.15	0.0 – 2.0	0.0348	G (35)
328.15	0.0 – 2.0	0.0361	G (35)

100 (10) Carbon dioxide + Sodium chloride [7647-14-5] + Potassium nitrate [7757-79-1] + Water

Yasunishi, Tsuji and Sada (43) have studied this system at 298.15 K. They report the solubility of carbon dioxide in aqueous NaC1, KNO₃, and three mixed electrolyte solutions of mole fraction ratio NaC1/KNO₃ 0.25/0.75, 0.50/0.50 and 0.75/0.25. The salt effect parameters for the five solutions are given in Table 66 on the next page.

The calculated salt effect parameters assume the two electrolytes act independently. It is probably true within the experimental error of these experiments. The values are classed tentative. See Figure 11A .

Fig. 11A

Table 41

Table 66.

Ionic Strength	Concentration	Salt Effect	Salt Effect	Difference
Ratio	Range	Parameter	Parameter	%
NaCl/KNO₃	c₂/mol L^-1	k_scc/L mol^-1	Calculated
0.00/1.00	0.288 – 1.630	0.0419	-	-
0.25/0.75	0.298 – 1.664	0.0576	0.0564	2.1
0.50/0.50	0.289 – 2.173	0.0698	0.0708	1.4
0.75/0.25	0.264 – 1.723	0.0838	0.0853	1.8
1.00/0.00	0.455 – 3.400	0.0997	-	-

Fig. 11B

100 (11) Carbon dioxide + Magnesium sulfate [7487-88-9] + Sodium chloride [7647-14-5] + Potassium nitrate [7757-79-1] + Water

The system was studied by Yasunishi, Tsuji and Sada (43) at 298.15 K. The results are in Table 67.

Table 41

Table 67.

Ionic Strength	Ionic Strength	Salt Effect	Salt Effect	Difference
Ratio	Range	Parameter	Parameter	%
MgSO₄/NaCl/KNO₃	l₂/mol L^-1	k_sl_(c)c/L mol^-1	Calculated
0.80/0.20/0.0	0 – 5.46	0.0725	0.0736	1.5
0.571/0.286/0.143	0 – 3.96	0.0667	0.0729	9.3
0.0/0.50/0.50	0 – 2.17	0.0707	0.0712	0.70

The results indicate additivity of salt effects when two salts are present, but some specific effect when three salts are present. The standard errors about the regression line are 0.0004, 0.0005 and 0.0014, respectively for the three values in the order they appear in the table above. The results are classed as tentative.

100 (12) Carbon dioxide + Potassium dihydrogen phosphate [7778-77-0] + Water

Gerecke (35) studied the system at five degree intervals between 288.15 and 333.15 K at electrolyte concentrations of 0, 0.25, 0.5 and 1 Mo1 :^-1. We did not try to calculate an ionic strength for the KH₂PO₄ electrolyte. The CO₂ solubility at 1.0 mo1 L^-1 electrolyte shows a lower solubility than expected from the behavior shown at lower electrolyte concentrations. Salt effect parameters based on the solubility at 0.0, 0.25 and 0.50 mo1 L^-1 are given below:

T/K 288.15 298.15 313.15 323.15 333.15
k_scc 0.192 0.175 0.206 0.204 0.239
Std. dev. slope 0.013 0.010 0.009 0.035 0.008

The salt effect parameter shows several unusual effects. It is larger than seen for other electrolytes. There is not indication of an acid-base interaction between the carbon dioxide and the anions present in solution. If the electrolyte is mainly K⁺ , H⁺ and HPO²₄ the salt effect parameters need be divided by 3 to put them on an ionic strength basis. The values would then be consistent with values for other electrolytes. The temperature coefficient of the salt effect parameter is doubtful until confirmed by other work.

100 (13) Carbon dioxide + Phosphoric acid [7664-38-2] + Potassium dihydrogenphosphate [7778-77-0] + Water

Van Slyke, Sendroy, Hastings and Neill (13) measured the solubility of carbon dioxide in 0.150 and 0.300 mo1 L^-1 H₃PO₄ and in mixtures of 0 to 0.300 mo1 L^-1 KH₂PO₄ and 0.015 to 0.030 ni1 L^-1 H₃PO₄ at 311.2 K. The phosphoric acid data were analyzed separately, see section 19 (1). In the mixed system the solubility was corrected assuming the phosphoric acid acted independently. The correction was 0.3 % or less. The corrected solubility was treated as if the potassium dihydrogen phosphate was present alone. The resulting salt effect parameter is k_scc = (0.151 ± 0.003) mo1 L^-1. See section 99 (25) for the treatment of the sodium salt system.

100 (14) Carbon dioxide + β-D-Fructofuranosyl-α-D-glucopyranoside (sucrose) [57-50-1] + Potassium dihydrogenphosphate [7778-77-0] + Water

de Molineri, de Cozzitorti, Sosa and Katz (51) measured the solubility of carbon dioxide in five sucrose solutions from 5 to 15 mass fraction sucrose each containing 0 to 15 mass fraction potassium dihydrogen phosphate at temperatures of 288.15, 298.15 and 308.15 K. The evaluator calculated the salt effect parameters in Table 68 (next page). The 1g L vs m₃ plots showed a small concave curvature and extrapolated to a carbon dioxide solubility in the aqueous sucrose solutions that was usually about 1 % low.

There are small, but consistent increases in the salt effect parameter with increasing temperature, and decreases in the parameter with increasing sucrose content. It is interesting to compare these results with the results of the aqueous KH₂PO₄, System 100 (12) above. The results from the aqueous sucrose solutions would represent the sucrose + water system, but no calculations were made for the system.

100 (15) Carbon dioxide + Potassium hydrogen oxalate [127-95-7] + Water

Van Slyke, Sendroy, Hastings and Neill (13) measured the solubility of carbon dioxide in 0.300 and 0.600 mo1 L^-1 KHC₂O₄ at 311.2 K. The molar salt effect parameter is k_scc = (0.0683 ± 0.0003) mo1 L^-1 and is classed tentative.

Table 20

Table 68.

	Sucrose	KH₂PO₄ Molality	Salt Effect	Std. Dev.
T/K	10²w₂	Range, m₃/mol kg^-1	Parameter	of Slope
			k_smc/kg mol^-1
288.15	5	0 – 1.378	0.1299	0.0029
298.15	5	0 – 1.378	0.1305	0.0028
308.15	5	0 – 1.378	0.1310	0.0034
288.15	7.5	0 – 1.422	0.1263	0.0034
298.15	7.5	0 – 1.422	0.1284	0.0026
308.15	7.5	0 – 1.422	0.1285	0.0033
288.15	10	0 – 1.469	0.1257	0.0027
298.15	10	0 – 1.469	0.1269	0.0026
308.15	10	0 – 1.469	0.1270	0.0034
288.15	12.5	0 – 1.520	0.1245	0.0030
298.15	12.5	0 – 1.520	0.1257	0.0026
308.15	12.5	0 – 1.520	0.1263	0.0035
288.15	15	0 – 1.575	0.1236	0.0028
298.15	15	0 – 1.575	0.1259	0.0028
308.15	15	0 – 1.575	0.1263	0.0035

100 (16) Carbon dioxide + Lactic acid [50-21-5] + Potassium lactate [996-31-6] + Water

Van Slyke, Sendroy, Hastings, and Neill (13) measured the solubility of carbon dioxide in 0.150 and 0.300 mo1 L^-1 lactic acid and in mixtures of 0.150 and 0.300 mo1 L^-1 potassium lactate and 0.100 to 0.300 mo1 L^-1 lactic acid at 311.2 K. The lactic acid alone shows a small and scattered effect (see section 99(30) and is considered to contribute negligible effect in the mixture. The data were treated as if potassium lactate alone was present. The result is k_scc = (0.0959 ± 0.0004) mo1 L^-1. The value is classed tentative.

