Apparent Molal Volumes and Heat Capacities of some Sulfates and Carbonates in Water at 25 °C

Abstract

The densities and volumetric specific heats of Na 2 SO 4 , K 2 SO 4 , MgSO 4 , Na 2 CO 3 , NaHCO 3 , and NaOH were measured up to an ionic strength of 1 in water at 25 °C with a flow densimeter and a flow microcalorimeter. From these data, the heat capacity for the formation of the ion pair MgSO 4 0 was evaluated as 84.9 J K −1 mol −1 . There is an anomalous increase in the apparent molal heat capacities of Na 2 CO 3 at low concentration but the apparent molal volumes are normal. This anomaly can be suppressed with NaOH. Attempts to account quantitatively for this behavior by an hydrolysis correction were not successful.