Aqueous solutions of the mono- and di-hydrogenphosphate salts of sodium and potassium at elevated temperatures. Isopiestic results

✍ Scribed by H.F. Holmes; J.M. Simonson; R.E. Mesmer

• Publisher: Elsevier Science
• Year: 2000
• Tongue: English
• Weight: 323 KB
• Volume: 32
• Category: Article
• ISSN: 0021-9614
• DOI: 10.1006/jcht.1999.0571

✦ Synopsis

Isopiestic molalities of aqueous solutions of Na 2 HPO 4 , K 2 HPO 4 , NaH 2 PO 4 , and KH 2 PO 4 have been measured at intervals from T = 383.15 K to T = 498.15 K, with NaCl (aq) as the isopiestic standard for the calculation of osmotic coefficients. Osmotic coefficients for these electrolytes, already low at T = 298.15 K, decreased even more at elevated temperatures, becoming quite low with equilibrium isopiestic molalities as large as 15 mol • kg -1 . Minor modifications of the standard ion-interaction model were necessary in order to obtain an acceptable fit of the experimental osmotic coefficients. Stoichiometric activity coefficients were computed from parameters resulting from the least-squares fit, which was quite good, of the osmotic coefficients. In the case of the di-hydrogenphosphates the relative order of the osmotic and activity coefficients reversed at the higher temperatures, which was not observed for the mono-hydrogenphosphates.