Thermodynamics of ionic-association in aqueous solutions of Ca and Mg organic salts using ion-selective electrode technique—I. Formates, acetates, propionates and butyrates

✍ Scribed by Mostafa M. Emara; Nazik A. Farid; Ahmed Wasfi

• Publisher: Elsevier Science
• Year: 1981
• Tongue: English
• Weight: 361 KB
• Volume: 26
• Category: Article
• ISSN: 0013-4686
• DOI: 10.1016/0013-4686(81)85153-5

✦ Synopsis

A&race-The divalent selective electrode together with high precision solid state, digital pH -mv -meter makes broader application of potentiometry in physical and inorganic chemistry a certainty. The above setup is used to determine the stoichiometric constants, K, for Ca and Mg ions association with formates, acetates, propionates and butymtes at 25", 35" and 45'C in aqueous media. The K-values were converted to infinite dilution X, values were found 10 be 8.4 LM-', 10.4 LM-', 19.1 LM-' and f9.3 LM-' for calcium salts of formate, acetate, propionate and butyrate respectively. Also K, values for Mg salts of formate, acetate, propionate and butyrate were found to be 7.8 LM-', 9.5 LM-', 13.1 LM-' and 13.1 LM-' respectively. Other thermodynamic parameters such as AG", AH" and AS" are also obtained from the variation of K, with temperature for each salt. The data are interpreted relative to each other on basis of pK, of the corresponding organic acid. Their temperature behaviour is similar to those salts derived from strong acids such as sulphates, rather than weak acids.