100 (17) Carbon dioxide + Potassium thiocyanate [333-20-0] + Water

The system was studied by Sechenov (5) at 288.35 K in water and three aqueous solutions to over 10 mo1 L^-1 KSCN. The salt effect parameter, k_scc = (0.041 ± 0.03) L Mo1^-1, classed tentative.

100 (18) Carbon dioxide + Potassium aluminum sulfate [10043-67-1] + Water

Only Rosenthal (24b) reports measurements on this system, and he reports on only one dilute solution at 293.15 K. The salt effect parameter has been calculated on both a concentration and ionic strength basis. The values are k_scc = 0.84 and k_s1(c)c = 0.094. The values are classed as tentative. Ionic strength was calculated assuming 100 % dissociation into potassium, aluminum and sulfate ions.

101(1) Carbon dioxide + Robidium chloride [7791-11-9] + Water
102 (2) Carbon dioxide + Cesium chloride [7647-17-8] + Water

Geffcken (6) measured the solubility of carbon dioxide in both RbC1 and CsC1 aqueous solutions at temperatures of 288.15 and 298.15 K. Gerecke (35) measured the solubility of carbon dioxide in aqueous solutions of CsC1 at temperatures of 288.15, 293.15 and 303.15 K at concentrations up to 2 mo1 L^-1. The salt effect parameters from these data are see in Table 69.

Table 69

Table 69.

	Electrolyte	No. of	Concentration	Salt Effect	Reference
T/K		Detn.	Range	Parameter
			c₂/L mol^-1	k_scc/L mol^-1
288.15	RbCl	4	0 – 1.012	0.060	Gf (6)
298.15	RbCl	4	0 – 0.55	0.058	Gf (6)

288.15	CsCl	2	0 – 0.55	0.045	Gf (6)
		4	0 – 2	0.036	G (35)
293.15	CsCl	4	0 – 2	0.030	G (35)
298.15	CsCl	2	0 – 0.55	0.044	Gf (6)
		4	0 – 2	0.032	G (35)
303.15	CsCl	4	0 – 2	0.031	G (35)

The CsC1 salt effect parameters at 288.15 and 298.15 K from the two papers show fair agreement considering the small effect and the fact that all the Geffcken (6) measurements were made at low electrolyte concentrations. The evaluator has a slight preference for the results of Gerecke (35) except for the 293 K value that appears to be too small.

MISCELLANEOUS

The papers of Passauer (14), Nahoczky (15) and Kobe and Williams (16) contain a number of measurements in just one electrolyte solution for each system studied. A number of these have already been cited under the appropriate system. Other systems, for which these papers are the only data, are listed below.

Both Passauer (14) and Nahoczky (15) made measurements in water and in electrolyte solutions at or near saturation. They did not give an electrolyte saturation concentration, alth0ough Nahoczky (15) did give the saturated solution density. The evaluator did calculate a few salt effect parameters based on the carbon dioxide solubility in water and in the saturated salt solution using handbook values of the salt solubility. The values appear reasonable and it would seem that the data have some value. The systems not referenced earlier are listed below. However, no salt effect parameters are given because of uncertainty in the electrolyte solubility and a hesitation not to give salt effect parameters based only one salt concentration.

The work of Kobe and Williams (16) is more complete. They did not work at electrolyte saturation, and they give the salt mass % composition. Salt effect parameters were calculated using International Critical Table densities except for mixed electrolyte solutions.

Passauer (14). Solubility measured at or near salt saturation at 293 K and one atm.

33 (3) Carbon dioxide + Zinc iodide [10139-47-6] + Water
37 (1) Carbon dioxide + Silver nitrate [[7761-88-8] + Water
41 (5) Carbon dioxide + Iron (II) chloride [7758-94-3] + Water
96 (3) Carbon dioxide + Barium iodide [13718-50-8] + Water
99 (35) Carbon dioxide + Sodium nitrate [7632-00-0] + Water
99 (36) Carbon dioxide + Sodium hydrogen carbonate [144-55-8] + Water
99 (37) Carbon dioxide + Sodium dichromate [10588-01-9] + Water

Nahoczky (15). Solubility measured at or near salt saturation at 288 K and on atm. Solution densities were given.

48 (1) Carbon dioxide + Manganese sulfate [7785-87-7] + Water
52 (1) Carbon dioxide + Ammonium molybdate [12027-67-7]
93 (4) Carbon dioxide + 1/5 ethanol [64-17-5] + Magnesium sulfate [7487-88-9] + Water
99 (38) Carbon dioxide + 1/2 Magnesium chloride [7786-30-3] + 1/2 sodium chloride [7647-14-5] + Water
99 (39) Carbon dioxide + 1/2 Magnesium sulfate [7487-88-9] +1/2 Sodium chloride [7647-14-5] + Water
99 (40) Carbon dioxide + 1/3 Manganese sulfate [7785-87-7] + 1/3 Magnesium chloride [7786-30-3] +Sodium chloride [7647-14-5] + Water
99 (41) Carbon dioxide + 1/3 Manganese sulfate [7785-87-7] + 1/3 Magnesium sulfate [7487-88-9] + Sodium chloride [7647-14-5] + Water
99 (42) Carbon dioxide + 1/2 Glycerine [56-81-5] + Sodium thiosulfate [7772-98-7] + Water
99 (43) Carbon dioxide + 1/2 Magnesium sulfate [7487-88-9] + 1/2 Sodium thiosulfate [7772-98-7] + Water
100 (19) Carbon dioxide + Potassium oxalate [583-52-8] + Water
100 (20) Carbon dioxide + Potassium ferrocyanide [13746-66-2] + Water
100 (21) Carbon dioxide + Potassium dichromate [7778-50-9] + Water

Kobe and Williams (16). Solubilities measured at one stated concentration at 298.15 K and one atm pressure.

99 (44) Carbon dioxide + Sulfuric acid [7664-93-9] + Sodium chloride [7647-14-5] + Water

The aqueous solution was 5 mass % H₂SO₄ (0.680 mo1 kg^-1) and 20 mass % NaC1 (4.562 mo1 kg ^-1). The molal ionic strength salt effect parameter assuming complete dissociation of the acid is k_sl(m)c = 0.0605.

99 (45) Carbon dioxide + ortho-phosphoric acid [7664-38-2] + Trisodium phosphate [7601-54-9] + Water

The aqueous solution was 7 mass % (0.861 mo1 kg^-1) H₃PO₄ and mass % (0.735 mo1 kg ^-1) Na₃PO₄. The molal salt effect parameter is k_smc = 0.293.

