Densities and Apparent Molar Volumes of Na₂SO₄(aq) and K₂SO₄(aq) at Temperatures from 298 K to 573 K and at Pressures up to 30 MPa

Abstract

Densities of Na2SO4(aq) and K2SO4(aq) have been measured by vibrating-tube densitometry at concentrations of 0.01 mol·kg-1 to 1.0 and 0.5 mol·kg-1, respectively, and at temperatures from 298.15 K to 572.7 K and pressures up to 30.7 MPa. Apparent molar volumes derived from these data were extrapolated using the Pitzer ion-interaction model to yield partial molar volumes of these electrolytes at infinite dilution. The two salts show similar behaviors over the whole range of conditions studied.

Volumes of MgCl2(aq) at temperatures from 298 K to 623 K and pressures up to 30 MPa

“…When necessary, 0 was used as a placeholder and 1 put in parenthesis after the number (for example for V f,m = −1020(1) cm 3 ·mol −1 the error is 2Q300 cm 3 ·mol −1 ). As has been found in previous densimetric studies of this kind with other electrolytes, (21,(27)(28)(29) molar volumes derived for low molalities (m E 0.1 mol·kg −1 ) occasionally exhibit large positive deviations from the bulk of the data. This is almost certainly due to insufficient degassing and, consequently, such points were discarded.…”

“…(22) The uncertainties in both Dr and V f,m depend strongly on molality, temperature, and, to a lesser extent, on pressure, as discussed elsewhere. (21) As before, (26) the reliability of Dr and V f,m is indicated by printing a digit only if its absolute error was estimated to be less than 30. When necessary, 0 was used as a placeholder and 1 put in parenthesis after the number (for example for V f,m = −1020(1) cm 3 ·mol −1 the error is 2Q300 cm 3 ·mol −1 ).…”

“…We do not have any explanation for this except that the earlier measurements were performed immediately before the tube was pierced due to corrosion and the instrument was probably not functioning correctly. Only the later set of measurements which is reasonably consistent with the data on sulphates at the same temperature (21) is included here.…”

“…(20) The present measurements on MgCl 2 (aq) were performed simultaneously with those recently reported for Na 2 SO 4 (aq) and K 2 SO 4 (aq). (21) The interested reader should consult the above two papers for more detailed information on instrument and procedure as only the more salient features are included here. Measurements of the vibration period t of the solutions were alternated throughout with those for pure water t o to monitor the stability of the densimeter baseline.…”

“…As the densities of MgCl 2 (aq) solutions were obtained over a 2 year period, the calibration constants for two different vibrating tubes (21) constructed of Hastelloy-C and, later, (platinum + 0.2 mass fraction of rhodium), are given in table 1. As a check on the accuracy of the results, measurements were routinely performed on a 3 mol·kg −1 NaCl solution and compared with recommended literature values.…”