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Isopiestic Determination of the Osmotic and Activity Coefficients of the {yNaH2PO4 + (1 − y)KH2PO4}(aq) System at T = 298.15 K

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Abstract

Isopiestic measurements have been made for aqueous mixtures of NaH2PO4 and KH2PO4 at T = (298.15 ± 0.01) K, at NaH2PO4 ionic strength fractions y = (0, 0.19108, 0.38306, 0.58192, and 1), assuming that both electrolytes dissociate as 1:1 electrolytes, using KCl(aq) as the reference standard solution. Model parameters for an extended form of Pitzer’s ion-interaction model and also for the Clegg–Pitzer–Brimblecombe equations based on the mole-fraction-composition scale were evaluated at T = 298.15 K for NaH2PO4(aq) using the present isopiestic results (13 values), as were those for KH2PO4(aq) using the present isopiestic results (12 values), together with numerous critically-assessed osmotic coefficients for both electrolytes taken from the published literature. The thermodynamic models for KH2PO4(aq) extend to m = 2.187 mol·kg−1, which is slightly above saturation, while those for NaH2PO4(aq) extend to m = 7.5 mol·kg−1, which is below saturation. The 39 osmotic coefficients for the ternary mixtures from the present study along with 42 values from a published study were likewise represented with these models, with both the usual Pitzer mixing terms and also Scatchard’s neutral-electrolyte model mixing terms being used for the extended ion-interaction model. Two mixing parameters were needed for each of the models, and all three models gave similar quality representations of the experimental results. Maximum differences in calculated values of mean molality-based activity coefficients for these three models are ∆γ±(NaH2PO4) ≤ 0.0080 and ∆γ±(KH2PO4) ≤ 0.0043. The experimental results were also found to nearly conform to Zdanovskii’s rule.

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Acknowledgements

This work was supported by the Ministry for Science and Environmental Protection of the Republic of Serbia under Project No. 172063.

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Authors and Affiliations

  1. Institute for Multidisciplinary Research, University of Belgrade, Kneza Višeslava 1, 11 030, Belgrade, Serbia

    Tijana Ivanović

  2. Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11 001, Belgrade, Serbia

    Daniela Ž. Popović, Jelena Miladinović & Katarina Trivunac

  3. Livermore, CA, USA

    Joseph A. Rard

  4. Institute of General and Physical Chemistry, Studentski trg 12-16, 11 000, Belgrade, Serbia

    Zoran P. Miladinović

  5. Faculty of Technical Sciences, University of Priština, Kneza Miloša 7, Kosovska Mitrovica, Serbia

    Svetlana Belošević

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  1. Tijana Ivanović
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Appendix: Additional Tables Giving the Combined Uncertainties for the Individual Molalities and the Osmotic Coefficients that Include the Contributions from Uncertainties in the Standardized Molalities of the Stock Solutions

Appendix: Additional Tables Giving the Combined Uncertainties for the Individual Molalities and the Osmotic Coefficients that Include the Contributions from Uncertainties in the Standardized Molalities of the Stock Solutions

See Table 10, 11, 12, and 13.

Table 10 Experimental isopiestic molalities of the KCl(aq) reference solutions mR, m1 of NaH2PO4(aq) solutions, m2 of KH2PO4(aq) solutions, and molality-based osmotic coefficients ϕ of NaH2PO4(aq) and KH2PO4(aq) at T = (298.15 ± 0.01) K, along with the combined standard uncertainties as calculated by the propagation of errors method (m° = 1 mol·kg−1)
Full size table
Table 11 Experimental isopiestic molalities of the KCl(aq) reference solutions mR, m1 of NaH2PO4 and m2 of KH2PO4 in the mixtures, and molality-based osmotic coefficients ϕ, for {yNaH2PO4 + (1 − y)KH2PO4}(aq) at T = (298.15 ± 0.01) K where y = 0.19108, along with the combined standard uncertainties as calculated by the propagation of errors method (m° = 1 mol·kg−1)
Full size table
Table 12 Experimental isopiestic molalities of the KCl(aq) reference solutions mR, m1 of NaH2PO4 and m2 of KH2PO4 in the mixtures, and molality-based osmotic coefficients ϕ, for {yNaH2PO4 + (1 − y)KH2PO4}(aq) at T = (298.15 ± 0.01) K where y = 0.38306, along with the combined standard uncertainties as calculated by the propagation of errors method (m° = 1 mol·kg−1)
Full size table
Table 13 Experimental isopiestic molalities of the KCl(aq) reference solutions mR, m1 of NaH2PO4 and m2 of KH2PO4 in the mixtures, and molality-based osmotic coefficients ϕ, for {yNaH2PO4 + (1 − y)KH2PO4}(aq) at T = (298.15 ± 0.01) K where y = 0.58192, along with the combined standard uncertainties as calculated by the propagation of errors method (m° = 1 mol·kg−1)
Full size table

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Ivanović, T., Popović, D.Ž., Miladinović, J. et al. Isopiestic Determination of the Osmotic and Activity Coefficients of the {yNaH2PO4 + (1 − y)KH2PO4}(aq) System at T = 298.15 K. J Solution Chem 48, 296–328 (2019). https://doi.org/10.1007/s10953-018-0839-4

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