The activity and osmotic coefficients of aqueous sodium bicarbonate solutions

Abstract

We have used the isopiestic technique to measure the osmotic coefficients of mixed aqueous solutions of NaHCO 3 and Na 2CO 3 at 298.15 K. During the isopiestic equilibration, the systems were pressurized with CO 2(g) to reduce the loss of CO 2 from the initially pure NaHCO 3 solutions and the consequent conversion of bicarbonate to carbonate. Following equilibration, a differential titration analysis was performed to determine the amounts of carbonate and bicarbonate in the solutions. We have calculated the osmotic and the activity coefficients of pure sodium bicarbonate solutions up to a molality of 1.3 mol · kg −1, using the experimentally determined osmotic coefficients for the mixtures, the osmotic coefficients for pure sodium carbonate solutions, and the equations of Reilly, Wood, and Robinson together with the assumption that the interaction coefficients are zero.