99 (46) Carbon dioxide + Aerosol OT [577-11-7] + Water
99(47) Carbon dioxide + Teepol CH 53 [50642-03-0] + Water

Gjaldbaek (24a) measured the solubility of carbon dioxide in Aerosol OT, and Rosenthal (24b) in a single dilute Teepol-water mixture. The values are classed tentative as there are no other data with which to compare them.
93 (3) Carbon dioxide + Magnesium nitrate [10377-60-3] + Water

Solubility data are reported on the system by Markham and Kobe (18) at 273.35, 298.15, and 313.15 K and by Yasunishi and Yoshida (42) at 298.15 K. The salt effect parameters from the slope of 1g L vs. I₂ plots are given in Table 24 (next page). The individual values are classed as tentative, but the combined data of the two papers at 298.15 K given in [ ] in Table 24 is classed as recommended. Multiplication of the concentration range by three will give the ionic strength range.

Table 20

Table 23.

	MgSO₄ Molality	Salt Effect	Std. Dev.	Reference
T/K	Range, m₂/mol kg^-1	Parameter	of Slope
		k_sl_(m)m/kg mol^-1
273.15	0.10 – 1.00	0.0521	0.0018	HM (57)
298.15	0.1 – 1.0	0.0305	0.0068	HM (57)
323.15	0.1 – 1.00	0.0205	0.0031	HM (57)
348.15	0.1 – 2.0	0.0129	0.0009	HM (57)
363.15	0.1 – 2.0	0.0111	0.00003	HM (57)

Table 20

Table 24.

	MgSO₄ Molality	Salt Effect	Std. Dev.	Reference
T/K	Range, m₂/mol kg^-1	Parameter	of Slope
		k_sl_(m)m/kg mol^-1
273.35	0.0 – 2.70	0.0599	0.0007	MK (18)

298.15	0.0 – 2.70	0.0459	0.0003	MK (18)
	0.203 – 3.372	0.0468	0.0003	YY (42)

[298.15	0.0 – 3.37	0.0465	0.0003	MK & YY]

313.15	0.0 – 2.70	0.0415	0.0003	MK (18)

94 (1) Carbon dioxide + Calcium chloride [10043-52-4] + Water

Eight papers report the solubility of carbon dioxide in aqueous calcium chloride solution at atmospheric pressure and four papers report the solubility at pressures of 48 to over 3000 bars. The low and high-pressure values will be treated separately.

Mackenzie (3), Sechenov (5), Onda, Sada, Kobayashi, Kito and Ito (36), Yasunishi and Yoshida (42), Wolf and Krause (12), Passauer (14), Kobe and Williams (16), and Eremina, Efanov and Sorokina (53) report the atmospheric pressure experimental measurements. The Wolf and Krause data were not used because the gas was a carbon dioxide/air mixture. The Passauer data was a single point in saturated salt solution and was not used because of uncertainty in the concentration of calcium chloride in saturated solution. Eremina et al. made 11 to 12 solubility measurements over the 0 to 0.025 mo1 L^-1 CaC1₂ range. Their data show linear segments ranging in slopes from -2.2 to -3.4 which the evaluator judges to be doubtful. Measurements in such dilute solutions are difficult and subject to large error [(49) and this volume preliminary material]. The large salt effect parameters from their work are classed doubtful unless confirmed by future work. The Kobe and Williams measurements were in water and in 40 mass % CaCl₂ (5.02 mo1 L^-1). A salt effect parameter was calculated from the two solubilities. It and other values are in Table 25 (next page).

The data at 288.35/289.4 and 298.15 K are shown on a logarithm of Bunsen coefficient vs. calcium chloride ionic strength plot in Figure 4 . The data of He and Morse were included after conversion of their values to Bunsen coefficient and calcium chloride concentration ionic strength using the author's density and partial pressure data, and assuming ideal gas behavior and Henry's law. The 288.35 K line was drawn with respect to the data of Sechenov (5) and the 298.15 K line with respect to the data of Yasunishi and Yoshida (42). The curvature of the 298.15 K line at ionic strength greater than about 6 mo1 L^-1 appears to be confirmed by the points of Onda et al. (36) and Kobe and Williams (16), but not the final value of He and Morse (57). The differences in the curves at 288.35 and 298.15 K can be resolved only with further experimental work.

Mackenzie's results are classed doubtful. The salt effect parameters from his solubility values are smaller than those reported by other workers, they show more scatter about the slope and they do not show a regular change with temperature.

Sechenov's value at 288.35 K is classed tentative. Yashunishi and Yoshida's measured the solubility of carbon dioxide up to 4.53 mo1 L^-1 calcium chloride at 298.15 K. Above about 2 mo1 L^-1 calcium chloride there is a definite curvature to the 1g L vs. c₂ data. Thus, we have fitted the salt effect parameter to the near linear part of the data. The data of Onda et al. go to 2.17 mo1 L^-1 calcium chloride. Both data sets are classed tentative. The combined result given in [ ] (Table 25) uses four data points from Yasunishi and Yoshida and eight data points from Onda et al.. It is the recommended value at 298.15 K.

Yasunishi and Yoshida's data at 308.15 K and the resulting salt effect parameter are classed as tentative.

Table 20

Table 25.

	CaCl₂ Conc.	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂/mol L^-1	Parameter	of Slope
		k_sl_(c)c/L mol^-1
281	0.41 – 1.62	0.0452	0.0048	Mac (3)

288.35	0 – 4.34	0.0700	0.0013	S (5)

289.4	0.41 – 1.62	0.0449	0.0004	Mac (3)

295	0.41 – 1.62	0.0398	0.0044	Mac (3)

298.15	0.18 – 2.17	0.0616	0.0004	OSKKI (36)
	0.23 – 4.53	0.0521	0.0024	YY (42)
	0.23 – 2.0	0.0606	0.0013	YY (42)
	0.0, 5.02	0.0476	-	KW (16)
	0.0 – 0.025	1.01	0.21	EES (53)
[298.15	0.18 – 2.17	0.0626	0.0005	OSKKI & YY]

303	0.41 – 1.62	0.0433	0.0068	Mac (3)

308.15	0.30 – 2.14	0.0548	0.0009	YY (42)

313.15	0.0 – 0.025	0.724	0.154	EES (53)

Fig. 4

The data of He and Morse (57) were measured under somewhat different conditions. They report both the salt and gas in molal units. They used different carbon dioxide pressures at each temperature. The temperatures and pressures of their measurements are (temperature, K)/(pressure/bar): 273.15/0.954, 298.15/0.930, 323.15/0.843, 348.15/0.595 and 363.15/0.297. The measurements are reported for the gas solubility up to 5.0 molal CaC1₂, but better straight lines that extrapolate to the water solubility value are obtained if the 5.0 molal value is omitted. The salt effect parameters from their data are below.

Table 20

Table 26.

	CaCl₂ Molality	Salt Effect	Std. Dev.	Reference
T/K	Range, m₂/mol kg^-1	Parameter	of Slope
		k_sl_(m)m/kg mol^-1
273.15	0.10 – 4.00	0.0527	0.0018	HM (57)
298.15	0.1 – 4.0	0.0559	0.0009	HM (57)
323.15	0.1 – 2.71	0.0446	0.0025	HM (57)
348.15	0.1 – 3.0	0.0075	0.0011	HM (57)
363.15	0.1 – 3.0	0.0057	0.0003	HM (57)

There are several inconsistencies in the salt effect parameters. The 273.15 K value is suspected to be low, and the 348.15 and 363.15 K values do not seem to carry on the expected temperature dependence of the lower temperature values. The values are classed as tentative, but use with caution. The evaluator does not believe there is much change with pressure, see the pressure dependent data in Table 27.

