Traceable mean activity coefficients of barium chloride in dilute aqueous solutions from T = (273 to 333) K and at T = 298.15 K up to the saturated solution where the molality is 1.7884 mol · kg−1

• This work reports new equations for thermodynamic quantities in BaCl2(aq).
• The form of the equations is the same as that obtained previously for salt solutions.
• The new activity and osmotic coefficients are fully traceable and transparent.
• These new values were tested thoroughly with existing literature data.

Two new Hückel equations have been determined for the activity coefficients (γ) of BaCl2 in aqueous solutions at T = 298.15 K. One of these equations is a two-parameter equation with parameters B (related closely to the ion-size parameter in the Debye–Hückel theory) and b1 (the coefficient of the linear correction term in Hückel equation where ln(γ) is presented vs. the molality). It can be used up to an ionic strength (= Im) of 2.0 mol ⋅ kg−1. The other is a three-parameter Hückel equation with parameters B, b1, and b2 (the coefficient of the quadratic correction term in extended Hückel equation), and it applies up to the saturated solution where Im is 5.3652 mol ⋅ kg−1. The two BaCl2 parameters for dilute solutions were evaluated from the isopiestic data of Robinson (1940) [4]. These new parameters were tested with all isopiestic and galvanic cell data available in the literature for this investigation. The electrochemical data measured by Tippetts and Newton using two-phase barium amalgam cells (Tippetts and Newton, 1934) [16] show that the new parameter values apply without any changes in the best case up to Im of 3.0 mol ⋅ kg−1 at temperatures from (273 to 333) K. For more concentrated solutions at T = 298.15 K, new values of b1 and b2 for the extended Hückel equation were obtained from all points up to the saturated solution in the isopiestic set of Robinson (1945) [21]. The tests of the new parameter values were carried out with the existing electrochemical, vapor pressure, isopiestic, and solubility data available for these stronger BaCl2 solutions together with the existing values for the thermodynamic properties of this salt and its hydrates. Reliable activity and osmotic coefficients for BaCl2 solutions can be solved by using the new Hückel and extended Hückel equations. The values from these equations are tabulated here at rounded molalities and they were compared to the literature values.