A method was developed to determine the concentrations of the ionic species present in the CO2−NH3−H2O system. The 13C NMR spectra of these solutions contain two peaks, one for the carbamate and one for the carbonate and bicarbonate. The method uses the area ratio and the position of the latter peak to determine concentrations. Ion concentrations were determined at 17 different concentrations for total NH3 and CO2 and at two different temperatures, 25 and 35 °C. All measurements were for solutions in which the total concentration of NH3 was greater than that of CO2. A comparison of three different thermodynamic models showed that although the models overpredicted the amount of carbonate, all were in reasonable agreement with experiment when the total ammonia concentration was less than 3 mol/L of solvent. At the higher concentrations, all the models badly underpredicted the amount of carbamate formed and overpredicted the amount of carbonate.

202 investigathm, 0.1029 f 0.0007 V. Fvthennore, the newer set of emf data of Merken et ai. (7) leads to a value of 0.103 19 f 0.00005 V. One may conclude that the discrepancy resides in the experimental measurements, rather than, as postulated by M e n et al. ( 7 7), in the failure of Sadek et ai. to ailow for ion pairing and their use of too low a value for the dielectric constant.As expected, the transfer properties given in Table V I reflect the decreasing stabillzation of HCI as water is replaced by the organic solvent. An increase of pK, as 2-methoxyethanol is added to the water solvent is evident in Table V I I . Here, changes in the lon-solvent interaction pattern are presumably reinforced by enhanced ion-ion interaction favored by the decreasing dielectric constant of the medium. , , 777877-0; N a w , , 7 5 5 8 7 9 4 2-methoxyethanol, 109-86-4. Llterature Cited R.gbtV NO. A@, 7783-90-6 Ag, 7440-22-4; HCI, 7647-01-0; H,, (1) Taylor, M. J.; Walter, C. A.; Elford, B. C. cryobidogy 1978, 75, 452. (2) Taylor, M. J.; Plgnat, Y. Cryobbbgy 1982, 79, 99. (3) vega, 407. c. A.; ~osado, E.; Bates, R. G. J . chem. EW. mta ieeo. 35, (4) vwa, c. A.; ~elgedo, s. J . chem. ~n g . m d p iew, 37,74. (5) Thun. H. P.; S t a~k . B. R.; Bates, R. G. J . Res. Net/. &. Stand.. Sect. A . 1970, 7 4 , 641. (6) Sadek, H.; Tadros, T. F.; ECHarakany, A. A. Ek?ctrochbn. Acta 1971, 76. 339. .. . . . (7) Merken, G. V.; Thun. H. P.; Verbeek, F. Bull. Soc. CNm. 19&. 1977, 86, 649. (6) Shanbhag. P. M.; Vega, C. A.; Bates, R. 0. BUN. Soc. Chim. Be&. 1981. 90, 1. (9) Simon, W.; MGrikofer, A.; HeilbronmK, E. Helv. Sesta, B.; Battistlni, M.; Petrucci, S. J . Am. O m . Soc. 1972, 94, 2961. (12) Vega, C. A.; Rosado, E.; Bates, R. G. J. chem. -. , in press. (13) Merken, G. V.; Thun, H. P.; Verbeek, F. €/ectfochitn. Acta 1974, 19, 947. (14) Merken, G. V.; Thun, H. P.; Verbeek. F. E k f " . Acta 1976, 27, 11. (15) Klein, S. D.; Bates, R. G. BUH.New prowre-tempwature-overaH compodtlon vapor-lk@d equlllbrlum (VLE) data are reported for the ammonla-water system at five temperatures between 20 and 140 O C and up to 500 pda. Them data have been converted to f -P -x data, and vapor-phase composltlons have been calculated by means of a Redlich-Kwong equatlon of state modified to Include Peneloux's volume translation and a dendty-dependent mlxlng rule. I n order to achieve agreement of calculated vapor-phase compor#knr wlth previous literature results, lt was necessary to use Merent k4 values In the vapor and Hqukl phases. IntroductlonThere have been a number of experimental ( 7-9) and computational ( 7 , 70-74) efforts to characterize the vapor-liquid equHibriwn (VU) behavior of the NH, -H, O system. Gillespie et ai. (7) poht out that, prior to their work, there was disagreement between experimental and calculated vapor-phase compositions, especially at high ammonia concentrations. Some authors had attributed these discrepancies to thermodynamically inconsistent data (Edwards et al. (74), for example), others to shortcomings in existing models (Peng and Ro...

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