CaCl2 Conc

	CaCl₂ Conc.	Total	Salt Effect	Std. Dev.	Reference
	Range,	Pressure	Parameter	of Slope
T/K	c₂/mol L^-1	P_t/bar	k_sl_(c)m/L mol^-1
	(m₂/mol kg^-1		or k_sl_(m)x/kg mol^-1
293.15	0 – 3.44	48	0.0532	0.0008	MS (38)

323.15	0 – 1.94	48	0.0536	0.0008	MS (38)

349	0 – 3.91(m)	48	0.0365 (m)	0.0013
		300	0.0478	0.0013
		600	0.0499	0.0015	PS (22)

363.15	0 – 2.10	48	0.0528	0.0012	MS (38)

373.15	0 – 1.98	48	0.0522	0.0034	MK (40)

374.2	0 – 3.91 (m)	48	0.0562 (m)	0.0028
		300	0.0488	0.0014
		600	0.0505	0.0019	PS (22)

393/394	0 – 3.91 (m)	48	0.0541 (m)	0.0038
		300	0.0504	0.0026
		600	0.0513	0.0036	PS (22)

423.15	0 – 2.60	48	0.0487	0.0039	MK (40)

The papers of Malinin and Savelyeva (38) and Malinin and Kurovskaya (40) report the solubility of carbon dioxide in aqueous calcium chloride at temperatures of 293.15, 323.15, 353.15, 373.15 and 423.15 K at a pressure of 47.95 bars. The calcium chloride concentration ranges from 0.0 to as high as 6.95 mo1 L^-1. All of the data sets show a definite similar curvature in the 1g m₁ vs.c₂ plots. They appear nearly linear up to about 2 mo1 L^-1 CaC1₂ and this range is used to obtain a limiting salt effect parameter. The salt effect parameters are given as k_s1(c)m values with the CaC1₂ ionic strength in mo1 L^-1 and the solubility in mo1 kg^-1. The evaluator calculated approximate molal carbon dioxide solubility at 293.15 K assuming the solution densities were the same as the aqueous CaC1₂ densities at this temperature. All of the values are classed as tentative.

Prutton and Savage (22) measured the mole fraction solubility of carbon dioxide in water and in 10.1, 20.2 and 30.2 mass percent (0, 1.01, 2.28 and 3.91 molal) CaC1₂ at temperatures of 349, 374, and 393/94 K over a pressure range of 15.2 to 703 bar. The evaluator interpolated mole fraction solubility values at pressures of 47.3, 300 and 600 bar. The slopes of 1g x₁ vs m₂ were determined by a linear regression at each of the temperatures. The negative of the slopes was converted to an ionic strength scale in molality to give k_s1(m)x/kg mo1^-1 values. The salt effect parameter at 349 K and 47.3 bar appears to be too small and is classed doubtful, the other values are classed tentative.

Plyasunova and Shmulovich (55) measured the solubility of carbon dioxide at 773 K in 10 and 20 mass % CaC1₂ at pressures of 1000, 2000 and 3000 bar. The evaluator calculated molalities of both CO₂ and CaC1₂ from the mass % data and estimated salt effect parameters from the carbon dioxide solubility at the two salt concentrations. The results are:

P_total/MPa 100 200 300
k_smmkg mo1^-1 0.291 0.056 0.024
k_s1(m)m/kg mo1^-1 0.097 0.019 0.008

The change of the salt effect parameter with pressure is much larger than at pressures below 10 MPa where little pressure dependence is noted. There are no other data to compare with these and they are classed as tentative.

All the high pressure salt effect parameters are given in the table above. The results of Malinin and coworkers and of Prutton and Savage cannot be directly compared nor can either set be compared with the atmospheric results without knowledge of the solution density. They appear to be of similar magnitude. There appears to be little effect of pressure on the salting out parameter as one increases the pressure from about 50 to over 600 bars. At 100 to 300 MPa the salt effect parameters decrease (55).

94 (2) Carbon dioxide + Ammonium nitrate [6484-52-2] + Calcium chloride [10043-52-4] + Water

Onda, Sada, Kobayashi, Kito and Ito (36,37) have measured the solubility of carbon dioxide in aqueous calcium chloride and in aqueous ammonium nitrate + calcium chloride where the salt mo1 ratio is 1 mole calcium chloride to 3 moles ammonium nitrate (ionic strength ratio 1:1) At 298.15 K and atmospheric pressure the salt effect parameter for the mixed aqueous electrolyte is k_s1(c)c = 0.0372 L mo1^-1 with a standard deviation about the slope of 0.0010 for the total ionic strength range of 1.66 - 6.33.

If the salts act independently the predicted salt effect parameter would be the average of the calcium chloride and the ammonium nitrate ionic strength salt effect parameters 0.5(0.0187) + 0.5(0.0616) + 0.0402. The fact that the calculated value is 8 % larger than the experimental value indicates the possibility of some specific interaction between the salts or salts and solvent.

94 (3) Carbon dioxide + Calcium chloride [10043-52-4] + Methanol [67-56-1] + Water

Sada, Kito and Ito (41) measured the solubility of carbon dioxide in methanol-water mixed solutions of calcium chloride at atmospheric pressure at 298.15 K. For comparison with aqueous calcium chloride solutions we used the data of Onda, Sada, Kobayashi, Kito and Ito (36). The ionic strength salt effect parameters are summarized below.

Table 20

Table 28.

	Calcium chloride	Methanol	Salt Effect	Std. Dev.
	Ionic strength	Mole	Parameter	of Slope
T/K	Range, I₂/mol L^-1	Fraction	k_sl_(c)c/L mol^-1
298.15	0.54 – 6.51	0.0	0.0616	0.0004
	0.0 – 2.10	0.280	0.0607	0.0007
	0.0 – 2.25	0.389	0.0585	0.0010
	0.0 – 2.19	0.587	0.0635	0.0017
	0.0 – 2.60	0.800	0.0669	0.0003
	0.0 – 2.89	1.000	0.0721	0.0013

The results indicate a minimum in the salting out effect someplace in the methanol mole fraction range between 0.280 and 0.587, probably near mole fraction 0.4 (see also Figure 5 following section 98 (2)). The salt effect parameters are classed as tentative.

94 (4) Carbon dioxide + Calcium nitrate [10124-37-5] + Water

Onda, Sada, Kobayashi, Kito and Ito (36) and Yashunishi and Yoshida (42) have measured the solubility of carbon dioxide in aqueous calcium nitrate solutions at 298.15 K and atmospheric pressure. Their results compare well and an ionic strength salt effect parameter from their combined data is recommended. The concentration range can be made the ionic strength range of 0.69 - 10.74 by multiplying by three.

Table 20

Table 29.

