Apparent molar heat capacities of aqueous solutions of LiBO2, NaBO2, KBO2, Na2B4O7 and K2B4O7 at T = (298.12, 313.13 and 328.14) K using a Picker flow calorimeter

The apparent molar heat capacities of LiBO 2 (aq), NaBO 2 (aq), KBO 2 (aq), Na 2 B 4 O 7 (aq) and K 2 B 4 O 7 (aq) solutions at molalities from 0.01 to 2.6 mol·kg −1 , and at temperatures T  = (298.12, 313.13 and 328.14) K have been determined using a Picker flow calorimeter built in this work. Further, the standard heat capacities of these solutes were derived from the experimental data by extrapolation to infinite dilution using the Pitzer ion-interaction model. The group contribution method is used to calculate the standard molar heat capacities of tetraborate ion in three equilibria for different assumptions, among which the prediction on the assumption that the standard molar heat capacity of reaction for the association reaction is zero is the most reasonable, and the results are in good agreement with the experimental data.