	Ca(NO₃)₂ Conc.	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂/mol L^-1	Parameter	of Slope
		k_sl_(c)c/L mol^-1
298.15	0.30 – 2.11	0.0504	0.0004	OSKKI (36)
	0.23 – 3.58	0.0503	0.0006	YY (42)
[	0.23 – 3.58	0.0504	0.0005	OSKKI & YY]

95 (1) Carbon dioxide + Stronium chloride [10476-85-4] + Water

Mackenzie (3) measured the solubility of carbon dioxide in aqueous strontium chloride at atmospheric pressure and temperatures of 281, 289.4, 295 and 303 K. His data are the only results we are aware of with this salt. Mackenzie's data often show more scatter than more modern data, however, these data are consistent for the system and are classed as tentative. Note that at 303 K there is considerable improvement in the standard deviation about the slope when the value oat 0.868 mo1 L^-1 SrC1₂ is omitted. The ionic strength salt effect parameters are in the table below. The concentration range can be converted to an ionic strength range by multiplication by three.

Table 20

Table 30.

	SrCl₂ Conc.	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂/mol L^-1	Parameter	of Slope
		k_sl_(c)c/L mol^-1
281	0.65 – 2.64	0.0750	0.0043	Mac (3)
289.4	0.65 – 2.64	0.0720	0.0007	Mac (3)
295	0.65 – 2.64	0.0667	0.0033	Mac (3)
303	0.65 – 2.64	0.0643	0.0093	Mac (3)
		0.0590^a	0.0043	Mac (3)

96 (1) Carbon dioxide + Barium chloride [10361-37-2] + Water

The solubility of carbon dioxide in aqueous barium chloride (usually dissolved as the dihydrate) at atmospheric pressure is reported by Mackenzie (3) at 281, 285.7, 288, 289.4, 295 and 303 K, by Sechenov (4) at 288.35 K, by Findlay and Shen (9) at 298.15 K, by Onda, Sada, Kobayashi, Kito and Ito (36) at 298.15 K, by Yasunishi and Yoshida (42) at 298.15 K and by Eremina, Efanov and Sorokina (53) at 298.15 and 313.15 K.

The data of Mackenzie are not consistently reliable and the measurements of Sechenov include only one barium chloride solution, thus both data sets are classed as doubtful. Eremina et al. (53) measured ten solubilities over the 0.0 to 0.050 mo1 L^-1 BaC1₂. Measurements in such dilute solutions are difficult and subject to large error [(49) and this volume preliminary material]. The salt effect parameters from their data in the table below are classed as doubtful until confirmed by future new work. The data from the other three papers are classed as tentative. The result at 298.15 K from the combined data of references (36) and (42) is the preferred tentative salt effect parameter. Results are summarized in Table 31 (next page).

96 (2) Carbon dioxide + Ammonium nitrate [6484-52-2] + Barium chloride [10361-37-2] + Water

Onda, Sada, Kobayashi, Kito and Ito (36,37) have measured the solubility of carbon dioxide in aqueous barium chloride and in six aqueous mixtures of ammonium nitrate and barium chloride in the ratio of 1 mo1 BaC1₂ to 2.60 mole NH₄NO₃ (ionic strength ratio 3.00 BaC1₂ to 2.60 NH₄NO₃). The ionic strength salt effect parameter is, k_sl(c)c = 0.0441 with a standard deviation about the slope of 0.0006 for the 0.33 to 1.69 ionic strength range at 298.15 K.

If the two salts act independently one would predict from the salt effect parameters of BaC1₂ and NH₄NO₃ a salt effect parameter of [3(0.0715) + 2.60 (0.0187)]/5.60 = 0.0470 which is 6.6 % larger than the experimental value. The result suggests the possibility of a specific interaction in the system.

Table 20

Table 31.

	BaCl₂ Conc.	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂/mol L^-1	Parameter	of Slope
		k_sl_(c)c/L mol^-1
281	0.38 – 1.54	-		Mac (3)
285.7	0.766	-		Mac (3)
288	0.1.541	-		Mac (3)

288.35	0 – 1.59	0.068		S (4)

289.4	0.38 – 0.766	-		Mac (3)

295	0.38 – 1.54	0.069	0.006	Mac (3)

298.15	0.115 – 0.408	0.0747	0.0037	FS (9)
	0.155 – 1.564	0.0703	0.0006	YY (42)
	0.371 – 1.082	0.0715	0.0030	OSKKI (36)
	0.0 – 0.050	0.124	0.045	EES (53)

[298.15	0.155 – 1.564	0.0715	0.0006	YY & OSKKI]

303	0.38 – 1.54	0.0740	0.0023	Mac (3)

313	0.0 – 0.050	0.041	0.056	EES (53)

98 (1) Carbon dioxide + Lithium chloride [7447-41-8] + Water

The solubility of carbon dioxide in aqueous lithium chloride solutions is reported in four papers. Sechenov (5) reports the solubility in seven solutions between 0 and 11.83 mo1 L^-1 LiC1 at 288.35 K and atmospheric pressure, Gerecke (35) reports the solubility in five solutions between 0 and 3.75 mo1 L^-1 LiC1 at five degree intervals between temperatures of 288.15 and 333.15 K. Onda, Sada, Kobayshi, Kito and Ito (36) report the solubility in six solutions between 0 and 5.05 mo1 L^-1 LiC1 298.15 K. Sada, Kito and Ito (41) report the solubility in four solutions between 0 and 1.18 mo1 L^-1 LiC1 at 298.15 K.

The results of Sechenov, of Onda et al. and of Sada et al. give good straight lines on 1g L vs. c₂ plots and the slopes show fair agreement. Their results are classed tentative. The data of Gerecke presents problems. At the lower temperatures the solubility of carbon dioxide is greater than in water at the concentrations of 0.43, 0.77 and 1.42 mo1 L^-1 LiC1 at the higher temperatures the solubility is greater than in water in the first two solutions. Thus, the initial salt effect is a salting in. There is no hint of any such behavior in the other three papers. If the water value is excluded from the fitted straight line the Gerecke data gives satisfactory slopes for salting out, but the salt effect parameters increases with increasing temperature, which has not been confirmed in the work of others. Note that the salt effect parameters from Gerecke's data extrapolate to a solubility in pure water that is 27 % larger than the actual solubility. Gerecke's results are classed doubtful, use with caution. Salt effect parameters are in the table below.

Table 20

Table 32.

	LiCl Concentration	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂/mol L^-1	Parameter	of Slope
		k_scc/L mol^-1
288.15	0.43 – 3.75	0.0673	0.0018	G (35)

288.35	0 – 11.38	0.0779	0.0002	S (5)

298.15	0.43 – 3.75	0.0666	0.0015	G (35)
	0 – 5.05	0.0749	0.0014	OSKKI (36)
	0 – 1.18	0.0824	0.0012	SKI (41)

308.15	0.43 – 3.75	0.0736	0.0041	G (35)
318.15	0.43 – 3.75	0.0821	0.0051	G (35)
328.15	0.43 – 3.75	0.1026	0.0031	G (35)

98 (2) Carbon dioxide + Lithium chloride [7447-41-8] + Methanol [67-56-1] + Water

Sada, Kito and Ito (41) measured the solubility of carbon dioxide in methanol-water mixed solvent at four concentrations between 0 and as much as 2.29 mo1 L^-1 LiC1 at 298.15 K. The salt effect parameters for the four mixed solvents, pure water and pure methanol are in the table below.

Table 20

Table 33.

	Lithium Chloride	Methanol	Salt Effect	Std. Dev.
	Concentration	Mole	Parameter	of Slope
T/K	Range, c₂/mol L^-1	Fraction	k_scc/L mol^-1
		x₃
298.15	0 – 1.19	0	0.0824	0.0012
	0 – 1.39	0.280	0.0992	0.0032
	0 – 1.13	0.389	0.1066	0.0019
	0 – 2.23	0.587	0.1068	0.0005
	0 – 2.29	0.800	0.1165	0.0019
	0 – 2.26	1.000	0.1243	0.0017

The salting out increases as the mole fraction of methanol increases, but it is not a regular increase, there may be a point of inflection near the 0.389 to 0.587 mole fraction methanol range. Compare the behavior here with the system where calcium chloride (Section 94 (3) ) is the electrolyte. See also Figure 5.

Fig. 5

98 (3) Carbon dioxide + Lithium bromide [7550-35-8] + Water

Gerecke (35) measured the solubility of carbon dioxide in five solutions of 0 to 1.45 mo1 L^-1 LiBr at five degree intervals at temperatures between 288.15 and 333.15 K. There are no other data on the system. The data show similarities to Gereck's results in the aqueous LiCl solutions. The solubilities at the first two concentrations (0.2 and 0.4 mo1 L^-1) are larger than in water. The value of the solubility in water fits the 1g L vs. c₂ poorly. Omitting the solubility in water value improves the fit, but the scatter is still greater than average. Several values are given in Table 34 (next page) to show trends in the data.

Table 20

Table 34.

	LiBr Concentration	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂/mol L^-1	Parameter	of Slope
		k_scc/L mol^-1
288.15	0.20 – 1.45	0.112	0.002	G (35)
298.15	0.20 – 1.45	0.121	0.011	G (35)
308.15	0.20 – 1.45	0.109	0.009	G (35)
318.15	0.20 – 1.45	0.097	0.009	G (35)

Note that the values above extrapolate to solubility in water values that are too large by 13 to 19 %. The data are classed tentative, but use with caution.

98 (4) Carbon dioxide + Lithium sulfate [10377-48-7] + Water

Lagarote (20) measured the solubility of carbon dioxide in seven solutions between 0 to 2.29 mo1 L^-1 Li₂SO₄ at 290.15 K. Gerecke (35) measured the solubility of carbon dioxide in five solutions from 0 to 2 mo1 L^-1 Li₂SO₄ at five degree intervals between temperatures of 288.15 and 333.15 K. The salt effect parameters in Table 35 have been calculated on an ionic strength basis. For the molar salt effect parameters multiply the values by 3. Agreement between the two workers is poor with the Lagarote salt effect parameter being ca. 10 % larger than the Gerecke value at either 288.15 or 298.15 K.

Table 20

Table 35.

	Li₂SO₄ Conc.	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂/mol L^-1	Parameter	of Slope
		k_sl_(c)c/L mol^-1
288.15	0 – 2.0	0.0890	0.0018	G (35)
290.15	0 – 2.29	0.1036	0.0009	L (20)
298.15	0 – 2.0	0.0936	0.0042	G (35)
308.15	0 – 2.0	0.0933	0.0083	G (35)
318.15	0 – 2.0	0.0949	0.0111	G (35)
328.15	0 – 2.0	0.0954	0.0370	G (35)

The Gerecke salt effect parameters show little change with temperature. The 1g L vs. c₂ plots reproduce the Gerecke solubility in water poorly being low by 2.5 to 10 % except the 328.15 value which is low by 18.5 %. The standard error of the slope increases at the higher temperatures. The Lagarote line reproduces the water solubility to better than 0.2 %. There is no sure way to decide between the results from the data of Lagarote and Gerecke until future work resolves the nearly 10 % difference in salt effect parameters. The evaluator has a preferance for the data of Lagarote. The Gerecke data are classed as tentative, use with caution.

99 (1) Carbon dioxide + Sodium fluoride [7681-49-4] + Water

Gerecke (35) measured the solubility of carbon dioxide in water and in 0.5 mo1 L^-1 NaF at five degree intervals between temperatures of 288.15 and 333.15 K. Salt effect parameters based on only the two experimental points are given in the table below.

Table 20

Table 36.

	NaF Concentration	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂/mol L^-1	Parameter	of Slope
		k_scc/L mol^-1
288.15	0, 0.5	0.185	-	G (35)
298.15	0, 0.5	0.230	-	G (35)
308.15	0, 0.5	0.327	-	G (35)
318.15	0, 0.5	0.400	-	G (35)
328.15	0, 0.5	0.471	-	G (35)

The results show a strong salting out and a large positive coefficient of temperature. Both properties are unusual for a 1-1 electrolyte. The evaluator knows of no other system showing this behavior. The results are classed as tentative. but use the extreme caution until confirmed by other workers.

99 (2) Carbon dioxide + Sodium chloride [7647-14-5] + Water

The papers on the solubility of carbon dioxide in aqueous sodium chloride are divided into three parts. I) Measurements at or near atmospheric pressure in which both NaCl and CO₂ are reported in mo1 L^-1 or other volume units, ii) measurements at or near atmospheric pressure in which both NaCl and CO₂ are reported in mo1 kg^-1 or other mass units, and iii) measurements at high pressures regardless of the units used for NaCl and CO₂.

i) Mackenzie (3) measured the solubility of carbon dioxide in four solutions between 1.23 and 4.86 mo1 L^-1 NaCl at temperatures of 281, 288 and 295 K; Sechenov (4, 5) measured the solubility of carbon dioxide in ten solutions between 0 and 5.40 mo1 L^-1 NaCl at 288.35 K; Nahoczky (15) and Passauer (14) measured the solubility of carbon dioxide in water and in saturated NaCl solution at 288/293 K; Kobe and Williams (16) measured the solubility of carbon dioxide in four solutions between 0 and 5.07 mo1 L^-1 at 298.15 K; Rosenthal (24b) measured the solubility of carbon dioxide in four solutions between 0 and 5.06 mo1 L^-1 NaCl at 293.15 K; Yeh and Peterson (31) measured the solubility in two solutions at 0 and 0.155 mo1 L^-1 NaCl at four temperatures between 298.15 and 318.15 K; Gerecke (35) measured the solubility of carbon dioxide in five solutions between 0 and 4.3 mo1 L^-1 at five degree intervals between 288.15 and 333.15 K; Onda, Sada, Kobayashi, Kito and Ito (36) measured the solubility of carbon dioxide in nine solutions between 0 and 3.01 mo1 L^-1 NaCl at 298.15 K; Yasunishi and Yoshida (42) measured the solubility of carbon dioxide in eight or more solutions between about 0.45 and up to 5.10 mo1 L^-1 NaCl at temperatures of 288.15, 298.15 and 308.15 K; and Burmakina, Efanov and Shnet (45) measured the solubility of carbon dioxide at 298.15 K in nine solutions between 0 and 0.200 mo1 L^-1 NaCl. Vazquez, Chenlo and Pereira (61) measured the solubility of carbon dioxide at 298.15 K and 0.1013 MPa in five solutions between 0 and 2.738 mo1 L^-1 NaCl. Vazquez, Chenlo, Pereira and Peaguda (64) measured the solubility of carbon dioxide at 5 degree intervals from 293.1 to 308.1 K and 0.1013 MPa in four solutions from 0.684 to 2.738 mo1 L^-1 NaCl. Wolf and Krause (12) made seven measurements up to saturated NaCl at 293 K. Their data were not used because the gas was a carbon dioxide/air mixture.

Table 20

Table 37.

	NaCl Concentration	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂/mol L^-1	Parameter	of Slope
		k_scc/L mol^-1
279.6	1.23 – 4.86	0.1004	0.0092	Mac (3)

288.15	1.23 – 4.86	0.0971	0.0057	Mac (3)
	0 – 4.3	0.0858	0.063	G (35)
	0.48 – 4.72	0.1010	0.0011	YY (42)
	0, 5.45 (est)	0.0840	-	N (15)
288.35	0 – 5.4	0.1038	0.0012	S (4, 5)

293.15	0 – 5.06	0.1022	0.0020	R (24b)
	0 – 4.3	0.0912	0.036	G (35)
	0.68 – 2.74	0.0961	0.0023	VCPP (64)

295.15	1.23 – 4.86	0.0897	0.0029	Mac (3)

298.15	0 – 5.07	0.1000	0.0013	KW (16)
	0 – 4.3	0.0889	0.0024	G (35)
	0 – 3.01	0.1005	0.0011	OSKKI (36)
	0.46 – 5.10	0.0979	0.0007	YY (42)
	0 – 0.200	0.116	0.017	BES (45)
	0 – 2.74	0.0998	0.0008	VCP (61)
	0.68 – 2.74	0.1013	0.0013	VCPP (64)
[298.15	0 – 5.10	0.0995	0.0007	(16)(36)(42)(61)]

303.15	0 – 4.3	0.0851	0.0030	G (35)
	0.68 – 2.74	0.0871	0.0043	VCPP (64)

308.15	0 – 4.3	0.0859	0.0035	G (35)
	0.45 – 4.86	0.0931	0.0004	YY (42)
	0.68 – 2.74	0.0926	0.0027	VCPP (64)

313.15	0 – 4.3	0.0836	0.0063	G (35)
318.15	0 – 4.3	0.0798	0.0075	G (35)
323.15	0 – 4.3	0.0782	0.0078	G (35)
328.15	0 – 4.3	0.0833	0.0122	G (35)
333.15	0 – 4.3	0.0814	0.0110	G (35)

The value of 0.0995 L mo1^-1 at 298.15 K from the combined data of Kobe and Williams (16), Onda et al(36), Yasunishi and Yoshida (42), and Vazquez et al. (61) is the only recommended value in Table 37. All of the other data in Table 37 are classed as tentative, but the evaluator prefers the data of Yasunishi and Yoshida as a consistent set of data to a 20 degree temperature interval. The data of Vazquez et al. (61, 64) arrived too late to process with the other data . Their data appear to agree well with the earlier data for this system.

The mass percent data of Kobe and Williams (16) were converted to mo1 L^-1 NaCl using density data from the International Critical Tables. The solubility of NaCl at 288.15 was estimated to be 6.20 mo1 kg^-1 or 5.45 mo1 L^-1 in the calculation from the data of Nahoczky (15).

In addition to the data in Table 37, salt effect parameters were calculated form the data of Yeh and Peterson (31). They report solubilities for water and for 0.9 mass % NaCl which the evaluator calculated to be 0.155 mo1 L^-1 NaCl. The salt effect parameters from the two measurements ranged from 0.199 to 0.186 which is about two times the magnitude of the salt effect parameter values in Table 37. We have no confirming evidence this is a real effect in dilute solutions, so we class the result doubtful unless confirmed by future work. Burmakina et al. (45) made nine measurements in the 0-0.200 mo1 L^-1 NaCl range. Measurements in the very dilute solutions are difficult and subject to large error [(49) and this volume introductory material]. They did obtain a somewhat larger salt effect parameter with a relatively large standard error of the slope. This may be an important observation, but until it is confirmed by other workers it also is classified as doubtful.

Figure 6 shows logarithm of Ostwald coefficient vs. sodium chloride concentration (ionic strength) at 288.15 and 298.15 K. The experimental values come from papers published over the last 117 years and show a linear relationship to over 5 mo1 L^-1 sodium chloride. The data of He and Morse (57) were converted from molal to volume units assuming ideal gas behavior and Henry's law using density and partial pressure data from their paper. Their results show considerable scatter. This is not surprising in that they made the 298.15 K measurements at a carbon dioxide partial pressure of 0.039 atm and reported the measured solubility to only two significant figures.

Fig. 6

ii) The data of He and Morse (57) are reported in molality for both NaCl and CO₂. They measured the solubility of carbon dioxide in five to seven solutions between 0.1 or 0.5 to 6.14 mo1 kg^-1 NaCl at five temperatures between 273.15 and 363.15 K and carbon dioxide partial pressure between 0.0395 and 0.979 bar (a different pressure at each temperature, see Table 38 next page). The salt effect parameters are in Table 38.

Table 38

Table 38.

		NaCl Molality	Salt Effect	Std. Dev.	Reference
T/K	p₁/bar	Range	Parameter	of Scope
		m₂/mol kg^-1	k_smm/kg mol^-1
273.15	0.979	0.0 – 6.0	0.0835	0.0017	HM (57)
298.15	0.0395	0.5 – 6.14	0.0853	0.0029	HM (57)
323.15	0.865	0.5 – 6.14	0.0598	0.0032	HM (57)
348.15	0.611	0.1 – 6.0	0.0204	0.0008	HM (57)
363.15	0.305	0.1 – 6.0	0.0195	0.0010	HM (57)

The salt effect parameters from the data of He and Morse are classed as tentative, but there are several concerns about the results. It is unlikely that the 273.15 K value is smaller than the 298.15 K value. The sharp decrease in salt effect parameter magnitude between 323.15 and 363.15 K needs confirmation. There are nonelectrolyte and salt solutions that show a change from salting out to salting in at about this temperature range, but we have seen no indication of this behavior for carbon dioxide and any salt in this review.

iii) There are several papers that report the solubility of carbon dioxide in aqueous NaCl solution at elevated temperatures and pressures. Ellis and Golding (30) measured the solubility of carbon dioxide in four solutions between 0 and 2.0 mo1 L^-1 NaCl at temperatures between 445 and 607 K and partial pressures between 1.59 and 9.31 MPa CO₂; Takenouchi and Kennedy (32) measured the solubility of carbon dioxide at 0, 1.09 and 4.28 mo1 kg^-1 NaCl at 50 degree intervals between 423.15 and 723.15 K and total pressures between 10.0 and 140.0 MPa; Malinin and Savelyeva (38) measured the solubility of carbon dioxide in up to seven solutions of 0 to 4.46 mo1 L^-1 NaCl at temperatures of 298.15, 323.15, and 358.15 K and a total pressure of 4.795 MPa; Malinin and Kurovskaya (40) measured the solubility of carbon dioxide in up to seven solutions between 0 and 5.92 mo1 L^-1 NaCl at temperatures of 298.15, 373.15 and 423.15 K and total pressure of 4.80 MPa; Cramer (46) measured the solubility of carbon dioxide in 0, 0.49 and 1.86 mo1 L^-1 NaCl at temperatures between 298.15 and 511.8 K and pressures between 0.8 and 6.2 MPa; and Nighswander, Kalogerakis, and Mehrotra (52) measured the solubility of carbon dioxide in water and in 1 weight percent (0.173 mo1 kg^-1) NaCl at temperatures of about 353.65, 393.15, 433 and 470 K and pressures between about 2.1 and 10.2 MPa. Rumpf, Nicolaisen, Öcal and Maurer (59) measured the solubility of carbon dioxide in 4 and 6 mo1 kg^-1 NaCl between 313 and 433 K and up to 10 MPa total pressure. There is also a 1981 Ph.D. Thesis of Drummond (44) that contains additional data.

All of the papers above contain useful information on the solubility of carbon dioxide as a function of temperature and pressure. However, not all of the experimental studies above are suitable for the evaluation of the effect of electrolyte ionic strength (salt effect parameter) on the carbon dioxide solubility. The paper of Nighswander, Kalogerakis and Mehrotra (52) reports carbon dioxide solubility in water and one mass percent (0.173 mo1 kg^-1) NaCl. The two solubility values over such a small molality range do not lead to reliable salt effect parameters and the paper was not used further. The paper of Takenouchi and Kennedy (32) presented problems. The evaluator converted mass percent data to molality values and made estimates of the salt effect problems. The evaluator converted mass percent data to molality values and made estimates of the salt effect parameter, k_smm/kg mo1^-1 at 423, 523 and 623 K. The salt effect parameters ranged from 0.023 to 0.26 and showed a high scatter. The data were not treated further. We agree with Dr. R. Crovetto (private communication) who questioned the data treatment in the Drummond (44) thesis for the solubility of carbon dioxide in water because no equation of state could be used with the data as presented.

The evaluator has made calculations from graphically smoothed from Ellis and Golding (30) and of Cramer (46) under several conditions of temperature and pressure. The salt effect parameters obtained are of larger magnitude and show more scatter about the regression line than other values. From Ellis and Golding at 450 K and 1.59 MPa k_scm/L mo1^-1 = 0.105 ± 0.005, at 500 K and 4.5 MPa 0.091 ± 0.011, at 540 K and 6.5 MPa 0.128 ± 0.021 and at 580 K and 6.5 MPa 0.153 ± 0.028. From Cramer (46) at 300 K and 1.0 MPa k_scx/L mo1^-1 = 0.115 ± 0.037, at 420 K and 2.0 MPa 0.135 and at 500 K and 6 MPa 0.145.

The most self-consistent high temperature and pressure carbon dioxide solubility data appear to be the data of Malinin and Savelyeva (38) and of Malinin and Kurovskaya (40). Most of the plots of lg m₁ vs. c₂ showed a slight concave curvature. A straight line through the data extrapolates to a carbon dioxide solubility in water that is too small by 2.5 to 5.0 % when the full NaCl concentration range of 0 to > 5.0 mo1 L^-1 is used. When the NaCl concentration range is 0 to about 2.0 the line extrapolates satisfactorily to the carbon dioxide solubility in water. Salt effect parameters from several NaCl concentration ranges from the Malinin et al. data at 47.95 and 48.0 MPa are in Table 39.

Table 20

Table 39.

	NaCl Conc.	Salt Effect	Std. Dev.	Reference
T/K	Range, c₂/mol L^-1	Parameter	of Slope
		k_scm/L mol^-1
298.15	0 – 2.60	0.0918	0.0011	MS (38)
	0 – 5.04	0.0808	0.0034	MK (40)
	0 – 2.1	0.0922	0.0012	(38 & 40)
	4.04, 5.04	0.0697		MK (40)

323.15	0 – 2.74	0.0791	0.0026	MS (38)
	0 – 1.79	0.0845	0.0019	MS (38)

358.15	0 – 4.46	0.0691	0.0026	MS (38)
	0 – 2.2	0.0780	0.0032	MS (38)

373.15	0 – 5.92	0.0616	0.0032	MK (40)
	0 – 2.0	0.0814	0.0031	MK (40)
	3.98 – 5.92	0.0477		MK (40)

423.15	0 – 5.65	0.0622	0.0042	MK (40)
	0 – 2.52	0.0743	0.0043	MK (40)
	2.52, 5.65	0.054		MK (40)

The evaluator prefers the values from treatment of the 0 - 2 mo1 L^-1 NaCl range. There are inconsistencies in the data at the 373 and 423 K temperatures that require further study.

The data of Rumpf et al. (59) was treated graphically to obtain smoothed solubility values at 2, 5 and 8 MPa total pressure. The solubility values in 4 and 6 mo1 kg^-1 were used to calculate a k_smm salt effect parameter. The results based on just the two solubility values are in Table 40.

Table 40

Table 40.

T/K	k_smm/kg mol^-1
	at 2 MPa	at 5 MPa	at 8 MPa
313	0.052	0.059	-
353	0.055	0.047	0.046
393	0.031	0.046	0.037
433	0.035	0.034	0.037

The Malinin and Kurovskaya values at the high concentrations of NaCl can be compared with the Rumpf et al. values remembering that k_scm + 1.15 k_smm. The values are of similar magnitude, which gives increased confidence in the reliability of the two sets of data.

99 (3) Carbon dioxide + Hydrochloric acid [7647-01-0] + Sodium chloride [7647-14-5] + Water

Van Slyke, Sendroy , Hastings and Neill (13) measured the solubility of carbon dioxide in solutions of 0.01 mo1 L^-1 HC1 and 0, 0.150 and 0.300 mo1 L^-1 NaCl at 311.2 K. The effect of the HC1 was considered negligible and the system treated as if only NaCl were present. The NaCl salt effect parameter is k_scc = (0.0931 ± 0.0036) L mo1^-1 which agrees well with the value from Yasunishi and Yoshida (42) at 308.15 K. The result is classed tentative. Kobe and Williams (16) made measurements in water and in a mixture which was 2 mass % HC1 (0.703 mo1 kg^-1) and 20 mass % NaCl (4.388 mo1 kg^-1) at 298.15 K. The ionic strength salt effect parameters in molality units are 0.0725. It is classed tentative.

99 (4) Carbon dioxide + Nitric acid [7697-37-2] + Sodium chloride [7647-14-5] + Water

Onda, Sada, Kobayashi, Kito and Ito (37) measured the solubility of carbon dioxide in aqueous mixed electrolyte of ionic strength ratio NaCl/HnO₃ 0.3988/0.6012 and 0.6458/0.3542 at 298.15 K. Plots of lg L vs I_total were reasonably linear (std error about slope of 0.0014 for both mixtures). The ionic strength salt effect parameters are in Table 41.

Table 41

Table 41.

Ionic Strength	Ionic Strength	Salt Effect	Salt Effect	Difference
Ratio	Range	Parameter,^a	Parameter,
NaCl/HNO₃	l_tot/mol L^-1	k_sl_(c)c/L mol^-1	Calculated
0.40/0.60	0, 1.40, 2.95	0.0289	0.0399	38 %
0.65/0.35	0 – 2.16	0.0587	0.0644	9.7 %

The calculated values use the salt effect parameters of 0.0004 for HNO₃ and 0.995 for NaCl. The difference indicates some specific interaction or solution structural change. The effect is definitely not additive. See Figure 11B following section 100 (10).

Experimental Data:   (Notes on the Nomenclature)

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View Figure 11 for this Evaluation

View Figure 11 for this Evaluation

References: (Click a link to see its experimental data associated with the reference)

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